diff --git a/Triangle.AbstractMachine.Disassembler/src/main/java/Triangle/AbstractMachine/Disassembler.java b/Triangle.AbstractMachine.Disassembler/src/main/java/Triangle/AbstractMachine/Disassembler.java
index aa71b4c..0cf8ff6 100644
--- a/Triangle.AbstractMachine.Disassembler/src/main/java/Triangle/AbstractMachine/Disassembler.java
+++ b/Triangle.AbstractMachine.Disassembler/src/main/java/Triangle/AbstractMachine/Disassembler.java
@@ -50,62 +50,18 @@ public class Disassembler {
 	 * @param r            the number of the register.
 	 * @param rightbracket the character to print after the register.
 	 */
-	private static void writeR(char leftbracket, int r, char rightbracket) {
+	private static void writeR(char leftbracket, Register r, char rightbracket) {
 
 		System.out.print(leftbracket);
-		switch (r) {
-		case Machine.CBr:
-			System.out.print("CB");
-			break;
-		case Machine.CTr:
-			System.out.print("CT");
-			break;
-		case Machine.PBr:
-			System.out.print("PB");
-			break;
-		case Machine.PTr:
-			System.out.print("PT");
-			break;
-		case Machine.SBr:
-			System.out.print("SB");
-			break;
-		case Machine.STr:
-			System.out.print("ST");
-			break;
-		case Machine.HBr:
-			System.out.print("HB");
-			break;
-		case Machine.HTr:
-			System.out.print("HT");
-			break;
-		case Machine.LBr:
-			System.out.print("LB");
-			break;
-		case Machine.L1r:
-			System.out.print("L1");
-			break;
-		case Machine.L2r:
-			System.out.print("L2");
-			break;
-		case Machine.L3r:
-			System.out.print("L3");
-			break;
-		case Machine.L4r:
-			System.out.print("L4");
-			break;
-		case Machine.L5r:
-			System.out.print("L5");
-			break;
-		case Machine.L6r:
-			System.out.print("L6");
-			break;
-		case Machine.CPr:
-			System.out.print("CP");
-			break;
-		}
+		System.out.print(r.toString());
 		System.out.print(rightbracket);
 	}
 
+	private static void writeR(char leftBracket, int r, char rightBracket) {
+		var register = Register.values()[r];
+		writeR(leftBracket, register, rightBracket);
+	}
+
 	/**
 	 * Writes a void n-field of an instruction.
 	 */
@@ -142,89 +98,90 @@ public class Disassembler {
 	 * @param d the displacment of the primitive routine.
 	 */
 	private static void writePrimitive(int d) {
-		switch (d) {
-		case Machine.idDisplacement:
+		var primitive = Primitive.values()[d];
+		switch (primitive) {
+		case ID:
 			System.out.print("id      ");
 			break;
-		case Machine.notDisplacement:
+		case NOT:
 			System.out.print("not     ");
 			break;
-		case Machine.andDisplacement:
+		case AND:
 			System.out.print("and     ");
 			break;
-		case Machine.orDisplacement:
+		case OR:
 			System.out.print("or      ");
 			break;
-		case Machine.succDisplacement:
+		case SUCC:
 			System.out.print("succ    ");
 			break;
-		case Machine.predDisplacement:
+		case PRED:
 			System.out.print("pred    ");
 			break;
-		case Machine.negDisplacement:
+		case NEG:
 			System.out.print("neg     ");
 			break;
-		case Machine.addDisplacement:
+		case ADD:
 			System.out.print("add     ");
 			break;
-		case Machine.subDisplacement:
+		case SUB:
 			System.out.print("sub     ");
 			break;
-		case Machine.multDisplacement:
+		case MULT:
 			System.out.print("mult    ");
 			break;
-		case Machine.divDisplacement:
+		case DIV:
 			System.out.print("div     ");
 			break;
-		case Machine.modDisplacement:
+		case MOD:
 			System.out.print("mod     ");
 			break;
-		case Machine.ltDisplacement:
+		case LT:
 			System.out.print("lt      ");
 			break;
-		case Machine.leDisplacement:
+		case LE:
 			System.out.print("le      ");
 			break;
-		case Machine.geDisplacement:
+		case GE:
 			System.out.print("ge      ");
 			break;
-		case Machine.gtDisplacement:
+		case GT:
 			System.out.print("gt      ");
 			break;
-		case Machine.eqDisplacement:
+		case EQ:
 			System.out.print("eq      ");
 			break;
-		case Machine.neDisplacement:
+		case NE:
 			System.out.print("ne      ");
 			break;
-		case Machine.eolDisplacement:
+		case EOL:
 			System.out.print("eol     ");
 			break;
-		case Machine.eofDisplacement:
+		case EOF:
 			System.out.print("eof     ");
 			break;
-		case Machine.getDisplacement:
+		case GET:
 			System.out.print("get     ");
 			break;
-		case Machine.putDisplacement:
+		case PUT:
 			System.out.print("put     ");
 			break;
-		case Machine.geteolDisplacement:
+		case GETEOL:
 			System.out.print("geteol  ");
 			break;
-		case Machine.puteolDisplacement:
+		case PUTEOL:
 			System.out.print("puteol  ");
 			break;
-		case Machine.getintDisplacement:
+		case GETINT:
 			System.out.print("getint  ");
 			break;
-		case Machine.putintDisplacement:
+		case PUTINT:
 			System.out.print("putint  ");
 			break;
-		case Machine.newDisplacement:
+		case NEW:
 			System.out.print("new     ");
 			break;
-		case Machine.disposeDisplacement:
+		case DISPOSE:
 			System.out.print("dispose ");
 			break;
 		}
@@ -237,98 +194,98 @@ public class Disassembler {
 	 */
 	private static void writeInstruction(Instruction instr) {
 
-		switch (instr.op) {
-		case Machine.LOADop:
+		switch (instr.opCode) {
+		case LOAD:
 			System.out.print("LOAD  ");
-			writeN(instr.n);
-			writeD(instr.d);
-			writeR('[', instr.r, ']');
+			writeN(instr.length);
+			writeD(instr.operand);
+			writeR('[', instr.register, ']');
 			break;
 
-		case Machine.LOADAop:
+		case LOADA:
 			System.out.print("LOADA ");
 			blankN();
-			writeD(instr.d);
-			writeR('[', instr.r, ']');
+			writeD(instr.operand);
+			writeR('[', instr.register, ']');
 			break;
 
-		case Machine.LOADIop:
+		case LOADI:
 			System.out.print("LOADI ");
-			writeN(instr.n);
+			writeN(instr.length);
 			break;
 
-		case Machine.LOADLop:
+		case LOADL:
 			System.out.print("LOADL ");
 			blankN();
-			writeD(instr.d);
+			writeD(instr.operand);
 			break;
 
-		case Machine.STOREop:
+		case STORE:
 			System.out.print("STORE ");
-			writeN(instr.n);
-			writeD(instr.d);
-			writeR('[', instr.r, ']');
+			writeN(instr.length);
+			writeD(instr.operand);
+			writeR('[', instr.register, ']');
 			break;
 
-		case Machine.STOREIop:
+		case STOREI:
 			System.out.print("STOREI");
-			writeN(instr.n);
+			writeN(instr.length);
 			break;
 
-		case Machine.CALLop:
+		case CALL:
 			System.out.print("CALL  ");
-			if (instr.r == Machine.PBr) {
+			if (instr.register == Register.PB) {
 				blankN();
-				writePrimitive(instr.d);
+				writePrimitive(instr.operand);
 			} else {
-				writeR('(', instr.n, ')');
+				writeR('(', instr.length, ')');
 				System.out.print("  ");
-				writeD(instr.d);
-				writeR('[', instr.r, ']');
+				writeD(instr.operand);
+				writeR('[', instr.register, ']');
 			}
 			break;
 
-		case Machine.CALLIop:
+		case CALLI:
 			System.out.print("CALLI ");
 			break;
 
-		case Machine.RETURNop:
+		case RETURN:
 			System.out.print("RETURN");
-			writeN(instr.n);
-			writeD(instr.d);
+			writeN(instr.length);
+			writeD(instr.operand);
 			break;
 
-		case Machine.PUSHop:
+		case PUSH:
 			System.out.print("PUSH  ");
 			blankN();
-			writeD(instr.d);
+			writeD(instr.operand);
 			break;
 
-		case Machine.POPop:
+		case POP:
 			System.out.print("POP   ");
-			writeN(instr.n);
-			writeD(instr.d);
+			writeN(instr.length);
+			writeD(instr.operand);
 			break;
 
-		case Machine.JUMPop:
+		case JUMP:
 			System.out.print("JUMP  ");
 			blankN();
-			writeD(instr.d);
-			writeR('[', instr.r, ']');
+			writeD(instr.operand);
+			writeR('[', instr.register, ']');
 			break;
 
-		case Machine.JUMPIop:
+		case JUMPI:
 			System.out.print("JUMPI ");
 			break;
 
-		case Machine.JUMPIFop:
+		case JUMPIF:
 			System.out.print("JUMPIF");
-			writeN(instr.n);
-			writeD(instr.d);
-			writeR('[', instr.r, ']');
+			writeN(instr.length);
+			writeD(instr.operand);
+			writeR('[', instr.register, ']');
 			break;
 
-		case Machine.HALTop:
+		case HALT:
 			System.out.print("HALT  ");
 		}
 	}
diff --git a/Triangle.AbstractMachine.Interpreter/src/main/java/Triangle/AbstractMachine/Interpreter.java b/Triangle.AbstractMachine.Interpreter/src/main/java/Triangle/AbstractMachine/Interpreter.java
index 3c1b610..3ce9b08 100644
--- a/Triangle.AbstractMachine.Interpreter/src/main/java/Triangle/AbstractMachine/Interpreter.java
+++ b/Triangle.AbstractMachine.Interpreter/src/main/java/Triangle/AbstractMachine/Interpreter.java
@@ -40,41 +40,46 @@ public class Interpreter {
 	static long accumulator;
 
 	static int content(int r) {
+		var register = Register.values()[r];
+		return content(register);
+	}
+
+	static int content(Register r) {
 		// Returns the current content of register r,
 		// even if r is one of the pseudo-registers L1..L6.
 
 		switch (r) {
-		case Machine.CBr:
+		case CB:
 			return CB;
-		case Machine.CTr:
+		case CT:
 			return CT;
-		case Machine.PBr:
+		case PB:
 			return Machine.PB;
-		case Machine.PTr:
+		case PT:
 			return Machine.PT;
-		case Machine.SBr:
+		case SB:
 			return SB;
-		case Machine.STr:
+		case ST:
 			return ST;
-		case Machine.HBr:
+		case HB:
 			return HB;
-		case Machine.HTr:
+		case HT:
 			return HT;
-		case Machine.LBr:
+		case LB:
 			return LB;
-		case Machine.L1r:
+		case L1:
 			return data[LB];
-		case Machine.L2r:
+		case L2:
 			return data[data[LB]];
-		case Machine.L3r:
+		case L3:
 			return data[data[data[LB]]];
-		case Machine.L4r:
+		case L4:
 			return data[data[data[data[LB]]]];
-		case Machine.L5r:
+		case L5:
 			return data[data[data[data[data[LB]]]]];
-		case Machine.L6r:
+		case L6:
 			return data[data[data[data[data[data[LB]]]]]];
-		case Machine.CPr:
+		case CP:
 			return CP;
 		default:
 			return 0;
@@ -85,7 +90,6 @@ public class Interpreter {
 
 	static void dump() {
 		// Writes a summary of the machine state.
-		int addr, staticLink, dynamicLink, localRegNum;
 
 		System.out.println("");
 		System.out.println("State of data store and registers:");
@@ -95,7 +99,7 @@ public class Interpreter {
 		else {
 			System.out.println("       HB-->");
 			System.out.println("            |--------|");
-			for (addr = HB - 1; addr >= HT; addr--) {
+			for (var addr = HB - 1; addr >= HT; addr--) {
 				System.out.print(addr + ":");
 				if (addr == HT)
 					System.out.print(" HT-->");
@@ -110,41 +114,43 @@ public class Interpreter {
 		if (ST == SB)
 			System.out.println("            |--------|          (stack is empty)");
 		else {
-			dynamicLink = LB;
-			staticLink = LB;
-			localRegNum = Machine.LBr;
+			var dynamicLink = LB;
+			var staticLink = LB;
+			var localRegNum = Register.LB;
 			System.out.println("      ST--> |////////|");
 			System.out.println("            |--------|");
-			for (addr = ST - 1; addr >= SB; addr--) {
+			for (var addr = ST - 1; addr >= SB; addr--) {
 				System.out.print(addr + ":");
 				if (addr == SB)
 					System.out.print(" SB-->");
 				else if (addr == staticLink) {
 					switch (localRegNum) {
-					case Machine.LBr:
+					case LB:
 						System.out.print(" LB-->");
 						break;
-					case Machine.L1r:
+					case L1:
 						System.out.print(" L1-->");
 						break;
-					case Machine.L2r:
+					case L2:
 						System.out.print(" L2-->");
 						break;
-					case Machine.L3r:
+					case L3:
 						System.out.print(" L3-->");
 						break;
-					case Machine.L4r:
+					case L4:
 						System.out.print(" L4-->");
 						break;
-					case Machine.L5r:
+					case L5:
 						System.out.print(" L5-->");
 						break;
-					case Machine.L6r:
+					case L6:
 						System.out.print(" L6-->");
 						break;
+					default:
+						break;
 					}
 					staticLink = data[addr];
-					localRegNum = localRegNum + 1;
+					localRegNum = Register.values()[localRegNum.ordinal() + 1];
 				} else
 					System.out.print("      ");
 				if ((addr == dynamicLink) && (dynamicLink != SB))
@@ -277,45 +283,46 @@ public class Interpreter {
 		int addr, size;
 		char ch;
 
-		switch (primitiveDisplacement) {
-		case Machine.idDisplacement:
+		var primitive = Primitive.values()[primitiveDisplacement];
+		switch (primitive) {
+		case ID:
 			break; // nothing to be done
-		case Machine.notDisplacement:
+		case NOT:
 			data[ST - 1] = toInt(!isTrue(data[ST - 1]));
 			break;
-		case Machine.andDisplacement:
+		case AND:
 			ST = ST - 1;
 			data[ST - 1] = toInt(isTrue(data[ST - 1]) & isTrue(data[ST]));
 			break;
-		case Machine.orDisplacement:
+		case OR:
 			ST = ST - 1;
 			data[ST - 1] = toInt(isTrue(data[ST - 1]) | isTrue(data[ST]));
 			break;
-		case Machine.succDisplacement:
+		case SUCC:
 			data[ST - 1] = overflowChecked(data[ST - 1] + 1);
 			break;
-		case Machine.predDisplacement:
+		case PRED:
 			data[ST - 1] = overflowChecked(data[ST - 1] - 1);
 			break;
-		case Machine.negDisplacement:
+		case NEG:
 			data[ST - 1] = -data[ST - 1];
 			break;
-		case Machine.addDisplacement:
+		case ADD:
 			ST = ST - 1;
 			accumulator = data[ST - 1];
 			data[ST - 1] = overflowChecked(accumulator + data[ST]);
 			break;
-		case Machine.subDisplacement:
+		case SUB:
 			ST = ST - 1;
 			accumulator = data[ST - 1];
 			data[ST - 1] = overflowChecked(accumulator - data[ST]);
 			break;
-		case Machine.multDisplacement:
+		case MULT:
 			ST = ST - 1;
 			accumulator = data[ST - 1];
 			data[ST - 1] = overflowChecked(accumulator * data[ST]);
 			break;
-		case Machine.divDisplacement:
+		case DIV:
 			ST = ST - 1;
 			accumulator = data[ST - 1];
 			if (data[ST] != 0)
@@ -323,7 +330,7 @@ public class Interpreter {
 			else
 				status = failedZeroDivide;
 			break;
-		case Machine.modDisplacement:
+		case MOD:
 			ST = ST - 1;
 			accumulator = data[ST - 1];
 			if (data[ST] != 0)
@@ -331,41 +338,41 @@ public class Interpreter {
 			else
 				status = failedZeroDivide;
 			break;
-		case Machine.ltDisplacement:
+		case LT:
 			ST = ST - 1;
 			data[ST - 1] = toInt(data[ST - 1] < data[ST]);
 			break;
-		case Machine.leDisplacement:
+		case LE:
 			ST = ST - 1;
 			data[ST - 1] = toInt(data[ST - 1] <= data[ST]);
 			break;
-		case Machine.geDisplacement:
+		case GE:
 			ST = ST - 1;
 			data[ST - 1] = toInt(data[ST - 1] >= data[ST]);
 			break;
-		case Machine.gtDisplacement:
+		case GT:
 			ST = ST - 1;
 			data[ST - 1] = toInt(data[ST - 1] > data[ST]);
 			break;
-		case Machine.eqDisplacement:
+		case EQ:
 			size = data[ST - 1]; // size of each comparand
 			ST = ST - 2 * size;
 			data[ST - 1] = toInt(equal(size, ST - 1, ST - 1 + size));
 			break;
-		case Machine.neDisplacement:
+		case NE:
 			size = data[ST - 1]; // size of each comparand
 			ST = ST - 2 * size;
 			data[ST - 1] = toInt(!equal(size, ST - 1, ST - 1 + size));
 			break;
-		case Machine.eolDisplacement:
+		case EOL:
 			data[ST] = toInt(currentChar == '\n');
 			ST = ST + 1;
 			break;
-		case Machine.eofDisplacement:
+		case EOF:
 			data[ST] = toInt(currentChar == -1);
 			ST = ST + 1;
 			break;
-		case Machine.getDisplacement:
+		case GET:
 			ST = ST - 1;
 			addr = data[ST];
 			try {
@@ -375,12 +382,12 @@ public class Interpreter {
 			}
 			data[addr] = currentChar;
 			break;
-		case Machine.putDisplacement:
+		case PUT:
 			ST = ST - 1;
 			ch = (char) data[ST];
 			System.out.print(ch);
 			break;
-		case Machine.geteolDisplacement:
+		case GETEOL:
 			try {
 				while ((currentChar = System.in.read()) != '\n')
 					;
@@ -388,10 +395,10 @@ public class Interpreter {
 				status = failedIOError;
 			}
 			break;
-		case Machine.puteolDisplacement:
+		case PUTEOL:
 			System.out.println("");
 			break;
-		case Machine.getintDisplacement:
+		case GETINT:
 			ST = ST - 1;
 			addr = data[ST];
 			try {
@@ -401,18 +408,18 @@ public class Interpreter {
 			}
 			data[addr] = (int) accumulator;
 			break;
-		case Machine.putintDisplacement:
+		case PUTINT:
 			ST = ST - 1;
 			accumulator = data[ST];
 			System.out.print(accumulator);
 			break;
-		case Machine.newDisplacement:
+		case NEW:
 			size = data[ST - 1];
 			checkSpace(size);
 			HT = HT - size;
 			data[ST - 1] = HT;
 			break;
-		case Machine.disposeDisplacement:
+		case DISPOSE:
 			ST = ST - 1; // no action taken at present
 			break;
 		}
@@ -422,7 +429,6 @@ public class Interpreter {
 		// Runs the program in code store.
 
 		Instruction currentInstr;
-		int op, r, n, d, addr, index;
 
 		// Initialize registers ...
 		ST = SB;
@@ -434,65 +440,67 @@ public class Interpreter {
 			// Fetch instruction ...
 			currentInstr = Machine.code[CP];
 			// Decode instruction ...
-			op = currentInstr.op;
-			r = currentInstr.r;
-			n = currentInstr.n;
-			d = currentInstr.d;
+			var op = currentInstr.opCode;
+			var r = currentInstr.register;
+			var n = currentInstr.length;
+			var d = currentInstr.operand;
+			int addr;
+
 			// Execute instruction ...
 			switch (op) {
-			case Machine.LOADop:
+			case LOAD:
 				addr = d + content(r);
 				checkSpace(n);
-				for (index = 0; index < n; index++)
+				for (var index = 0; index < n; index++)
 					data[ST + index] = data[addr + index];
 				ST = ST + n;
 				CP = CP + 1;
 				break;
-			case Machine.LOADAop:
+			case LOADA:
 				addr = d + content(r);
 				checkSpace(1);
 				data[ST] = addr;
 				ST = ST + 1;
 				CP = CP + 1;
 				break;
-			case Machine.LOADIop:
+			case LOADI:
 				ST = ST - 1;
 				addr = data[ST];
 				checkSpace(n);
-				for (index = 0; index < n; index++)
+				for (var index = 0; index < n; index++)
 					data[ST + index] = data[addr + index];
 				ST = ST + n;
 				CP = CP + 1;
 				break;
-			case Machine.LOADLop:
+			case LOADL:
 				checkSpace(1);
 				data[ST] = d;
 				ST = ST + 1;
 				CP = CP + 1;
 				break;
-			case Machine.STOREop:
+			case STORE:
 				addr = d + content(r);
 				ST = ST - n;
-				for (index = 0; index < n; index++)
+				for (var index = 0; index < n; index++)
 					data[addr + index] = data[ST + index];
 				CP = CP + 1;
 				break;
-			case Machine.STOREIop:
+			case STOREI:
 				ST = ST - 1;
 				addr = data[ST];
 				ST = ST - n;
-				for (index = 0; index < n; index++)
+				for (var index = 0; index < n; index++)
 					data[addr + index] = data[ST + index];
 				CP = CP + 1;
 				break;
-			case Machine.CALLop:
+			case CALL:
 				addr = d + content(r);
 				if (addr >= Machine.PB) {
 					callPrimitive(addr - Machine.PB);
 					CP = CP + 1;
 				} else {
 					checkSpace(3);
-					if ((0 <= n) && (n <= 15))
+					if (0 <= n && n <= 15)
 						data[ST] = content(n); // static link
 					else
 						status = failedInvalidInstruction;
@@ -503,7 +511,7 @@ public class Interpreter {
 					CP = addr;
 				}
 				break;
-			case Machine.CALLIop:
+			case CALLI:
 				ST = ST - 2;
 				addr = data[ST + 1];
 				if (addr >= Machine.PB) {
@@ -518,43 +526,43 @@ public class Interpreter {
 					CP = addr;
 				}
 				break;
-			case Machine.RETURNop:
+			case RETURN:
 				addr = LB - d;
 				CP = data[LB + 2];
 				LB = data[LB + 1];
 				ST = ST - n;
-				for (index = 0; index < n; index++)
+				for (var index = 0; index < n; index++)
 					data[addr + index] = data[ST + index];
 				ST = addr + n;
 				break;
-			case Machine.PUSHop:
+			case PUSH:
 				checkSpace(d);
 				ST = ST + d;
 				CP = CP + 1;
 				break;
-			case Machine.POPop:
+			case POP:
 				addr = ST - n - d;
 				ST = ST - n;
-				for (index = 0; index < n; index++)
+				for (var index = 0; index < n; index++)
 					data[addr + index] = data[ST + index];
 				ST = addr + n;
 				CP = CP + 1;
 				break;
-			case Machine.JUMPop:
+			case JUMP:
 				CP = d + content(r);
 				break;
-			case Machine.JUMPIop:
+			case JUMPI:
 				ST = ST - 1;
 				CP = data[ST];
 				break;
-			case Machine.JUMPIFop:
+			case JUMPIF:
 				ST = ST - 1;
 				if (data[ST] == n)
 					CP = d + content(r);
 				else
 					CP = CP + 1;
 				break;
-			case Machine.HALTop:
+			case HALT:
 				status = halted;
 				break;
 			}
diff --git a/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Instruction.java b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Instruction.java
index bdfb7e4..493c479 100644
--- a/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Instruction.java
+++ b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Instruction.java
@@ -21,13 +21,6 @@ import java.io.IOException;
 
 public class Instruction {
 
-	public Instruction() {
-		op = 0;
-		r = 0;
-		n = 0;
-		d = 0;
-	}
-
 	// Java has no type synonyms, so the following representations are
 	// assumed:
 	//
@@ -37,26 +30,36 @@ public class Instruction {
 	// Operand = -32767..+32767; {16 bits signed}
 
 	// Represents TAM instructions.
-	public int op; // OpCode
-	public int r; // RegisterNumber
-	public int n; // Length
-	public int d; // Operand
+	final OpCode opCode;
+	final Register register;
+	final int length;
+	int operand; // Not final to allow for patching jump address
 
+	public Instruction(OpCode opcode, Register register, int length, int operand) {
+		this.opCode = opcode;
+		this.register = register;
+		this.length = length;
+		this.operand = operand;
+	}
+
+	public void setOperand(int operand) {
+		this.operand = operand;
+	}
+	
 	public void write(DataOutputStream output) throws IOException {
-		output.writeInt(op);
-		output.writeInt(r);
-		output.writeInt(n);
-		output.writeInt(d);
+		output.writeInt(opCode.ordinal());
+		output.writeInt(register.ordinal());
+		output.writeInt(length);
+		output.writeInt(operand);
 	}
 
 	public static Instruction read(DataInputStream input) throws IOException {
-		Instruction inst = new Instruction();
 		try {
-			inst.op = input.readInt();
-			inst.r = input.readInt();
-			inst.n = input.readInt();
-			inst.d = input.readInt();
-			return inst;
+			var opCode = OpCode.values()[input.readInt()];
+			var register = Register.values()[input.readInt()];
+			var length = input.readInt();
+			var operand = input.readInt();
+			return new Instruction(opCode, register, length, operand);
 		} catch (EOFException s) {
 			return null;
 		}
diff --git a/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Machine.java b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Machine.java
index ef61e9e..2550d06 100644
--- a/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Machine.java
+++ b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Machine.java
@@ -31,10 +31,6 @@ public final class Machine {
 
 	// INSTRUCTIONS
 
-	// Operation codes
-	public final static int LOADop = 0, LOADAop = 1, LOADIop = 2, LOADLop = 3, STOREop = 4, STOREIop = 5, CALLop = 6,
-			CALLIop = 7, RETURNop = 8, PUSHop = 10, POPop = 11, JUMPop = 12, JUMPIop = 13, JUMPIFop = 14, HALTop = 15;
-
 	// CODE STORE
 
 	public static Instruction[] code = new Instruction[1024];
@@ -46,9 +42,6 @@ public final class Machine {
 
 	// REGISTER NUMBERS
 
-	public final static int CBr = 0, CTr = 1, PBr = 2, PTr = 3, SBr = 4, STr = 5, HBr = 6, HTr = 7, LBr = 8,
-			L1r = LBr + 1, L2r = LBr + 2, L3r = LBr + 3, L4r = LBr + 4, L5r = LBr + 5, L6r = LBr + 6, CPr = 15;
-
 	// DATA REPRESENTATION
 
 	public final static int booleanSize = 1, characterSize = 1, integerSize = 1, addressSize = 1,
@@ -58,14 +51,4 @@ public final class Machine {
 
 			falseRep = 0, trueRep = 1, maxintRep = 32767;
 
-	// ADDRESSES OF PRIMITIVE ROUTINES
-
-	public final static int idDisplacement = 1, notDisplacement = 2, andDisplacement = 3, orDisplacement = 4,
-			succDisplacement = 5, predDisplacement = 6, negDisplacement = 7, addDisplacement = 8, subDisplacement = 9,
-			multDisplacement = 10, divDisplacement = 11, modDisplacement = 12, ltDisplacement = 13, leDisplacement = 14,
-			geDisplacement = 15, gtDisplacement = 16, eqDisplacement = 17, neDisplacement = 18, eolDisplacement = 19,
-			eofDisplacement = 20, getDisplacement = 21, putDisplacement = 22, geteolDisplacement = 23,
-			puteolDisplacement = 24, getintDisplacement = 25, putintDisplacement = 26, newDisplacement = 27,
-			disposeDisplacement = 28;
-
 }
diff --git a/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/OpCode.java b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/OpCode.java
new file mode 100644
index 0000000..9781279
--- /dev/null
+++ b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/OpCode.java
@@ -0,0 +1,5 @@
+package Triangle.AbstractMachine;
+
+public enum OpCode {
+	LOAD, LOADA, LOADI, LOADL, STORE, STOREI, CALL, CALLI, RETURN, PUSH, POP, JUMP, JUMPI, JUMPIF, HALT
+}
diff --git a/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Primitive.java b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Primitive.java
new file mode 100644
index 0000000..1ab3aa2
--- /dev/null
+++ b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Primitive.java
@@ -0,0 +1,6 @@
+package Triangle.AbstractMachine;
+
+public enum Primitive {
+	ID, NOT, AND, OR, SUCC, PRED, NEG, ADD, SUB, MULT, DIV, MOD, LT, LE, GE, GT, EQ, NE, EOL, EOF, GET, PUT, GETEOL,
+	PUTEOL, GETINT, PUTINT, NEW, DISPOSE
+}
diff --git a/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Register.java b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Register.java
new file mode 100644
index 0000000..1c91515
--- /dev/null
+++ b/Triangle.AbstractMachine/src/main/java/Triangle/AbstractMachine/Register.java
@@ -0,0 +1,5 @@
+package Triangle.AbstractMachine;
+
+public enum Register {
+	CB, CT, PB, PT, SB, ST, HB, HT, LB, L1, L2, L3, L4, L5, L6, CP
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AST.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AbstractSyntaxTree.java
similarity index 73%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AST.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AbstractSyntaxTree.java
index 7e52e5f..c5dd157 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AST.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AbstractSyntaxTree.java
@@ -14,12 +14,14 @@
 
 package Triangle.AbstractSyntaxTrees;
 
-import Triangle.CodeGenerator.RuntimeEntity;
+import Triangle.CodeGenerator.Entities.RuntimeEntity;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class AST {
+public abstract class AbstractSyntaxTree {
 
-	public AST(SourcePosition position) {
+	private final SourcePosition position;
+
+	public AbstractSyntaxTree(SourcePosition position) {
 		this.position = position;
 		entity = null;
 	}
@@ -28,13 +30,5 @@ public abstract class AST {
 		return position;
 	}
 
-	public abstract Object visit(Visitor v, Object o);
-
-	public final Object visit(Visitor v) {
-		return visit(v, null);
-	}
-	
-	public final SourcePosition position;
-	
 	public RuntimeEntity entity;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ActualParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ActualParameter.java
similarity index 58%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ActualParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ActualParameter.java
index 7924aac..0dc659b 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ActualParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ActualParameter.java
@@ -12,13 +12,21 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Actuals;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class ActualParameter extends AST {
+public abstract class ActualParameter extends AbstractSyntaxTree {
 
 	public ActualParameter(SourcePosition position) {
 		super(position);
 	}
+
+	public abstract <TArg, TResult> TResult visit(ActualParameterVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(ActualParameterVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ActualParameterSequence.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ActualParameterSequence.java
similarity index 58%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ActualParameterSequence.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ActualParameterSequence.java
index dc4509f..ff2c1a3 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ActualParameterSequence.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ActualParameterSequence.java
@@ -12,13 +12,21 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Actuals;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterSequenceVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class ActualParameterSequence extends AST {
+public abstract class ActualParameterSequence extends AbstractSyntaxTree {
 
 	public ActualParameterSequence(SourcePosition position) {
 		super(position);
 	}
+
+	public abstract <TArg, TResult> TResult visit(ActualParameterSequenceVisitor<TArg, TResult> v, TArg arg);
+
+	public <TResult> TResult visit(ActualParameterSequenceVisitor<Void, TResult> v) {
+		return visit(v, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ConstActualParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ConstActualParameter.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ConstActualParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ConstActualParameter.java
index a5a1fbe..7ff36d1 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ConstActualParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ConstActualParameter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Actuals;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class ConstActualParameter extends ActualParameter {
@@ -23,10 +25,9 @@ public class ConstActualParameter extends ActualParameter {
 		E = eAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitConstActualParameter(this, o);
+	public <TArg, TResult> TResult visit(ActualParameterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitConstActualParameter(this, arg);
 	}
 
-	public Expression E;
+	public final Expression E;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyActualParameterSequence.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/EmptyActualParameterSequence.java
similarity index 72%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyActualParameterSequence.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/EmptyActualParameterSequence.java
index dd6ef21..f5a5b41 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyActualParameterSequence.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/EmptyActualParameterSequence.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Actuals;
 
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterSequenceVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class EmptyActualParameterSequence extends ActualParameterSequence {
@@ -22,8 +23,7 @@ public class EmptyActualParameterSequence extends ActualParameterSequence {
 		super(position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitEmptyActualParameterSequence(this, o);
+	public <TArg, TResult> TResult visit(ActualParameterSequenceVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitEmptyActualParameterSequence(this, arg);
 	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FuncActualParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/FuncActualParameter.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FuncActualParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/FuncActualParameter.java
index 51378f3..d7dae8c 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FuncActualParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/FuncActualParameter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Actuals;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class FuncActualParameter extends ActualParameter {
@@ -23,10 +25,9 @@ public class FuncActualParameter extends ActualParameter {
 		I = iAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitFuncActualParameter(this, o);
+	public <TArg, TResult> TResult visit(ActualParameterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitFuncActualParameter(this, arg);
 	}
 
-	public Identifier I;
+	public final Identifier I;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleActualParameterSequence.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/MultipleActualParameterSequence.java
similarity index 70%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleActualParameterSequence.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/MultipleActualParameterSequence.java
index 9279fda..4144b05 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleActualParameterSequence.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/MultipleActualParameterSequence.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Actuals;
 
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterSequenceVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class MultipleActualParameterSequence extends ActualParameterSequence {
@@ -25,11 +26,10 @@ public class MultipleActualParameterSequence extends ActualParameterSequence {
 		APS = apsAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitMultipleActualParameterSequence(this, o);
+	public <TArg, TResult> TResult visit(ActualParameterSequenceVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitMultipleActualParameterSequence(this, arg);
 	}
 
-	public ActualParameter AP;
-	public ActualParameterSequence APS;
+	public final ActualParameter AP;
+	public final ActualParameterSequence APS;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ProcActualParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ProcActualParameter.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ProcActualParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ProcActualParameter.java
index c17c04c..3724cb4 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ProcActualParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/ProcActualParameter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Actuals;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class ProcActualParameter extends ActualParameter {
@@ -23,10 +25,9 @@ public class ProcActualParameter extends ActualParameter {
 		I = iAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitProcActualParameter(this, o);
+	public <TArg, TResult> TResult visit(ActualParameterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitProcActualParameter(this, arg);
 	}
 
-	public Identifier I;
+	public final Identifier I;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleActualParameterSequence.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/SingleActualParameterSequence.java
similarity index 71%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleActualParameterSequence.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/SingleActualParameterSequence.java
index 9ffbfb7..6a712ea 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleActualParameterSequence.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/SingleActualParameterSequence.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Actuals;
 
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterSequenceVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SingleActualParameterSequence extends ActualParameterSequence {
@@ -23,10 +24,9 @@ public class SingleActualParameterSequence extends ActualParameterSequence {
 		AP = apAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSingleActualParameterSequence(this, o);
+	public <TArg, TResult> TResult visit(ActualParameterSequenceVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSingleActualParameterSequence(this, arg);
 	}
 
-	public ActualParameter AP;
+	public final ActualParameter AP;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VarActualParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/VarActualParameter.java
similarity index 69%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VarActualParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/VarActualParameter.java
index a2e6f47..d6dc72f 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VarActualParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Actuals/VarActualParameter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Actuals;
 
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterVisitor;
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class VarActualParameter extends ActualParameter {
@@ -23,10 +25,9 @@ public class VarActualParameter extends ActualParameter {
 		V = vAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitVarActualParameter(this, o);
+	public <TArg, TResult> TResult visit(ActualParameterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitVarActualParameter(this, arg);
 	}
 
-	public Vname V;
+	public final Vname V;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ArrayAggregate.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/ArrayAggregate.java
similarity index 59%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ArrayAggregate.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/ArrayAggregate.java
index 2d0bc96..8cb0cc3 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ArrayAggregate.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/ArrayAggregate.java
@@ -12,11 +12,13 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Aggregates;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Visitors.ArrayAggregateVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class ArrayAggregate extends AST {
+public abstract class ArrayAggregate extends AbstractSyntaxTree {
 
 	public ArrayAggregate(SourcePosition position) {
 		super(position);
@@ -24,4 +26,10 @@ public abstract class ArrayAggregate extends AST {
 	}
 
 	public int elemCount;
+
+	public abstract <TArg, TResult> TResult visit(ArrayAggregateVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(ArrayAggregateVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleArrayAggregate.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/MultipleArrayAggregate.java
similarity index 67%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleArrayAggregate.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/MultipleArrayAggregate.java
index a699ebc..d5de6cc 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleArrayAggregate.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/MultipleArrayAggregate.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Aggregates;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Visitors.ArrayAggregateVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class MultipleArrayAggregate extends ArrayAggregate {
@@ -24,11 +26,10 @@ public class MultipleArrayAggregate extends ArrayAggregate {
 		AA = aaAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitMultipleArrayAggregate(this, o);
+	public <TArg, TResult> TResult visit(ArrayAggregateVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitMultipleArrayAggregate(this, arg);
 	}
 
-	public Expression E;
-	public ArrayAggregate AA;
+	public final Expression E;
+	public final ArrayAggregate AA;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleRecordAggregate.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/MultipleRecordAggregate.java
similarity index 59%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleRecordAggregate.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/MultipleRecordAggregate.java
index 95a1ad5..cbc572a 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleRecordAggregate.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/MultipleRecordAggregate.java
@@ -12,26 +12,27 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Aggregates;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.RecordAggregateVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class MultipleRecordAggregate extends RecordAggregate {
 
-	public MultipleRecordAggregate(Identifier iAST, Expression eAST, RecordAggregate raAST,
-			SourcePosition position) {
+	public MultipleRecordAggregate(Identifier iAST, Expression eAST, RecordAggregate raAST, SourcePosition position) {
 		super(position);
 		I = iAST;
 		E = eAST;
 		RA = raAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitMultipleRecordAggregate(this, o);
+	public <TArg, TResult> TResult visit(RecordAggregateVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitMultipleRecordAggregate(this, arg);
 	}
 
-	public Identifier I;
-	public Expression E;
-	public RecordAggregate RA;
+	public final Identifier I;
+	public final Expression E;
+	public final RecordAggregate RA;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/RecordAggregate.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/RecordAggregate.java
similarity index 56%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/RecordAggregate.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/RecordAggregate.java
index b149068..8350870 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/RecordAggregate.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/RecordAggregate.java
@@ -12,11 +12,14 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Aggregates;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Types.FieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.RecordAggregateVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class RecordAggregate extends AST {
+public abstract class RecordAggregate extends AbstractSyntaxTree {
 
 	public RecordAggregate(SourcePosition position) {
 		super(position);
@@ -24,4 +27,10 @@ public abstract class RecordAggregate extends AST {
 	}
 
 	public FieldTypeDenoter type;
+
+	public abstract <TArg, TResult> TResult visit(RecordAggregateVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(RecordAggregateVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleArrayAggregate.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/SingleArrayAggregate.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleArrayAggregate.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/SingleArrayAggregate.java
index 8bc2b6b..c96b28e 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleArrayAggregate.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/SingleArrayAggregate.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Aggregates;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Visitors.ArrayAggregateVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SingleArrayAggregate extends ArrayAggregate {
@@ -23,10 +25,9 @@ public class SingleArrayAggregate extends ArrayAggregate {
 		E = eAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSingleArrayAggregate(this, o);
+	public <TArg, TResult> TResult visit(ArrayAggregateVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSingleArrayAggregate(this, arg);
 	}
 
-	public Expression E;
+	public final Expression E;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleRecordAggregate.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/SingleRecordAggregate.java
similarity index 64%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleRecordAggregate.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/SingleRecordAggregate.java
index fb4155c..ec67464 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleRecordAggregate.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Aggregates/SingleRecordAggregate.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Aggregates;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.RecordAggregateVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SingleRecordAggregate extends RecordAggregate {
@@ -24,11 +27,10 @@ public class SingleRecordAggregate extends RecordAggregate {
 		E = eAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSingleRecordAggregate(this, o);
+	public <TArg, TResult> TResult visit(RecordAggregateVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSingleRecordAggregate(this, arg);
 	}
 
-	public Identifier I;
-	public Expression E;
+	public final Identifier I;
+	public final Expression E;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AssignCommand.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/AssignCommand.java
similarity index 65%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AssignCommand.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/AssignCommand.java
index 5e3849c..e062d67 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AssignCommand.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/AssignCommand.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Commands;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class AssignCommand extends Command {
@@ -24,11 +27,10 @@ public class AssignCommand extends Command {
 		E = eAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitAssignCommand(this, o);
+	public <TArg, TResult> TResult visit(CommandVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitAssignCommand(this, arg);
 	}
 
-	public Vname V;
-	public Expression E;
+	public final Vname V;
+	public final Expression E;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CallCommand.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/CallCommand.java
similarity index 64%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CallCommand.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/CallCommand.java
index da944ef..be536e6 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CallCommand.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/CallCommand.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Commands;
 
+import Triangle.AbstractSyntaxTrees.Actuals.ActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class CallCommand extends Command {
@@ -24,11 +27,10 @@ public class CallCommand extends Command {
 		APS = apsAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitCallCommand(this, o);
+	public <TArg, TResult> TResult visit(CommandVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitCallCommand(this, arg);
 	}
 
-	public Identifier I;
-	public ActualParameterSequence APS;
+	public final Identifier I;
+	public final ActualParameterSequence APS;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Command.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/Command.java
similarity index 59%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Command.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/Command.java
index 97f08d3..b171be0 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Command.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/Command.java
@@ -12,13 +12,21 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Commands;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class Command extends AST {
+public abstract class Command extends AbstractSyntaxTree {
 
 	public Command(SourcePosition position) {
 		super(position);
 	}
+
+	public abstract <TArg, TResult> TResult visit(CommandVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(CommandVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyCommand.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/EmptyCommand.java
similarity index 74%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyCommand.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/EmptyCommand.java
index 7d35d61..023ec28 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyCommand.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/EmptyCommand.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Commands;
 
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class EmptyCommand extends Command {
@@ -22,8 +23,7 @@ public class EmptyCommand extends Command {
 		super(position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitEmptyCommand(this, o);
+	public <TArg, TResult> TResult visit(CommandVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitEmptyCommand(this, arg);
 	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IfCommand.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/IfCommand.java
similarity index 69%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IfCommand.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/IfCommand.java
index 372a16c..a004763 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IfCommand.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/IfCommand.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Commands;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class IfCommand extends Command {
@@ -25,11 +27,10 @@ public class IfCommand extends Command {
 		C2 = c2AST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitIfCommand(this, o);
+	public <TArg, TResult> TResult visit(CommandVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitIfCommand(this, arg);
 	}
 
-	public Expression E;
-	public Command C1, C2;
+	public final Expression E;
+	public final Command C1, C2;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/LetCommand.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/LetCommand.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/LetCommand.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/LetCommand.java
index 85a38c6..7409304 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/LetCommand.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/LetCommand.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Commands;
 
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class LetCommand extends Command {
@@ -24,11 +26,10 @@ public class LetCommand extends Command {
 		C = cAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitLetCommand(this, o);
+	public <TArg, TResult> TResult visit(CommandVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitLetCommand(this, arg);
 	}
 
-	public Declaration D;
-	public Command C;
+	public final Declaration D;
+	public final Command C;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SequentialCommand.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/SequentialCommand.java
similarity index 74%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SequentialCommand.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/SequentialCommand.java
index 78bc131..9fda1fb 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SequentialCommand.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/SequentialCommand.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Commands;
 
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SequentialCommand extends Command {
@@ -24,10 +25,9 @@ public class SequentialCommand extends Command {
 		C2 = c2AST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSequentialCommand(this, o);
+	public <TArg, TResult> TResult visit(CommandVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSequentialCommand(this, arg);
 	}
 
-	public Command C1, C2;
+	public final Command C1, C2;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/WhileCommand.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/WhileCommand.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/WhileCommand.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/WhileCommand.java
index 57d4aa4..f3e38a7 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/WhileCommand.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Commands/WhileCommand.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Commands;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class WhileCommand extends Command {
@@ -24,11 +26,10 @@ public class WhileCommand extends Command {
 		C = cAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitWhileCommand(this, o);
+	public <TArg, TResult> TResult visit(CommandVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitWhileCommand(this, arg);
 	}
 
-	public Expression E;
-	public Command C;
+	public final Expression E;
+	public final Command C;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/BinaryOperatorDeclaration.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/BinaryOperatorDeclaration.java
similarity index 66%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/BinaryOperatorDeclaration.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/BinaryOperatorDeclaration.java
index 80edf9d..b22b2f8 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/BinaryOperatorDeclaration.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/BinaryOperatorDeclaration.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Declarations;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Operator;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class BinaryOperatorDeclaration extends Declaration {
@@ -27,11 +30,10 @@ public class BinaryOperatorDeclaration extends Declaration {
 		RES = resultAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitBinaryOperatorDeclaration(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitBinaryOperatorDeclaration(this, arg);
 	}
 
-	public Operator O;
-	public TypeDenoter ARG1, ARG2, RES;
+	public final Operator O;
+	public final TypeDenoter ARG1, ARG2, RES;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ConstDeclaration.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/ConstDeclaration.java
similarity index 64%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ConstDeclaration.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/ConstDeclaration.java
index 116b5e7..1d13f3c 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ConstDeclaration.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/ConstDeclaration.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Declarations;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class ConstDeclaration extends Declaration {
@@ -24,11 +27,10 @@ public class ConstDeclaration extends Declaration {
 		E = eAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitConstDeclaration(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitConstDeclaration(this, arg);
 	}
 
-	public Identifier I;
-	public Expression E;
+	public final Identifier I;
+	public final Expression E;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declaration.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/Declaration.java
similarity index 60%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declaration.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/Declaration.java
index 7a8e6c8..1d21bcf 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declaration.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/Declaration.java
@@ -12,11 +12,13 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Declarations;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class Declaration extends AST {
+public abstract class Declaration extends AbstractSyntaxTree {
 
 	public Declaration(SourcePosition position) {
 		super(position);
@@ -24,4 +26,10 @@ public abstract class Declaration extends AST {
 	}
 
 	public boolean duplicated;
+
+	public abstract <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FuncDeclaration.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/FuncDeclaration.java
similarity index 59%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FuncDeclaration.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/FuncDeclaration.java
index 32cfde0..240d558 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FuncDeclaration.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/FuncDeclaration.java
@@ -12,8 +12,13 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Declarations;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Formals.FormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class FuncDeclaration extends Declaration {
@@ -27,13 +32,12 @@ public class FuncDeclaration extends Declaration {
 		E = eAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitFuncDeclaration(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitFuncDeclaration(this, arg);
 	}
 
-	public Identifier I;
-	public FormalParameterSequence FPS;
+	public final Identifier I;
+	public final FormalParameterSequence FPS;
 	public TypeDenoter T;
-	public Expression E;
+	public final Expression E;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ProcDeclaration.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/ProcDeclaration.java
similarity index 60%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ProcDeclaration.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/ProcDeclaration.java
index 45eeb43..ab08f52 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ProcDeclaration.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/ProcDeclaration.java
@@ -12,8 +12,12 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Declarations;
 
+import Triangle.AbstractSyntaxTrees.Commands.Command;
+import Triangle.AbstractSyntaxTrees.Formals.FormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class ProcDeclaration extends Declaration {
@@ -25,12 +29,11 @@ public class ProcDeclaration extends Declaration {
 		C = cAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitProcDeclaration(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitProcDeclaration(this, arg);
 	}
 
-	public Identifier I;
-	public FormalParameterSequence FPS;
-	public Command C;
+	public final Identifier I;
+	public final FormalParameterSequence FPS;
+	public final Command C;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SequentialDeclaration.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/SequentialDeclaration.java
similarity index 73%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SequentialDeclaration.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/SequentialDeclaration.java
index 51014df..1003c9f 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SequentialDeclaration.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/SequentialDeclaration.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Declarations;
 
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SequentialDeclaration extends Declaration {
@@ -24,10 +25,9 @@ public class SequentialDeclaration extends Declaration {
 		D2 = d2AST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSequentialDeclaration(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSequentialDeclaration(this, arg);
 	}
 
-	public Declaration D1, D2;
+	public final Declaration D1, D2;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/UnaryOperatorDeclaration.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/UnaryOperatorDeclaration.java
similarity index 61%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/UnaryOperatorDeclaration.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/UnaryOperatorDeclaration.java
index 7237804..2bb619c 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/UnaryOperatorDeclaration.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/UnaryOperatorDeclaration.java
@@ -12,25 +12,26 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Declarations;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Operator;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class UnaryOperatorDeclaration extends Declaration {
 
-	public UnaryOperatorDeclaration(Operator oAST, TypeDenoter argAST, TypeDenoter resultAST,
-			SourcePosition position) {
+	public UnaryOperatorDeclaration(Operator oAST, TypeDenoter argAST, TypeDenoter resultAST, SourcePosition position) {
 		super(position);
 		O = oAST;
 		ARG = argAST;
 		RES = resultAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitUnaryOperatorDeclaration(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitUnaryOperatorDeclaration(this, arg);
 	}
 
-	public Operator O;
-	public TypeDenoter ARG, RES;
+	public final Operator O;
+	public final TypeDenoter ARG, RES;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VarDeclaration.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/VarDeclaration.java
similarity index 67%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VarDeclaration.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/VarDeclaration.java
index ed06634..ce8a50f 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VarDeclaration.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Declarations/VarDeclaration.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Declarations;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class VarDeclaration extends Declaration {
@@ -24,11 +27,10 @@ public class VarDeclaration extends Declaration {
 		T = tAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitVarDeclaration(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitVarDeclaration(this, arg);
 	}
 
-	public Identifier I;
+	public final Identifier I;
 	public TypeDenoter T;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ArrayExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/ArrayExpression.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ArrayExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/ArrayExpression.java
index 03baf73..8337b9d 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ArrayExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/ArrayExpression.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Aggregates.ArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class ArrayExpression extends Expression {
@@ -23,10 +25,9 @@ public class ArrayExpression extends Expression {
 		AA = aaAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitArrayExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitArrayExpression(this, arg);
 	}
 
-	public ArrayAggregate AA;
+	public final ArrayAggregate AA;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/BinaryExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/BinaryExpression.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/BinaryExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/BinaryExpression.java
index 9d154af..d5e2626 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/BinaryExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/BinaryExpression.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Operator;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class BinaryExpression extends Expression {
@@ -25,11 +27,10 @@ public class BinaryExpression extends Expression {
 		E2 = e2AST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitBinaryExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitBinaryExpression(this, arg);
 	}
 
-	public Expression E1, E2;
-	public Operator O;
+	public final Expression E1, E2;
+	public final Operator O;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CallExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/CallExpression.java
similarity index 63%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CallExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/CallExpression.java
index 4fdfa02..20580f8 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CallExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/CallExpression.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Actuals.ActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class CallExpression extends Expression {
@@ -24,11 +27,10 @@ public class CallExpression extends Expression {
 		APS = apsAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitCallExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitCallExpression(this, arg);
 	}
 
-	public Identifier I;
-	public ActualParameterSequence APS;
+	public final Identifier I;
+	public final ActualParameterSequence APS;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CharacterExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/CharacterExpression.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CharacterExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/CharacterExpression.java
index 3b5d688..47cb1e3 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CharacterExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/CharacterExpression.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Terminals.CharacterLiteral;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class CharacterExpression extends Expression {
@@ -23,10 +25,9 @@ public class CharacterExpression extends Expression {
 		CL = clAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitCharacterExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitCharacterExpression(this, arg);
 	}
 
-	public CharacterLiteral CL;
+	public final CharacterLiteral CL;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/EmptyExpression.java
similarity index 74%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/EmptyExpression.java
index 9e24680..58d173d 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/EmptyExpression.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class EmptyExpression extends Expression {
@@ -22,8 +23,7 @@ public class EmptyExpression extends Expression {
 		super(position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitEmptyExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitEmptyExpression(this, arg);
 	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/Expression.java
similarity index 57%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/Expression.java
index 569267a..0182ddf 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/Expression.java
@@ -12,11 +12,14 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class Expression extends AST {
+public abstract class Expression extends AbstractSyntaxTree {
 
 	public Expression(SourcePosition position) {
 		super(position);
@@ -24,4 +27,10 @@ public abstract class Expression extends AST {
 	}
 
 	public TypeDenoter type;
+
+	public abstract <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IfExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/IfExpression.java
similarity index 74%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IfExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/IfExpression.java
index 1142766..71f4209 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IfExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/IfExpression.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class IfExpression extends Expression {
@@ -25,10 +26,9 @@ public class IfExpression extends Expression {
 		E3 = e3AST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitIfExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitIfExpression(this, arg);
 	}
 
-	public Expression E1, E2, E3;
+	public final Expression E1, E2, E3;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IntegerExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/IntegerExpression.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IntegerExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/IntegerExpression.java
index a30879e..7284c3c 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IntegerExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/IntegerExpression.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Terminals.IntegerLiteral;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class IntegerExpression extends Expression {
@@ -23,10 +25,9 @@ public class IntegerExpression extends Expression {
 		IL = ilAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitIntegerExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitIntegerExpression(this, arg);
 	}
 
-	public IntegerLiteral IL;
+	public final IntegerLiteral IL;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/LetExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/LetExpression.java
similarity index 67%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/LetExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/LetExpression.java
index f96fb33..d08228e 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/LetExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/LetExpression.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class LetExpression extends Expression {
@@ -24,11 +26,10 @@ public class LetExpression extends Expression {
 		E = eAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitLetExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitLetExpression(this, arg);
 	}
 
-	public Declaration D;
-	public Expression E;
+	public final Declaration D;
+	public final Expression E;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/RecordExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/RecordExpression.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/RecordExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/RecordExpression.java
index 3f3dd23..bf6723b 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/RecordExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/RecordExpression.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Aggregates.RecordAggregate;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class RecordExpression extends Expression {
@@ -23,10 +25,9 @@ public class RecordExpression extends Expression {
 		RA = raAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitRecordExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitRecordExpression(this, arg);
 	}
 
-	public RecordAggregate RA;
+	public final RecordAggregate RA;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/UnaryExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/UnaryExpression.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/UnaryExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/UnaryExpression.java
index 1589235..14a931b 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/UnaryExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/UnaryExpression.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Operator;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class UnaryExpression extends Expression {
@@ -24,11 +26,10 @@ public class UnaryExpression extends Expression {
 		E = eAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitUnaryExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitUnaryExpression(this, arg);
 	}
 
-	public Expression E;
-	public Operator O;
+	public final Expression E;
+	public final Operator O;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VnameExpression.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/VnameExpression.java
similarity index 69%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VnameExpression.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/VnameExpression.java
index 100993d..f1a58da 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VnameExpression.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Expressions/VnameExpression.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Expressions;
 
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class VnameExpression extends Expression {
@@ -23,10 +25,9 @@ public class VnameExpression extends Expression {
 		V = vAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitVnameExpression(this, o);
+	public <TArg, TResult> TResult visit(ExpressionVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitVnameExpression(this, arg);
 	}
 
-	public Vname V;
+	public final Vname V;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ConstFormalParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/ConstFormalParameter.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ConstFormalParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/ConstFormalParameter.java
index b05ff0b..ff138ef 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ConstFormalParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/ConstFormalParameter.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Formals;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class ConstFormalParameter extends FormalParameter {
@@ -24,20 +27,20 @@ public class ConstFormalParameter extends FormalParameter {
 		T = tAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitConstFormalParameter(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitConstFormalParameter(this, arg);
 	}
 
-	public Identifier I;
-	public TypeDenoter T;
-
 	@Override
 	public boolean equals(Object fpAST) {
 		if (fpAST instanceof ConstFormalParameter) {
-			ConstFormalParameter cfpAST = (ConstFormalParameter) fpAST;
+			var cfpAST = (ConstFormalParameter) fpAST;
 			return T.equals(cfpAST.T);
-		} else
+		} else {
 			return false;
+		}
 	}
+
+	public final Identifier I;
+	public TypeDenoter T;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyFormalParameterSequence.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/EmptyFormalParameterSequence.java
similarity index 75%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyFormalParameterSequence.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/EmptyFormalParameterSequence.java
index d7aaace..84a10ec 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/EmptyFormalParameterSequence.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/EmptyFormalParameterSequence.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Formals;
 
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterSequenceVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class EmptyFormalParameterSequence extends FormalParameterSequence {
@@ -22,9 +23,8 @@ public class EmptyFormalParameterSequence extends FormalParameterSequence {
 		super(position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitEmptyFormalParameterSequence(this, o);
+	public <TArg, TResult> TResult visit(FormalParameterSequenceVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitEmptyFormalParameterSequence(this, arg);
 	}
 
 	@Override
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FormalParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/FormalParameter.java
similarity index 66%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FormalParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/FormalParameter.java
index 448a53c..6a9d0ec 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FormalParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/FormalParameter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Formals;
 
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public abstract class FormalParameter extends Declaration {
@@ -25,4 +27,9 @@ public abstract class FormalParameter extends Declaration {
 	@Override
 	public abstract boolean equals(Object fpAST);
 
+	public abstract <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FormalParameterSequence.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/FormalParameterSequence.java
similarity index 59%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FormalParameterSequence.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/FormalParameterSequence.java
index 8266327..d2997a8 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FormalParameterSequence.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/FormalParameterSequence.java
@@ -12,11 +12,13 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Formals;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterSequenceVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class FormalParameterSequence extends AST {
+public abstract class FormalParameterSequence extends AbstractSyntaxTree {
 
 	public FormalParameterSequence(SourcePosition position) {
 		super(position);
@@ -24,4 +26,10 @@ public abstract class FormalParameterSequence extends AST {
 
 	@Override
 	public abstract boolean equals(Object fpsAST);
+
+	public abstract <TArg, TResult> TResult visit(FormalParameterSequenceVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(FormalParameterSequenceVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FuncFormalParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/FuncFormalParameter.java
similarity index 71%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FuncFormalParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/FuncFormalParameter.java
index 7be3b1e..1f4b71b 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FuncFormalParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/FuncFormalParameter.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Formals;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class FuncFormalParameter extends FormalParameter {
@@ -26,9 +29,8 @@ public class FuncFormalParameter extends FormalParameter {
 		T = tAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitFuncFormalParameter(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitFuncFormalParameter(this, arg);
 	}
 
 	@Override
@@ -40,7 +42,7 @@ public class FuncFormalParameter extends FormalParameter {
 			return false;
 	}
 
-	public Identifier I;
-	public FormalParameterSequence FPS;
+	public final Identifier I;
+	public final FormalParameterSequence FPS;
 	public TypeDenoter T;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleFormalParameterSequence.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/MultipleFormalParameterSequence.java
similarity index 74%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleFormalParameterSequence.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/MultipleFormalParameterSequence.java
index 94d0a97..0905531 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleFormalParameterSequence.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/MultipleFormalParameterSequence.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Formals;
 
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterSequenceVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class MultipleFormalParameterSequence extends FormalParameterSequence {
@@ -25,9 +26,8 @@ public class MultipleFormalParameterSequence extends FormalParameterSequence {
 		FPS = fpsAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitMultipleFormalParameterSequence(this, o);
+	public <TArg, TResult> TResult visit(FormalParameterSequenceVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitMultipleFormalParameterSequence(this, arg);
 	}
 
 	@Override
@@ -35,10 +35,11 @@ public class MultipleFormalParameterSequence extends FormalParameterSequence {
 		if (fpsAST instanceof MultipleFormalParameterSequence) {
 			MultipleFormalParameterSequence mfpsAST = (MultipleFormalParameterSequence) fpsAST;
 			return FP.equals(mfpsAST.FP) && FPS.equals(mfpsAST.FPS);
-		} else
+		} else {
 			return false;
+		}
 	}
 
-	public FormalParameter FP;
-	public FormalParameterSequence FPS;
+	public final FormalParameter FP;
+	public final FormalParameterSequence FPS;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ProcFormalParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/ProcFormalParameter.java
similarity index 72%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ProcFormalParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/ProcFormalParameter.java
index 3e6931d..a866934 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ProcFormalParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/ProcFormalParameter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Formals;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class ProcFormalParameter extends FormalParameter {
@@ -24,20 +26,20 @@ public class ProcFormalParameter extends FormalParameter {
 		FPS = fpsAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitProcFormalParameter(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitProcFormalParameter(this, arg);
 	}
 
-	public Identifier I;
-	public FormalParameterSequence FPS;
-
 	@Override
 	public boolean equals(Object fpAST) {
 		if (fpAST instanceof ProcFormalParameter) {
 			ProcFormalParameter pfpAST = (ProcFormalParameter) fpAST;
 			return FPS.equals(pfpAST.FPS);
-		} else
+		} else {
 			return false;
+		}
 	}
+
+	public final Identifier I;
+	public final FormalParameterSequence FPS;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleFormalParameterSequence.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/SingleFormalParameterSequence.java
similarity index 75%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleFormalParameterSequence.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/SingleFormalParameterSequence.java
index d13f2b8..6110144 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleFormalParameterSequence.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/SingleFormalParameterSequence.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Formals;
 
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterSequenceVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SingleFormalParameterSequence extends FormalParameterSequence {
@@ -23,9 +24,8 @@ public class SingleFormalParameterSequence extends FormalParameterSequence {
 		FP = fpAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSingleFormalParameterSequence(this, o);
+	public <TArg, TResult> TResult visit(FormalParameterSequenceVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSingleFormalParameterSequence(this, arg);
 	}
 
 	@Override
@@ -33,9 +33,10 @@ public class SingleFormalParameterSequence extends FormalParameterSequence {
 		if (fpsAST instanceof SingleFormalParameterSequence) {
 			SingleFormalParameterSequence sfpsAST = (SingleFormalParameterSequence) fpsAST;
 			return FP.equals(sfpsAST.FP);
-		} else
+		} else {
 			return false;
+		}
 	}
 
-	public FormalParameter FP;
+	public final FormalParameter FP;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VarFormalParameter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/VarFormalParameter.java
similarity index 71%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VarFormalParameter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/VarFormalParameter.java
index fd97142..554475c 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/VarFormalParameter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Formals/VarFormalParameter.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Formals;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class VarFormalParameter extends FormalParameter {
@@ -24,20 +27,20 @@ public class VarFormalParameter extends FormalParameter {
 		T = tAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitVarFormalParameter(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitVarFormalParameter(this, arg);
 	}
 
-	public Identifier I;
-	public TypeDenoter T;
-
 	@Override
 	public boolean equals(Object fpAST) {
 		if (fpAST instanceof VarFormalParameter) {
 			VarFormalParameter vfpAST = (VarFormalParameter) fpAST;
 			return T.equals(vfpAST.T);
-		} else
+		} else {
 			return false;
+		}
 	}
+
+	public final Identifier I;
+	public TypeDenoter T;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Program.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Program.java
index bc9082b..52e0c10 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Program.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Program.java
@@ -14,19 +14,24 @@
 
 package Triangle.AbstractSyntaxTrees;
 
+import Triangle.AbstractSyntaxTrees.Commands.Command;
+import Triangle.AbstractSyntaxTrees.Visitors.ProgramVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public class Program extends AST {
+public class Program extends AbstractSyntaxTree {
 
 	public Program(Command cAST, SourcePosition position) {
 		super(position);
 		C = cAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitProgram(this, o);
+	public Command C;
+
+	public <TArg, TResult> TResult visit(ProgramVisitor<TArg, TResult> visitor, TArg arg) {
+		return visitor.visitProgram(this, arg);
 	}
 
-	public Command C;
+	public <TResult> TResult visit(ProgramVisitor<Void, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CharacterLiteral.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/CharacterLiteral.java
similarity index 64%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CharacterLiteral.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/CharacterLiteral.java
index 58c2ab0..5a171fb 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CharacterLiteral.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/CharacterLiteral.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Terminals;
 
+import Triangle.AbstractSyntaxTrees.Visitors.LiteralVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class CharacterLiteral extends Terminal {
@@ -22,9 +23,15 @@ public class CharacterLiteral extends Terminal {
 		super(spelling, position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitCharacterLiteral(this, o);
+	public <TArg, TResult> TResult visit(LiteralVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitCharacterLiteral(this, arg);
 	}
 
+	public <TArg, TResult> TResult visit(LiteralVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
+
+	public int getValue() {
+		return spelling.charAt(1);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Identifier.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/Identifier.java
similarity index 58%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Identifier.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/Identifier.java
index 6305dd0..b41ff32 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Identifier.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/Identifier.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Terminals;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.IdentifierVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class Identifier extends Terminal {
@@ -24,11 +27,14 @@ public class Identifier extends Terminal {
 		decl = null;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitIdentifier(this, o);
+	public TypeDenoter type;
+	public AbstractSyntaxTree decl; // Either a Declaration or a FieldTypeDenoter
+
+	public <TArg, TResult> TResult visit(IdentifierVisitor<TArg, TResult> visitor, TArg arg) {
+		return visitor.visitIdentifier(this, arg);
 	}
 
-	public TypeDenoter type;
-	public AST decl; // Either a Declaration or a FieldTypeDenoter
+	public <TArg, TResult> TResult visit(IdentifierVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IntegerLiteral.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/IntegerLiteral.java
similarity index 63%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IntegerLiteral.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/IntegerLiteral.java
index 50bf7ed..dfdd33d 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IntegerLiteral.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/IntegerLiteral.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Terminals;
 
+import Triangle.AbstractSyntaxTrees.Visitors.LiteralVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class IntegerLiteral extends Terminal {
@@ -22,9 +23,15 @@ public class IntegerLiteral extends Terminal {
 		super(spelling, position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitIntegerLiteral(this, o);
+	public <TArg, TResult> TResult visit(LiteralVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitIntegerLiteral(this, arg);
 	}
 
+	public <TArg, TResult> TResult visit(LiteralVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
+
+	public int getValue() {
+		return Integer.parseInt(spelling);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Operator.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/Operator.java
similarity index 64%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Operator.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/Operator.java
index a94a859..0cd50be 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Operator.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/Operator.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Terminals;
 
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
+import Triangle.AbstractSyntaxTrees.Visitors.OperatorVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class Operator extends Terminal {
@@ -23,10 +25,13 @@ public class Operator extends Terminal {
 		decl = null;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitOperator(this, o);
+	public Declaration decl;
+
+	public <TArg, TResult> TResult visit(OperatorVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitOperator(this, arg);
 	}
 
-	public Declaration decl;
+	public <TArg, TResult> TResult visit(OperatorVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminal.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/Terminal.java
similarity index 81%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminal.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/Terminal.java
index c4e6af4..c4747ff 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminal.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Terminals/Terminal.java
@@ -12,11 +12,12 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Terminals;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-abstract public class Terminal extends AST {
+public abstract class Terminal extends AbstractSyntaxTree {
 
 	public Terminal(String spelling, SourcePosition position) {
 		super(position);
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AnyTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/AnyTypeDenoter.java
similarity index 76%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AnyTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/AnyTypeDenoter.java
index 96aa351..cd5a7fc 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/AnyTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/AnyTypeDenoter.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class AnyTypeDenoter extends TypeDenoter {
@@ -22,9 +23,8 @@ public class AnyTypeDenoter extends TypeDenoter {
 		super(position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitAnyTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitAnyTypeDenoter(this, arg);
 	}
 
 	@Override
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ArrayTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/ArrayTypeDenoter.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ArrayTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/ArrayTypeDenoter.java
index 19ca206..26c74a7 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ArrayTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/ArrayTypeDenoter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Terminals.IntegerLiteral;
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class ArrayTypeDenoter extends TypeDenoter {
@@ -24,22 +26,22 @@ public class ArrayTypeDenoter extends TypeDenoter {
 		T = tAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitArrayTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitArrayTypeDenoter(this, arg);
 	}
 
 	@Override
 	public boolean equals(Object obj) {
-		if (obj != null && obj instanceof ErrorTypeDenoter)
+		if (obj != null && obj instanceof ErrorTypeDenoter) {
 			return true;
-		else if (obj != null && obj instanceof ArrayTypeDenoter)
+		} else if (obj != null && obj instanceof ArrayTypeDenoter) {
 			return this.IL.spelling.compareTo(((ArrayTypeDenoter) obj).IL.spelling) == 0
 					&& this.T.equals(((ArrayTypeDenoter) obj).T);
-		else
+		} else {
 			return false;
+		}
 	}
 
-	public IntegerLiteral IL;
+	public final IntegerLiteral IL;
 	public TypeDenoter T;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/BoolTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/BoolTypeDenoter.java
similarity index 72%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/BoolTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/BoolTypeDenoter.java
index 7941083..78828ab 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/BoolTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/BoolTypeDenoter.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class BoolTypeDenoter extends TypeDenoter {
@@ -22,16 +23,16 @@ public class BoolTypeDenoter extends TypeDenoter {
 		super(position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitBoolTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitBoolTypeDenoter(this, arg);
 	}
 
 	@Override
 	public boolean equals(Object obj) {
-		if ((obj != null) && (obj instanceof ErrorTypeDenoter))
+		if ((obj != null) && (obj instanceof ErrorTypeDenoter)) {
 			return true;
-		else
+		} else {
 			return ((obj != null) && (obj instanceof BoolTypeDenoter));
+		}
 	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CharTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/CharTypeDenoter.java
similarity index 72%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CharTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/CharTypeDenoter.java
index 01121ce..c6f53fd 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/CharTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/CharTypeDenoter.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class CharTypeDenoter extends TypeDenoter {
@@ -22,16 +23,16 @@ public class CharTypeDenoter extends TypeDenoter {
 		super(position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitCharTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitCharTypeDenoter(this, arg);
 	}
 
 	@Override
 	public boolean equals(Object obj) {
-		if (obj != null && obj instanceof ErrorTypeDenoter)
+		if (obj != null && obj instanceof ErrorTypeDenoter) {
 			return true;
-		else
+		} else {
 			return (obj != null && obj instanceof CharTypeDenoter);
+		}
 	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ErrorTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/ErrorTypeDenoter.java
similarity index 76%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ErrorTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/ErrorTypeDenoter.java
index f74cce5..551cdff 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/ErrorTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/ErrorTypeDenoter.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class ErrorTypeDenoter extends TypeDenoter {
@@ -22,9 +23,8 @@ public class ErrorTypeDenoter extends TypeDenoter {
 		super(position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitErrorTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitErrorTypeDenoter(this, arg);
 	}
 
 	@Override
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FieldTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/FieldTypeDenoter.java
similarity index 88%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FieldTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/FieldTypeDenoter.java
index eadb011..d729d1a 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/FieldTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/FieldTypeDenoter.java
@@ -12,7 +12,7 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
@@ -21,7 +21,4 @@ public abstract class FieldTypeDenoter extends TypeDenoter {
 	public FieldTypeDenoter(SourcePosition position) {
 		super(position);
 	}
-
-	@Override
-	public abstract boolean equals(Object obj);
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IntTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/IntTypeDenoter.java
similarity index 72%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IntTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/IntTypeDenoter.java
index 9356b3b..13834e6 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/IntTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/IntTypeDenoter.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class IntTypeDenoter extends TypeDenoter {
@@ -22,16 +23,16 @@ public class IntTypeDenoter extends TypeDenoter {
 		super(position);
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitIntTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitIntTypeDenoter(this, arg);
 	}
 
 	@Override
 	public boolean equals(Object obj) {
-		if (obj != null && obj instanceof ErrorTypeDenoter)
+		if (obj != null && obj instanceof ErrorTypeDenoter) {
 			return true;
-		else
+		} else {
 			return (obj != null && obj instanceof IntTypeDenoter);
+		}
 	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleFieldTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/MultipleFieldTypeDenoter.java
similarity index 77%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleFieldTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/MultipleFieldTypeDenoter.java
index 869a984..d414026 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/MultipleFieldTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/MultipleFieldTypeDenoter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class MultipleFieldTypeDenoter extends FieldTypeDenoter {
@@ -26,9 +28,8 @@ public class MultipleFieldTypeDenoter extends FieldTypeDenoter {
 		FT = ftAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitMultipleFieldTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitMultipleFieldTypeDenoter(this, arg);
 	}
 
 	@Override
@@ -36,11 +37,12 @@ public class MultipleFieldTypeDenoter extends FieldTypeDenoter {
 		if (obj != null && obj instanceof MultipleFieldTypeDenoter) {
 			MultipleFieldTypeDenoter ft = (MultipleFieldTypeDenoter) obj;
 			return (this.I.spelling.compareTo(ft.I.spelling) == 0) && this.T.equals(ft.T) && this.FT.equals(ft.FT);
-		} else
+		} else {
 			return false;
+		}
 	}
 
-	public Identifier I;
+	public final Identifier I;
 	public TypeDenoter T;
 	public FieldTypeDenoter FT;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/RecordTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/RecordTypeDenoter.java
similarity index 70%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/RecordTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/RecordTypeDenoter.java
index 1089fc0..0535c90 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/RecordTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/RecordTypeDenoter.java
@@ -12,8 +12,9 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class RecordTypeDenoter extends TypeDenoter {
@@ -23,19 +24,19 @@ public class RecordTypeDenoter extends TypeDenoter {
 		FT = ftAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitRecordTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitRecordTypeDenoter(this, arg);
 	}
 
 	@Override
 	public boolean equals(Object obj) {
-		if (obj != null && obj instanceof ErrorTypeDenoter)
+		if (obj != null && obj instanceof ErrorTypeDenoter) {
 			return true;
-		else if (obj != null && obj instanceof RecordTypeDenoter)
+		} else if (obj != null && obj instanceof RecordTypeDenoter) {
 			return this.FT.equals(((RecordTypeDenoter) obj).FT);
-		else
+		} else {
 			return false;
+		}
 	}
 
 	public FieldTypeDenoter FT;
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SimpleTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/SimpleTypeDenoter.java
similarity index 71%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SimpleTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/SimpleTypeDenoter.java
index 25ef45b..8d35166 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SimpleTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/SimpleTypeDenoter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SimpleTypeDenoter extends TypeDenoter {
@@ -23,9 +25,8 @@ public class SimpleTypeDenoter extends TypeDenoter {
 		I = iAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSimpleTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSimpleTypeDenoter(this, arg);
 	}
 
 	@Override
@@ -33,5 +34,5 @@ public class SimpleTypeDenoter extends TypeDenoter {
 		return false; // should not happen
 	}
 
-	public Identifier I;
+	public final Identifier I;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleFieldTypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/SingleFieldTypeDenoter.java
similarity index 75%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleFieldTypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/SingleFieldTypeDenoter.java
index 5a4056a..093f675 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SingleFieldTypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/SingleFieldTypeDenoter.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SingleFieldTypeDenoter extends FieldTypeDenoter {
@@ -24,9 +26,8 @@ public class SingleFieldTypeDenoter extends FieldTypeDenoter {
 		T = tAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSingleFieldTypeDenoter(this, o);
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSingleFieldTypeDenoter(this, arg);
 	}
 
 	@Override
@@ -34,10 +35,11 @@ public class SingleFieldTypeDenoter extends FieldTypeDenoter {
 		if (obj != null && obj instanceof SingleFieldTypeDenoter) {
 			SingleFieldTypeDenoter ft = (SingleFieldTypeDenoter) obj;
 			return (this.I.spelling.compareTo(ft.I.spelling) == 0) && this.T.equals(ft.T);
-		} else
+		} else {
 			return false;
+		}
 	}
 
-	public Identifier I;
+	public final Identifier I;
 	public TypeDenoter T;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/TypeDeclaration.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/TypeDeclaration.java
similarity index 67%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/TypeDeclaration.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/TypeDeclaration.java
index a5ff149..8870509 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/TypeDeclaration.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/TypeDeclaration.java
@@ -12,8 +12,11 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class TypeDeclaration extends Declaration {
@@ -24,11 +27,10 @@ public class TypeDeclaration extends Declaration {
 		T = tAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitTypeDeclaration(this, o);
+	public <TArg, TResult> TResult visit(DeclarationVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitTypeDeclaration(this, arg);
 	}
 
-	public Identifier I;
+	public final Identifier I;
 	public TypeDenoter T;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/TypeDenoter.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/TypeDenoter.java
similarity index 61%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/TypeDenoter.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/TypeDenoter.java
index 2d1e5de..015d08b 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/TypeDenoter.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Types/TypeDenoter.java
@@ -12,11 +12,13 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Types;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class TypeDenoter extends AST {
+public abstract class TypeDenoter extends AbstractSyntaxTree {
 
 	public TypeDenoter(SourcePosition position) {
 		super(position);
@@ -25,4 +27,9 @@ public abstract class TypeDenoter extends AST {
 	@Override
 	public abstract boolean equals(Object obj);
 
+	public abstract <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(TypeDenoterVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitor.java
deleted file mode 100644
index b40caac..0000000
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitor.java
+++ /dev/null
@@ -1,154 +0,0 @@
-/*
- * @(#)Visitor.java                        2.1 2003/10/07
- *
- * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
- * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
- * and School of Computer and Math Sciences, The Robert Gordon University,
- * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
- * All rights reserved.
- *
- * This software is provided free for educational use only. It may
- * not be used for commercial purposes without the prior written permission
- * of the authors.
- */
-
-package Triangle.AbstractSyntaxTrees;
-
-public interface Visitor {
-
-	// Commands
-	Object visitAssignCommand(AssignCommand ast, Object o);
-
-	Object visitCallCommand(CallCommand ast, Object o);
-
-	Object visitEmptyCommand(EmptyCommand ast, Object o);
-
-	Object visitIfCommand(IfCommand ast, Object o);
-
-	Object visitLetCommand(LetCommand ast, Object o);
-
-	Object visitSequentialCommand(SequentialCommand ast, Object o);
-
-	Object visitWhileCommand(WhileCommand ast, Object o);
-
-	// Expressions
-	Object visitArrayExpression(ArrayExpression ast, Object o);
-
-	Object visitBinaryExpression(BinaryExpression ast, Object o);
-
-	Object visitCallExpression(CallExpression ast, Object o);
-
-	Object visitCharacterExpression(CharacterExpression ast, Object o);
-
-	Object visitEmptyExpression(EmptyExpression ast, Object o);
-
-	Object visitIfExpression(IfExpression ast, Object o);
-
-	Object visitIntegerExpression(IntegerExpression ast, Object o);
-
-	Object visitLetExpression(LetExpression ast, Object o);
-
-	Object visitRecordExpression(RecordExpression ast, Object o);
-
-	Object visitUnaryExpression(UnaryExpression ast, Object o);
-
-	Object visitVnameExpression(VnameExpression ast, Object o);
-
-	// Declarations
-	Object visitBinaryOperatorDeclaration(BinaryOperatorDeclaration ast, Object o);
-
-	Object visitConstDeclaration(ConstDeclaration ast, Object o);
-
-	Object visitFuncDeclaration(FuncDeclaration ast, Object o);
-
-	Object visitProcDeclaration(ProcDeclaration ast, Object o);
-
-	Object visitSequentialDeclaration(SequentialDeclaration ast, Object o);
-
-	Object visitTypeDeclaration(TypeDeclaration ast, Object o);
-
-	Object visitUnaryOperatorDeclaration(UnaryOperatorDeclaration ast, Object o);
-
-	Object visitVarDeclaration(VarDeclaration ast, Object o);
-
-	// Array Aggregates
-	Object visitMultipleArrayAggregate(MultipleArrayAggregate ast, Object o);
-
-	Object visitSingleArrayAggregate(SingleArrayAggregate ast, Object o);
-
-	// Record Aggregates
-	Object visitMultipleRecordAggregate(MultipleRecordAggregate ast, Object o);
-
-	Object visitSingleRecordAggregate(SingleRecordAggregate ast, Object o);
-
-	// Formal Parameters
-	Object visitConstFormalParameter(ConstFormalParameter ast, Object o);
-
-	Object visitFuncFormalParameter(FuncFormalParameter ast, Object o);
-
-	Object visitProcFormalParameter(ProcFormalParameter ast, Object o);
-
-	Object visitVarFormalParameter(VarFormalParameter ast, Object o);
-
-	Object visitEmptyFormalParameterSequence(EmptyFormalParameterSequence ast, Object o);
-
-	Object visitMultipleFormalParameterSequence(MultipleFormalParameterSequence ast, Object o);
-
-	Object visitSingleFormalParameterSequence(SingleFormalParameterSequence ast, Object o);
-
-	// Actual Parameters
-	Object visitConstActualParameter(ConstActualParameter ast, Object o);
-
-	Object visitFuncActualParameter(FuncActualParameter ast, Object o);
-
-	Object visitProcActualParameter(ProcActualParameter ast, Object o);
-
-	Object visitVarActualParameter(VarActualParameter ast, Object o);
-
-	Object visitEmptyActualParameterSequence(EmptyActualParameterSequence ast, Object o);
-
-	Object visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, Object o);
-
-	Object visitSingleActualParameterSequence(SingleActualParameterSequence ast, Object o);
-
-	// Type Denoters
-	Object visitAnyTypeDenoter(AnyTypeDenoter ast, Object o);
-
-	Object visitArrayTypeDenoter(ArrayTypeDenoter ast, Object o);
-
-	Object visitBoolTypeDenoter(BoolTypeDenoter ast, Object o);
-
-	Object visitCharTypeDenoter(CharTypeDenoter ast, Object o);
-
-	Object visitErrorTypeDenoter(ErrorTypeDenoter ast, Object o);
-
-	Object visitSimpleTypeDenoter(SimpleTypeDenoter ast, Object o);
-
-	Object visitIntTypeDenoter(IntTypeDenoter ast, Object o);
-
-	Object visitRecordTypeDenoter(RecordTypeDenoter ast, Object o);
-
-	Object visitMultipleFieldTypeDenoter(MultipleFieldTypeDenoter ast, Object o);
-
-	Object visitSingleFieldTypeDenoter(SingleFieldTypeDenoter ast, Object o);
-
-	// Literals, Identifiers and Operators
-	Object visitCharacterLiteral(CharacterLiteral ast, Object o);
-
-	Object visitIdentifier(Identifier ast, Object o);
-
-	Object visitIntegerLiteral(IntegerLiteral ast, Object o);
-
-	Object visitOperator(Operator ast, Object o);
-
-	// Value-or-variable names
-	Object visitDotVname(DotVname ast, Object o);
-
-	Object visitSimpleVname(SimpleVname ast, Object o);
-
-	Object visitSubscriptVname(SubscriptVname ast, Object o);
-
-	// Programs
-	Object visitProgram(Program ast, Object o);
-
-}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ActualParameterSequenceVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ActualParameterSequenceVisitor.java
new file mode 100644
index 0000000..533552a
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ActualParameterSequenceVisitor.java
@@ -0,0 +1,15 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Actuals.EmptyActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.MultipleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.SingleActualParameterSequence;
+
+public interface ActualParameterSequenceVisitor<TArg, TResult> {
+
+	TResult visitEmptyActualParameterSequence(EmptyActualParameterSequence ast, TArg arg);
+
+	TResult visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, TArg arg);
+
+	TResult visitSingleActualParameterSequence(SingleActualParameterSequence ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ActualParameterVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ActualParameterVisitor.java
new file mode 100644
index 0000000..b376cde
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ActualParameterVisitor.java
@@ -0,0 +1,18 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Actuals.ConstActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.FuncActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.ProcActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.VarActualParameter;
+
+public interface ActualParameterVisitor<TArg, TResult> {
+
+	TResult visitConstActualParameter(ConstActualParameter ast, TArg arg);
+
+	TResult visitFuncActualParameter(FuncActualParameter ast, TArg arg);
+
+	TResult visitProcActualParameter(ProcActualParameter ast, TArg arg);
+
+	TResult visitVarActualParameter(VarActualParameter ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ArrayAggregateVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ArrayAggregateVisitor.java
new file mode 100644
index 0000000..197d7da
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ArrayAggregateVisitor.java
@@ -0,0 +1,12 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleArrayAggregate;
+
+public interface ArrayAggregateVisitor<TArg, TResult> {
+
+	TResult visitMultipleArrayAggregate(MultipleArrayAggregate ast, TArg arg);
+
+	TResult visitSingleArrayAggregate(SingleArrayAggregate ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/CommandVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/CommandVisitor.java
new file mode 100644
index 0000000..7f9efea
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/CommandVisitor.java
@@ -0,0 +1,27 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Commands.AssignCommand;
+import Triangle.AbstractSyntaxTrees.Commands.CallCommand;
+import Triangle.AbstractSyntaxTrees.Commands.EmptyCommand;
+import Triangle.AbstractSyntaxTrees.Commands.IfCommand;
+import Triangle.AbstractSyntaxTrees.Commands.LetCommand;
+import Triangle.AbstractSyntaxTrees.Commands.SequentialCommand;
+import Triangle.AbstractSyntaxTrees.Commands.WhileCommand;
+
+public interface CommandVisitor<TArg, TResult> {
+
+	TResult visitAssignCommand(AssignCommand ast, TArg arg);
+
+	TResult visitCallCommand(CallCommand ast, TArg arg);
+
+	TResult visitEmptyCommand(EmptyCommand ast, TArg arg);
+
+	TResult visitIfCommand(IfCommand ast, TArg arg);
+
+	TResult visitLetCommand(LetCommand ast, TArg arg);
+
+	TResult visitSequentialCommand(SequentialCommand ast, TArg arg);
+
+	TResult visitWhileCommand(WhileCommand ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/DeclarationVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/DeclarationVisitor.java
new file mode 100644
index 0000000..2d31430
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/DeclarationVisitor.java
@@ -0,0 +1,30 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Declarations.BinaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ConstDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.FuncDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ProcDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.SequentialDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.UnaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.VarDeclaration;
+import Triangle.AbstractSyntaxTrees.Types.TypeDeclaration;
+
+public interface DeclarationVisitor<TArg, TResult> extends FormalParameterVisitor<TArg, TResult> {
+
+	TResult visitBinaryOperatorDeclaration(BinaryOperatorDeclaration ast, TArg arg);
+
+	TResult visitConstDeclaration(ConstDeclaration ast, TArg arg);
+
+	TResult visitFuncDeclaration(FuncDeclaration ast, TArg arg);
+
+	TResult visitProcDeclaration(ProcDeclaration ast, TArg arg);
+
+	TResult visitSequentialDeclaration(SequentialDeclaration ast, TArg arg);
+
+	TResult visitTypeDeclaration(TypeDeclaration ast, TArg arg);
+
+	TResult visitUnaryOperatorDeclaration(UnaryOperatorDeclaration ast, TArg arg);
+
+	TResult visitVarDeclaration(VarDeclaration ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ExpressionVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ExpressionVisitor.java
new file mode 100644
index 0000000..776d5e6
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ExpressionVisitor.java
@@ -0,0 +1,39 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Expressions.ArrayExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.BinaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CallExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CharacterExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.EmptyExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.IfExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.IntegerExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.LetExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.RecordExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.UnaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.VnameExpression;
+
+public interface ExpressionVisitor<TArg, TResult> {
+
+	TResult visitArrayExpression(ArrayExpression ast, TArg arg);
+
+	TResult visitBinaryExpression(BinaryExpression ast, TArg arg);
+
+	TResult visitCallExpression(CallExpression ast, TArg arg);
+
+	TResult visitCharacterExpression(CharacterExpression ast, TArg arg);
+
+	TResult visitEmptyExpression(EmptyExpression ast, TArg arg);
+
+	TResult visitIfExpression(IfExpression ast, TArg arg);
+
+	TResult visitIntegerExpression(IntegerExpression ast, TArg arg);
+
+	TResult visitLetExpression(LetExpression ast, TArg arg);
+
+	TResult visitRecordExpression(RecordExpression ast, TArg arg);
+
+	TResult visitUnaryExpression(UnaryExpression ast, TArg arg);
+
+	TResult visitVnameExpression(VnameExpression ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/FieldTypeDenoterVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/FieldTypeDenoterVisitor.java
new file mode 100644
index 0000000..518f65e
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/FieldTypeDenoterVisitor.java
@@ -0,0 +1,12 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Types.MultipleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SingleFieldTypeDenoter;
+
+public interface FieldTypeDenoterVisitor<TArg, TResult> {
+
+	TResult visitMultipleFieldTypeDenoter(MultipleFieldTypeDenoter ast, TArg arg);
+
+	TResult visitSingleFieldTypeDenoter(SingleFieldTypeDenoter ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/FormalParameterSequenceVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/FormalParameterSequenceVisitor.java
new file mode 100644
index 0000000..7a570ba
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/FormalParameterSequenceVisitor.java
@@ -0,0 +1,15 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Formals.EmptyFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.MultipleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.SingleFormalParameterSequence;
+
+public interface FormalParameterSequenceVisitor<TArg, TResult> {
+
+	TResult visitEmptyFormalParameterSequence(EmptyFormalParameterSequence ast, TArg arg);
+
+	TResult visitMultipleFormalParameterSequence(MultipleFormalParameterSequence ast, TArg arg);
+
+	TResult visitSingleFormalParameterSequence(SingleFormalParameterSequence ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/FormalParameterVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/FormalParameterVisitor.java
new file mode 100644
index 0000000..2a9edd1
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/FormalParameterVisitor.java
@@ -0,0 +1,18 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Formals.ConstFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.FuncFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.ProcFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.VarFormalParameter;
+
+public interface FormalParameterVisitor<TArg, TResult> {
+
+	TResult visitConstFormalParameter(ConstFormalParameter ast, TArg arg);
+
+	TResult visitFuncFormalParameter(FuncFormalParameter ast, TArg arg);
+
+	TResult visitProcFormalParameter(ProcFormalParameter ast, TArg arg);
+
+	TResult visitVarFormalParameter(VarFormalParameter ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/IdentifierVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/IdentifierVisitor.java
new file mode 100644
index 0000000..40a6141
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/IdentifierVisitor.java
@@ -0,0 +1,9 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+
+public interface IdentifierVisitor<TArg, TResult> {
+
+	TResult visitIdentifier(Identifier ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/LiteralVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/LiteralVisitor.java
new file mode 100644
index 0000000..f5021e7
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/LiteralVisitor.java
@@ -0,0 +1,12 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Terminals.CharacterLiteral;
+import Triangle.AbstractSyntaxTrees.Terminals.IntegerLiteral;
+
+public interface LiteralVisitor<TArg, TResult> {
+
+	TResult visitCharacterLiteral(CharacterLiteral ast, TArg arg);
+
+	TResult visitIntegerLiteral(IntegerLiteral ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/OperatorVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/OperatorVisitor.java
new file mode 100644
index 0000000..bfeed74
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/OperatorVisitor.java
@@ -0,0 +1,9 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Terminals.Operator;
+
+public interface OperatorVisitor<TArg, TResult> {
+
+	TResult visitOperator(Operator ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ProgramVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ProgramVisitor.java
new file mode 100644
index 0000000..9601e1b
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/ProgramVisitor.java
@@ -0,0 +1,9 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Program;
+
+public interface ProgramVisitor<TArg, TResult> {
+
+	TResult visitProgram(Program ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/RecordAggregateVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/RecordAggregateVisitor.java
new file mode 100644
index 0000000..4a818e7
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/RecordAggregateVisitor.java
@@ -0,0 +1,12 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleRecordAggregate;
+
+public interface RecordAggregateVisitor<TArg, TResult> {
+
+	TResult visitMultipleRecordAggregate(MultipleRecordAggregate ast, TArg arg);
+
+	TResult visitSingleRecordAggregate(SingleRecordAggregate ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/TypeDenoterVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/TypeDenoterVisitor.java
new file mode 100644
index 0000000..2208acb
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/TypeDenoterVisitor.java
@@ -0,0 +1,30 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Types.AnyTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.ArrayTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.BoolTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.CharTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.ErrorTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.IntTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.RecordTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SimpleTypeDenoter;
+
+public interface TypeDenoterVisitor<TArg, TResult> extends FieldTypeDenoterVisitor<TArg, TResult> {
+
+	TResult visitAnyTypeDenoter(AnyTypeDenoter ast, TArg arg);
+
+	TResult visitArrayTypeDenoter(ArrayTypeDenoter ast, TArg arg);
+
+	TResult visitBoolTypeDenoter(BoolTypeDenoter ast, TArg arg);
+
+	TResult visitCharTypeDenoter(CharTypeDenoter ast, TArg arg);
+
+	TResult visitErrorTypeDenoter(ErrorTypeDenoter ast, TArg arg);
+
+	TResult visitSimpleTypeDenoter(SimpleTypeDenoter ast, TArg arg);
+
+	TResult visitIntTypeDenoter(IntTypeDenoter ast, TArg arg);
+
+	TResult visitRecordTypeDenoter(RecordTypeDenoter ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/VnameVisitor.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/VnameVisitor.java
new file mode 100644
index 0000000..7c1968a
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Visitors/VnameVisitor.java
@@ -0,0 +1,15 @@
+package Triangle.AbstractSyntaxTrees.Visitors;
+
+import Triangle.AbstractSyntaxTrees.Vnames.DotVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SimpleVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SubscriptVname;
+
+public interface VnameVisitor<TArg, TResult> {
+
+	TResult visitDotVname(DotVname ast, TArg arg);
+
+	TResult visitSimpleVname(SimpleVname ast, TArg arg);
+
+	TResult visitSubscriptVname(SubscriptVname ast, TArg arg);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/DotVname.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/DotVname.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/DotVname.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/DotVname.java
index f07f45f..4f25dfc 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/DotVname.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/DotVname.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Vnames;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.VnameVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class DotVname extends Vname {
@@ -24,11 +26,10 @@ public class DotVname extends Vname {
 		I = iAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitDotVname(this, o);
+	public <TArg, TResult> TResult visit(VnameVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitDotVname(this, arg);
 	}
 
-	public Identifier I;
-	public Vname V;
+	public final Identifier I;
+	public final Vname V;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SimpleVname.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/SimpleVname.java
similarity index 69%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SimpleVname.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/SimpleVname.java
index 4a89017..c107131 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SimpleVname.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/SimpleVname.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Vnames;
 
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Visitors.VnameVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SimpleVname extends Vname {
@@ -23,10 +25,9 @@ public class SimpleVname extends Vname {
 		I = iAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSimpleVname(this, o);
+	public <TArg, TResult> TResult visit(VnameVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSimpleVname(this, arg);
 	}
 
-	public Identifier I;
+	public final Identifier I;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SubscriptVname.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/SubscriptVname.java
similarity index 68%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SubscriptVname.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/SubscriptVname.java
index 1fc80a7..adff222 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/SubscriptVname.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/SubscriptVname.java
@@ -12,8 +12,10 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Vnames;
 
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Visitors.VnameVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
 public class SubscriptVname extends Vname {
@@ -24,11 +26,10 @@ public class SubscriptVname extends Vname {
 		E = eAST;
 	}
 
-	@Override
-	public Object visit(Visitor v, Object o) {
-		return v.visitSubscriptVname(this, o);
+	public <TArg, TResult> TResult visit(VnameVisitor<TArg, TResult> v, TArg arg) {
+		return v.visitSubscriptVname(this, arg);
 	}
 
-	public Expression E;
-	public Vname V;
+	public final Expression E;
+	public final Vname V;
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vname.java b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/Vname.java
similarity index 60%
rename from Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vname.java
rename to Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/Vname.java
index 7103179..c630829 100644
--- a/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vname.java
+++ b/Triangle.Compiler/src/main/java/Triangle/AbstractSyntaxTrees/Vnames/Vname.java
@@ -12,11 +12,14 @@
  * of the authors.
  */
 
-package Triangle.AbstractSyntaxTrees;
+package Triangle.AbstractSyntaxTrees.Vnames;
 
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.VnameVisitor;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public abstract class Vname extends AST {
+public abstract class Vname extends AbstractSyntaxTree {
 
 	public Vname(SourcePosition position) {
 		super(position);
@@ -27,4 +30,10 @@ public abstract class Vname extends AST {
 	public boolean variable, indexed;
 	public int offset;
 	public TypeDenoter type;
+
+	public abstract <TArg, TResult> TResult visit(VnameVisitor<TArg, TResult> visitor, TArg arg);
+
+	public <TArg, TResult> TResult visit(VnameVisitor<TArg, TResult> visitor) {
+		return visit(visitor, null);
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Emitter.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Emitter.java
new file mode 100644
index 0000000..f8aa600
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Emitter.java
@@ -0,0 +1,120 @@
+package Triangle.CodeGenerator;
+
+import java.io.DataOutputStream;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+import Triangle.ErrorReporter;
+import Triangle.AbstractMachine.Instruction;
+import Triangle.AbstractMachine.Machine;
+import Triangle.AbstractMachine.OpCode;
+import Triangle.AbstractMachine.Primitive;
+import Triangle.AbstractMachine.Register;
+
+public class Emitter {
+
+	// OBJECT CODE
+
+	// Implementation notes:
+	// Object code is generated directly into the TAM Code Store, starting at
+	// CB.
+	// The address of the next instruction is held in nextInstrAddr.
+
+	ErrorReporter errorReporter;
+
+	int nextInstrAddr;
+
+	public Emitter(ErrorReporter errorReporter) {
+		this.errorReporter = errorReporter;
+		nextInstrAddr = Machine.CB;
+	}
+
+	public int getNextInstrAddr() {
+		return nextInstrAddr;
+	}
+
+	public int emit(OpCode op) {
+		return emit(op, 0, Register.CB, 0);
+	}
+
+	public int emit(OpCode op, int operand) {
+		return emit(op, 0, Register.CB, operand);
+	}
+
+	public int emit(OpCode op, int length, int operand) {
+		return emit(op, length, Register.CB, operand);
+	}
+
+	public int emit(OpCode op, Register staticRegister, Register register, int operand) {
+		return emit(op, staticRegister.ordinal(), register, operand);
+	}
+
+	public int emit(OpCode op, Register register, int operand) {
+		return emit(op, 0, register, operand);
+	}
+
+	public int emit(OpCode op, Register register) {
+		return emit(op, 0, register, 0);
+	}
+
+	public int emit(OpCode op, int length, Register register) {
+		return emit(op, length, register, 0);
+	}
+
+	public int emit(OpCode op, Register register, Primitive primitive) {
+		return emit(op, 0, register, primitive.ordinal());
+	}
+
+	/**
+	 * Appends an instruction, with the given fields, to the object code.
+	 *
+	 * @param op       the opcode
+	 * @param length   the length field
+	 * @param register the register field
+	 * @param operand  the operand field
+	 * @return the code address of the new instruction
+	 **/
+	public int emit(OpCode op, int length, Register register, int operand) {
+
+		if (length > 255) {
+			errorReporter.reportRestriction("length of operand can't exceed 255 words");
+			length = 255; // to allow code generation to continue
+		}
+
+		var nextInstr = new Instruction(op, register, length, operand);
+
+		var currentInstrAddr = nextInstrAddr;
+		if (nextInstrAddr == Machine.PB) {
+			errorReporter.reportRestriction("too many instructions for code segment");
+		} else {
+			Machine.code[nextInstrAddr++] = nextInstr;
+		}
+		return currentInstrAddr;
+
+	}
+
+	// Patches the d-field of the instruction at address addr with the next
+	// instruction address.
+	public void patch(int addr) {
+		Machine.code[addr].setOperand(nextInstrAddr);
+	}
+
+	/**
+	 * Saves the object program in the given object file.
+	 * 
+	 * @param objectFile the object file
+	 */
+	public void saveObjectProgram(String objectFileName) {
+		try (var objectFile = new FileOutputStream(objectFileName)) {
+			var objectStream = new DataOutputStream(objectFile);
+			for (var addr = Machine.CB; addr < nextInstrAddr; addr++) {
+				Machine.code[addr].write(objectStream);
+			}
+		} catch (FileNotFoundException fnfe) {
+			System.err.println("Error opening object file: " + fnfe);
+		} catch (IOException ioe) {
+			System.err.println("Error writing object file: " + ioe);
+		}
+	}
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Encoder.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Encoder.java
index 168d165..82b8f69 100644
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Encoder.java
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Encoder.java
@@ -14,770 +14,755 @@
 
 package Triangle.CodeGenerator;
 
-import java.io.DataOutputStream;
-import java.io.FileNotFoundException;
-import java.io.FileOutputStream;
-import java.io.IOException;
-
 import Triangle.ErrorReporter;
 import Triangle.StdEnvironment;
-import Triangle.AbstractMachine.Instruction;
 import Triangle.AbstractMachine.Machine;
-import Triangle.AbstractSyntaxTrees.AST;
-import Triangle.AbstractSyntaxTrees.AnyTypeDenoter;
-import Triangle.AbstractSyntaxTrees.ArrayExpression;
-import Triangle.AbstractSyntaxTrees.ArrayTypeDenoter;
-import Triangle.AbstractSyntaxTrees.AssignCommand;
-import Triangle.AbstractSyntaxTrees.BinaryExpression;
-import Triangle.AbstractSyntaxTrees.BinaryOperatorDeclaration;
-import Triangle.AbstractSyntaxTrees.BoolTypeDenoter;
-import Triangle.AbstractSyntaxTrees.CallCommand;
-import Triangle.AbstractSyntaxTrees.CallExpression;
-import Triangle.AbstractSyntaxTrees.CharTypeDenoter;
-import Triangle.AbstractSyntaxTrees.CharacterExpression;
-import Triangle.AbstractSyntaxTrees.CharacterLiteral;
-import Triangle.AbstractSyntaxTrees.ConstActualParameter;
-import Triangle.AbstractSyntaxTrees.ConstDeclaration;
-import Triangle.AbstractSyntaxTrees.ConstFormalParameter;
-import Triangle.AbstractSyntaxTrees.Declaration;
-import Triangle.AbstractSyntaxTrees.DotVname;
-import Triangle.AbstractSyntaxTrees.EmptyActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.EmptyCommand;
-import Triangle.AbstractSyntaxTrees.EmptyExpression;
-import Triangle.AbstractSyntaxTrees.EmptyFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.ErrorTypeDenoter;
-import Triangle.AbstractSyntaxTrees.FuncActualParameter;
-import Triangle.AbstractSyntaxTrees.FuncDeclaration;
-import Triangle.AbstractSyntaxTrees.FuncFormalParameter;
-import Triangle.AbstractSyntaxTrees.Identifier;
-import Triangle.AbstractSyntaxTrees.IfCommand;
-import Triangle.AbstractSyntaxTrees.IfExpression;
-import Triangle.AbstractSyntaxTrees.IntTypeDenoter;
-import Triangle.AbstractSyntaxTrees.IntegerExpression;
-import Triangle.AbstractSyntaxTrees.IntegerLiteral;
-import Triangle.AbstractSyntaxTrees.LetCommand;
-import Triangle.AbstractSyntaxTrees.LetExpression;
-import Triangle.AbstractSyntaxTrees.MultipleActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.MultipleArrayAggregate;
-import Triangle.AbstractSyntaxTrees.MultipleFieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.MultipleFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.MultipleRecordAggregate;
-import Triangle.AbstractSyntaxTrees.Operator;
-import Triangle.AbstractSyntaxTrees.ProcActualParameter;
-import Triangle.AbstractSyntaxTrees.ProcDeclaration;
-import Triangle.AbstractSyntaxTrees.ProcFormalParameter;
+import Triangle.AbstractMachine.OpCode;
+import Triangle.AbstractMachine.Primitive;
+import Triangle.AbstractMachine.Register;
+import Triangle.AbstractSyntaxTrees.AbstractSyntaxTree;
 import Triangle.AbstractSyntaxTrees.Program;
-import Triangle.AbstractSyntaxTrees.RecordExpression;
-import Triangle.AbstractSyntaxTrees.RecordTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SequentialCommand;
-import Triangle.AbstractSyntaxTrees.SequentialDeclaration;
-import Triangle.AbstractSyntaxTrees.SimpleTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SimpleVname;
-import Triangle.AbstractSyntaxTrees.SingleActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.SingleArrayAggregate;
-import Triangle.AbstractSyntaxTrees.SingleFieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SingleFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.SingleRecordAggregate;
-import Triangle.AbstractSyntaxTrees.SubscriptVname;
-import Triangle.AbstractSyntaxTrees.TypeDeclaration;
-import Triangle.AbstractSyntaxTrees.UnaryExpression;
-import Triangle.AbstractSyntaxTrees.UnaryOperatorDeclaration;
-import Triangle.AbstractSyntaxTrees.VarActualParameter;
-import Triangle.AbstractSyntaxTrees.VarDeclaration;
-import Triangle.AbstractSyntaxTrees.VarFormalParameter;
-import Triangle.AbstractSyntaxTrees.Visitor;
-import Triangle.AbstractSyntaxTrees.Vname;
-import Triangle.AbstractSyntaxTrees.VnameExpression;
-import Triangle.AbstractSyntaxTrees.WhileCommand;
-
-public final class Encoder implements Visitor {
+import Triangle.AbstractSyntaxTrees.Actuals.ConstActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.EmptyActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.FuncActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.MultipleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.ProcActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.SingleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.VarActualParameter;
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Commands.AssignCommand;
+import Triangle.AbstractSyntaxTrees.Commands.CallCommand;
+import Triangle.AbstractSyntaxTrees.Commands.EmptyCommand;
+import Triangle.AbstractSyntaxTrees.Commands.IfCommand;
+import Triangle.AbstractSyntaxTrees.Commands.LetCommand;
+import Triangle.AbstractSyntaxTrees.Commands.SequentialCommand;
+import Triangle.AbstractSyntaxTrees.Commands.WhileCommand;
+import Triangle.AbstractSyntaxTrees.Declarations.BinaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ConstDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
+import Triangle.AbstractSyntaxTrees.Declarations.FuncDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ProcDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.SequentialDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.UnaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.VarDeclaration;
+import Triangle.AbstractSyntaxTrees.Expressions.ArrayExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.BinaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CallExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CharacterExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.EmptyExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.IfExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.IntegerExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.LetExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.RecordExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.UnaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.VnameExpression;
+import Triangle.AbstractSyntaxTrees.Formals.ConstFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.EmptyFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.FuncFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.MultipleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.ProcFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.SingleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.VarFormalParameter;
+import Triangle.AbstractSyntaxTrees.Terminals.CharacterLiteral;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Terminals.IntegerLiteral;
+import Triangle.AbstractSyntaxTrees.Terminals.Operator;
+import Triangle.AbstractSyntaxTrees.Types.AnyTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.ArrayTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.BoolTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.CharTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.ErrorTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.IntTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.MultipleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.RecordTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SimpleTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SingleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.TypeDeclaration;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterSequenceVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ArrayAggregateVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterSequenceVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.IdentifierVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.LiteralVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.OperatorVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ProgramVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.RecordAggregateVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.VnameVisitor;
+import Triangle.AbstractSyntaxTrees.Vnames.DotVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SimpleVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SubscriptVname;
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
+import Triangle.CodeGenerator.Entities.AddressableEntity;
+import Triangle.CodeGenerator.Entities.EqualityRoutine;
+import Triangle.CodeGenerator.Entities.FetchableEntity;
+import Triangle.CodeGenerator.Entities.Field;
+import Triangle.CodeGenerator.Entities.KnownAddress;
+import Triangle.CodeGenerator.Entities.KnownRoutine;
+import Triangle.CodeGenerator.Entities.KnownValue;
+import Triangle.CodeGenerator.Entities.PrimitiveRoutine;
+import Triangle.CodeGenerator.Entities.RuntimeEntity;
+import Triangle.CodeGenerator.Entities.TypeRepresentation;
+import Triangle.CodeGenerator.Entities.UnknownAddress;
+import Triangle.CodeGenerator.Entities.UnknownRoutine;
+import Triangle.CodeGenerator.Entities.UnknownValue;
+
+public final class Encoder
+		implements ActualParameterVisitor<Frame, Integer>, ActualParameterSequenceVisitor<Frame, Integer>,
+		ArrayAggregateVisitor<Frame, Integer>, CommandVisitor<Frame, Void>, DeclarationVisitor<Frame, Integer>,
+		ExpressionVisitor<Frame, Integer>, FormalParameterVisitor<Frame, Integer>,
+		FormalParameterSequenceVisitor<Frame, Integer>, IdentifierVisitor<Frame, Void>, LiteralVisitor<Void, Void>,
+		OperatorVisitor<Frame, Void>, ProgramVisitor<Frame, Void>, RecordAggregateVisitor<Frame, Integer>,
+		TypeDenoterVisitor<Frame, Integer>, VnameVisitor<Frame, RuntimeEntity> {
 
 	// Commands
 	@Override
-	public Object visitAssignCommand(AssignCommand ast, Object o) {
-		Frame frame = (Frame) o;
-		Integer valSize = (Integer) ast.E.visit(this, frame);
-		encodeStore(ast.V, new Frame(frame, valSize.intValue()), valSize.intValue());
+	public Void visitAssignCommand(AssignCommand ast, Frame frame) {
+		var valSize = ast.E.visit(this, frame);
+		encodeStore(ast.V, frame.expand(valSize), valSize);
 		return null;
 	}
 
 	@Override
-	public Object visitCallCommand(CallCommand ast, Object o) {
-		Frame frame = (Frame) o;
-		Integer argsSize = (Integer) ast.APS.visit(this, frame);
-		ast.I.visit(this, new Frame(frame.level, argsSize));
+	public Void visitCallCommand(CallCommand ast, Frame frame) {
+		var argsSize = ast.APS.visit(this, frame);
+		ast.I.visit(this, frame.replace(argsSize));
 		return null;
 	}
 
 	@Override
-	public Object visitEmptyCommand(EmptyCommand ast, Object o) {
+	public Void visitEmptyCommand(EmptyCommand ast, Frame frame) {
 		return null;
 	}
 
 	@Override
-	public Object visitIfCommand(IfCommand ast, Object o) {
-		Frame frame = (Frame) o;
-		int jumpifAddr, jumpAddr;
-
-		Integer valSize = (Integer) ast.E.visit(this, frame);
-		jumpifAddr = nextInstrAddr;
-		emit(Machine.JUMPIFop, Machine.falseRep, Machine.CBr, 0);
+	public Void visitIfCommand(IfCommand ast, Frame frame) {
+		ast.E.visit(this, frame);
+		var jumpifAddr = emitter.emit(OpCode.JUMPIF, Machine.falseRep, Register.CB, 0);
 		ast.C1.visit(this, frame);
-		jumpAddr = nextInstrAddr;
-		emit(Machine.JUMPop, 0, Machine.CBr, 0);
-		patch(jumpifAddr, nextInstrAddr);
+		var jumpAddr = emitter.emit(OpCode.JUMP, 0, Register.CB, 0);
+		emitter.patch(jumpifAddr);
 		ast.C2.visit(this, frame);
-		patch(jumpAddr, nextInstrAddr);
+		emitter.patch(jumpAddr);
 		return null;
 	}
 
 	@Override
-	public Object visitLetCommand(LetCommand ast, Object o) {
-		Frame frame = (Frame) o;
-		int extraSize = ((Integer) ast.D.visit(this, frame)).intValue();
-		ast.C.visit(this, new Frame(frame, extraSize));
-		if (extraSize > 0)
-			emit(Machine.POPop, 0, 0, extraSize);
+	public Void visitLetCommand(LetCommand ast, Frame frame) {
+		var extraSize = ast.D.visit(this, frame);
+		ast.C.visit(this, frame.expand(extraSize));
+		if (extraSize > 0) {
+			emitter.emit(OpCode.POP, extraSize);
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitSequentialCommand(SequentialCommand ast, Object o) {
-		ast.C1.visit(this, o);
-		ast.C2.visit(this, o);
+	public Void visitSequentialCommand(SequentialCommand ast, Frame frame) {
+		ast.C1.visit(this, frame);
+		ast.C2.visit(this, frame);
 		return null;
 	}
 
 	@Override
-	public Object visitWhileCommand(WhileCommand ast, Object o) {
-		Frame frame = (Frame) o;
-		int jumpAddr, loopAddr;
-
-		jumpAddr = nextInstrAddr;
-		emit(Machine.JUMPop, 0, Machine.CBr, 0);
-		loopAddr = nextInstrAddr;
+	public Void visitWhileCommand(WhileCommand ast, Frame frame) {
+		var jumpAddr = emitter.emit(OpCode.JUMP, 0, Register.CB, 0);
+		var loopAddr = emitter.getNextInstrAddr();
 		ast.C.visit(this, frame);
-		patch(jumpAddr, nextInstrAddr);
+		emitter.patch(jumpAddr);
 		ast.E.visit(this, frame);
-		emit(Machine.JUMPIFop, Machine.trueRep, Machine.CBr, loopAddr);
+		emitter.emit(OpCode.JUMPIF, Machine.trueRep, Register.CB, loopAddr);
 		return null;
 	}
 
 	// Expressions
 	@Override
-	public Object visitArrayExpression(ArrayExpression ast, Object o) {
-		ast.type.visit(this);
-		return ast.AA.visit(this, o);
+	public Integer visitArrayExpression(ArrayExpression ast, Frame frame) {
+		ast.type.visit(this, frame);
+		return ast.AA.visit(this, frame);
 	}
 
 	@Override
-	public Object visitBinaryExpression(BinaryExpression ast, Object o) {
-		Frame frame = (Frame) o;
-		Integer valSize = (Integer) ast.type.visit(this);
-		int valSize1 = ((Integer) ast.E1.visit(this, frame)).intValue();
-		Frame frame1 = new Frame(frame, valSize1);
-		int valSize2 = ((Integer) ast.E2.visit(this, frame1)).intValue();
-		Frame frame2 = new Frame(frame.level, valSize1 + valSize2);
+	public Integer visitBinaryExpression(BinaryExpression ast, Frame frame) {
+		var valSize = ast.type.visit(this);
+		var valSize1 = ast.E1.visit(this, frame);
+		var frame1 = frame.expand(valSize1);
+		var valSize2 = ast.E2.visit(this, frame1);
+		var frame2 = frame.replace(valSize1 + valSize2);
 		ast.O.visit(this, frame2);
 		return valSize;
 	}
 
 	@Override
-	public Object visitCallExpression(CallExpression ast, Object o) {
-		Frame frame = (Frame) o;
-		Integer valSize = (Integer) ast.type.visit(this);
-		Integer argsSize = (Integer) ast.APS.visit(this, frame);
-		ast.I.visit(this, new Frame(frame.level, argsSize));
+	public Integer visitCallExpression(CallExpression ast, Frame frame) {
+		var valSize = ast.type.visit(this);
+		var argsSize = ast.APS.visit(this, frame);
+		ast.I.visit(this, frame.replace(argsSize));
 		return valSize;
 	}
 
 	@Override
-	public Object visitCharacterExpression(CharacterExpression ast, Object o) {
-		Frame frame = (Frame) o;
-		Integer valSize = (Integer) ast.type.visit(this);
-		emit(Machine.LOADLop, 0, 0, ast.CL.spelling.charAt(1));
+	public Integer visitCharacterExpression(CharacterExpression ast, Frame frame) {
+		var valSize = ast.type.visit(this);
+		emitter.emit(OpCode.LOADL, ast.CL.spelling.charAt(1));
 		return valSize;
 	}
 
 	@Override
-	public Object visitEmptyExpression(EmptyExpression ast, Object o) {
-		return Integer.valueOf(0);
+	public Integer visitEmptyExpression(EmptyExpression ast, Frame frame) {
+		return 0;
 	}
 
 	@Override
-	public Object visitIfExpression(IfExpression ast, Object o) {
-		Frame frame = (Frame) o;
-		Integer valSize;
-		int jumpifAddr, jumpAddr;
-
+	public Integer visitIfExpression(IfExpression ast, Frame frame) {
 		ast.type.visit(this);
 		ast.E1.visit(this, frame);
-		jumpifAddr = nextInstrAddr;
-		emit(Machine.JUMPIFop, Machine.falseRep, Machine.CBr, 0);
-		valSize = (Integer) ast.E2.visit(this, frame);
-		jumpAddr = nextInstrAddr;
-		emit(Machine.JUMPop, 0, Machine.CBr, 0);
-		patch(jumpifAddr, nextInstrAddr);
-		valSize = (Integer) ast.E3.visit(this, frame);
-		patch(jumpAddr, nextInstrAddr);
+		var jumpifAddr = emitter.emit(OpCode.JUMPIF, Machine.falseRep, Register.CB, 0);
+		var valSize = ast.E2.visit(this, frame);
+		var jumpAddr = emitter.emit(OpCode.JUMP, 0, Register.CB, 0);
+		emitter.patch(jumpifAddr);
+		valSize = ast.E3.visit(this, frame);
+		emitter.patch(jumpAddr);
 		return valSize;
 	}
 
 	@Override
-	public Object visitIntegerExpression(IntegerExpression ast, Object o) {
-		Frame frame = (Frame) o;
-		Integer valSize = (Integer) ast.type.visit(this);
-		emit(Machine.LOADLop, 0, 0, Integer.parseInt(ast.IL.spelling));
+	public Integer visitIntegerExpression(IntegerExpression ast, Frame frame) {
+		var valSize = ast.type.visit(this);
+		emitter.emit(OpCode.LOADL, Integer.parseInt(ast.IL.spelling));
 		return valSize;
 	}
 
 	@Override
-	public Object visitLetExpression(LetExpression ast, Object o) {
-		Frame frame = (Frame) o;
+	public Integer visitLetExpression(LetExpression ast, Frame frame) {
 		ast.type.visit(this);
-		int extraSize = ((Integer) ast.D.visit(this, frame)).intValue();
-		Frame frame1 = new Frame(frame, extraSize);
-		Integer valSize = (Integer) ast.E.visit(this, frame1);
-		if (extraSize > 0)
-			emit(Machine.POPop, valSize.intValue(), 0, extraSize);
+		var extraSize = ast.D.visit(this, frame);
+		var frame1 = frame.expand(extraSize);
+		var valSize = ast.E.visit(this, frame1);
+		if (extraSize > 0) {
+			emitter.emit(OpCode.POP, valSize, extraSize);
+		}
 		return valSize;
 	}
 
 	@Override
-	public Object visitRecordExpression(RecordExpression ast, Object o) {
+	public Integer visitRecordExpression(RecordExpression ast, Frame frame) {
 		ast.type.visit(this);
-		return ast.RA.visit(this, o);
+		return ast.RA.visit(this, frame);
 	}
 
 	@Override
-	public Object visitUnaryExpression(UnaryExpression ast, Object o) {
-		Frame frame = (Frame) o;
-		Integer valSize = (Integer) ast.type.visit(this);
+	public Integer visitUnaryExpression(UnaryExpression ast, Frame frame) {
+		var valSize = ast.type.visit(this);
 		ast.E.visit(this, frame);
-		ast.O.visit(this, new Frame(frame.level, valSize.intValue()));
+		ast.O.visit(this, frame.replace(valSize));
 		return valSize;
 	}
 
 	@Override
-	public Object visitVnameExpression(VnameExpression ast, Object o) {
-		Frame frame = (Frame) o;
-		Integer valSize = (Integer) ast.type.visit(this);
-		encodeFetch(ast.V, frame, valSize.intValue());
+	public Integer visitVnameExpression(VnameExpression ast, Frame frame) {
+		var valSize = ast.type.visit(this);
+		encodeFetch(ast.V, frame, valSize);
 		return valSize;
 	}
 
 	// Declarations
 	@Override
-	public Object visitBinaryOperatorDeclaration(BinaryOperatorDeclaration ast, Object o) {
-		return Integer.valueOf(0);
+	public Integer visitBinaryOperatorDeclaration(BinaryOperatorDeclaration ast, Frame frame) {
+		return 0;
 	}
 
 	@Override
-	public Object visitConstDeclaration(ConstDeclaration ast, Object o) {
-		Frame frame = (Frame) o;
-		int extraSize = 0;
-
+	public Integer visitConstDeclaration(ConstDeclaration ast, Frame frame) {
+		var extraSize = 0;
 		if (ast.E instanceof CharacterExpression) {
-			CharacterLiteral CL = ((CharacterExpression) ast.E).CL;
-			ast.entity = new KnownValue(Machine.characterSize, characterValuation(CL.spelling));
+			var CL = ((CharacterExpression) ast.E).CL;
+			ast.entity = new KnownValue(Machine.characterSize, CL.getValue());
 		} else if (ast.E instanceof IntegerExpression) {
-			IntegerLiteral IL = ((IntegerExpression) ast.E).IL;
-			ast.entity = new KnownValue(Machine.integerSize, Integer.parseInt(IL.spelling));
+			var IL = ((IntegerExpression) ast.E).IL;
+			ast.entity = new KnownValue(Machine.integerSize, IL.getValue());
 		} else {
-			int valSize = ((Integer) ast.E.visit(this, frame)).intValue();
-			ast.entity = new UnknownValue(valSize, frame.level, frame.size);
+			var valSize = ast.E.visit(this, frame);
+			ast.entity = new UnknownValue(valSize, frame.getLevel(), frame.getSize());
 			extraSize = valSize;
 		}
 		writeTableDetails(ast);
-		return Integer.valueOf(extraSize);
+		return extraSize;
 	}
 
 	@Override
-	public Object visitFuncDeclaration(FuncDeclaration ast, Object o) {
-		Frame frame = (Frame) o;
-		int jumpAddr = nextInstrAddr;
-		int argsSize = 0, valSize = 0;
+	public Integer visitFuncDeclaration(FuncDeclaration ast, Frame frame) {
+		var argsSize = 0;
+		var valSize = 0;
 
-		emit(Machine.JUMPop, 0, Machine.CBr, 0);
-		ast.entity = new KnownRoutine(Machine.closureSize, frame.level, nextInstrAddr);
+		var jumpAddr = emitter.emit(OpCode.JUMP, 0, Register.CB, 0);
+		ast.entity = new KnownRoutine(Machine.closureSize, frame.getLevel(), emitter.getNextInstrAddr());
 		writeTableDetails(ast);
-		if (frame.level == Machine.maxRoutineLevel)
+		if (frame.getLevel() == Machine.maxRoutineLevel) {
 			reporter.reportRestriction("can't nest routines more than 7 deep");
-		else {
-			Frame frame1 = new Frame(frame.level + 1, 0);
-			argsSize = ((Integer) ast.FPS.visit(this, frame1)).intValue();
-			Frame frame2 = new Frame(frame.level + 1, Machine.linkDataSize);
-			valSize = ((Integer) ast.E.visit(this, frame2)).intValue();
+		} else {
+			var frame1 = frame.push(0);
+			argsSize = ast.FPS.visit(this, frame1);
+			var frame2 = frame.push(Machine.linkDataSize);
+			valSize = ast.E.visit(this, frame2);
 		}
-		emit(Machine.RETURNop, valSize, 0, argsSize);
-		patch(jumpAddr, nextInstrAddr);
-		return Integer.valueOf(0);
+		emitter.emit(OpCode.RETURN, valSize, argsSize);
+		emitter.patch(jumpAddr);
+		return 0;
 	}
 
 	@Override
-	public Object visitProcDeclaration(ProcDeclaration ast, Object o) {
-		Frame frame = (Frame) o;
-		int jumpAddr = nextInstrAddr;
-		int argsSize = 0;
-
-		emit(Machine.JUMPop, 0, Machine.CBr, 0);
-		ast.entity = new KnownRoutine(Machine.closureSize, frame.level, nextInstrAddr);
+	public Integer visitProcDeclaration(ProcDeclaration ast, Frame frame) {
+		var argsSize = 0;
+		var jumpAddr = emitter.emit(OpCode.JUMP, 0, Register.CB, 0);
+		ast.entity = new KnownRoutine(Machine.closureSize, frame.getLevel(), emitter.getNextInstrAddr());
 		writeTableDetails(ast);
-		if (frame.level == Machine.maxRoutineLevel)
+		if (frame.getLevel() == Machine.maxRoutineLevel) {
 			reporter.reportRestriction("can't nest routines so deeply");
-		else {
-			Frame frame1 = new Frame(frame.level + 1, 0);
-			argsSize = ((Integer) ast.FPS.visit(this, frame1)).intValue();
-			Frame frame2 = new Frame(frame.level + 1, Machine.linkDataSize);
+		} else {
+			var frame1 = frame.push(0);
+			argsSize = ast.FPS.visit(this, frame1);
+			var frame2 = frame.push(Machine.linkDataSize);
 			ast.C.visit(this, frame2);
 		}
-		emit(Machine.RETURNop, 0, 0, argsSize);
-		patch(jumpAddr, nextInstrAddr);
-		return Integer.valueOf(0);
+		emitter.emit(OpCode.RETURN, argsSize);
+		emitter.patch(jumpAddr);
+		return 0;
 	}
 
 	@Override
-	public Object visitSequentialDeclaration(SequentialDeclaration ast, Object o) {
-		Frame frame = (Frame) o;
-		int extraSize1, extraSize2;
-
-		extraSize1 = ((Integer) ast.D1.visit(this, frame)).intValue();
-		Frame frame1 = new Frame(frame, extraSize1);
-		extraSize2 = ((Integer) ast.D2.visit(this, frame1)).intValue();
-		return Integer.valueOf(extraSize1 + extraSize2);
+	public Integer visitSequentialDeclaration(SequentialDeclaration ast, Frame frame) {
+		var extraSize1 = ast.D1.visit(this, frame);
+		var frame1 = frame.expand(extraSize1);
+		var extraSize2 = ast.D2.visit(this, frame1);
+		return extraSize1 + extraSize2;
 	}
 
 	@Override
-	public Object visitTypeDeclaration(TypeDeclaration ast, Object o) {
+	public Integer visitTypeDeclaration(TypeDeclaration ast, Frame frame) {
 		// just to ensure the type's representation is decided
 		ast.T.visit(this);
-		return Integer.valueOf(0);
+		return 0;
 	}
 
 	@Override
-	public Object visitUnaryOperatorDeclaration(UnaryOperatorDeclaration ast, Object o) {
-		return Integer.valueOf(0);
+	public Integer visitUnaryOperatorDeclaration(UnaryOperatorDeclaration ast, Frame frame) {
+		return 0;
 	}
 
 	@Override
-	public Object visitVarDeclaration(VarDeclaration ast, Object o) {
-		Frame frame = (Frame) o;
-		int extraSize;
-
-		extraSize = ((Integer) ast.T.visit(this)).intValue();
-		emit(Machine.PUSHop, 0, 0, extraSize);
-		ast.entity = new KnownAddress(Machine.addressSize, frame.level, frame.size);
+	public Integer visitVarDeclaration(VarDeclaration ast, Frame frame) {
+		var extraSize = ast.T.visit(this);
+		emitter.emit(OpCode.PUSH, extraSize);
+		ast.entity = new KnownAddress(Machine.addressSize, frame.getLevel(), frame.getSize());
 		writeTableDetails(ast);
-		return Integer.valueOf(extraSize);
+		return extraSize;
 	}
 
 	// Array Aggregates
 	@Override
-	public Object visitMultipleArrayAggregate(MultipleArrayAggregate ast, Object o) {
-		Frame frame = (Frame) o;
-		int elemSize = ((Integer) ast.E.visit(this, frame)).intValue();
-		Frame frame1 = new Frame(frame, elemSize);
-		int arraySize = ((Integer) ast.AA.visit(this, frame1)).intValue();
-		return Integer.valueOf(elemSize + arraySize);
+	public Integer visitMultipleArrayAggregate(MultipleArrayAggregate ast, Frame frame) {
+		var elemSize = ast.E.visit(this, frame);
+		var frame1 = frame.expand(elemSize);
+		var arraySize = ast.AA.visit(this, frame1);
+		return elemSize + arraySize;
 	}
 
 	@Override
-	public Object visitSingleArrayAggregate(SingleArrayAggregate ast, Object o) {
-		return ast.E.visit(this, o);
+	public Integer visitSingleArrayAggregate(SingleArrayAggregate ast, Frame frame) {
+		return ast.E.visit(this, frame);
 	}
 
 	// Record Aggregates
 	@Override
-	public Object visitMultipleRecordAggregate(MultipleRecordAggregate ast, Object o) {
-		Frame frame = (Frame) o;
-		int fieldSize = ((Integer) ast.E.visit(this, frame)).intValue();
-		Frame frame1 = new Frame(frame, fieldSize);
-		int recordSize = ((Integer) ast.RA.visit(this, frame1)).intValue();
-		return Integer.valueOf(fieldSize + recordSize);
+	public Integer visitMultipleRecordAggregate(MultipleRecordAggregate ast, Frame frame) {
+		var fieldSize = ast.E.visit(this, frame);
+		var frame1 = frame.expand(fieldSize);
+		var recordSize = ast.RA.visit(this, frame1);
+		return fieldSize + recordSize;
 	}
 
 	@Override
-	public Object visitSingleRecordAggregate(SingleRecordAggregate ast, Object o) {
-		return ast.E.visit(this, o);
+	public Integer visitSingleRecordAggregate(SingleRecordAggregate ast, Frame frame) {
+		return ast.E.visit(this, frame);
 	}
 
 	// Formal Parameters
 	@Override
-	public Object visitConstFormalParameter(ConstFormalParameter ast, Object o) {
-		Frame frame = (Frame) o;
-		int valSize = ((Integer) ast.T.visit(this)).intValue();
-		ast.entity = new UnknownValue(valSize, frame.level, -frame.size - valSize);
+	public Integer visitConstFormalParameter(ConstFormalParameter ast, Frame frame) {
+		var valSize = ast.T.visit(this);
+		ast.entity = new UnknownValue(valSize, frame.getLevel(), -frame.getSize() - valSize);
 		writeTableDetails(ast);
-		return Integer.valueOf(valSize);
+		return valSize;
 	}
 
 	@Override
-	public Object visitFuncFormalParameter(FuncFormalParameter ast, Object o) {
-		Frame frame = (Frame) o;
-		int argsSize = Machine.closureSize;
-		ast.entity = new UnknownRoutine(Machine.closureSize, frame.level, -frame.size - argsSize);
+	public Integer visitFuncFormalParameter(FuncFormalParameter ast, Frame frame) {
+		var argsSize = Machine.closureSize;
+		ast.entity = new UnknownRoutine(Machine.closureSize, frame.getLevel(), -frame.getSize() - argsSize);
 		writeTableDetails(ast);
-		return Integer.valueOf(argsSize);
+		return argsSize;
 	}
 
 	@Override
-	public Object visitProcFormalParameter(ProcFormalParameter ast, Object o) {
-		Frame frame = (Frame) o;
-		int argsSize = Machine.closureSize;
-		ast.entity = new UnknownRoutine(Machine.closureSize, frame.level, -frame.size - argsSize);
+	public Integer visitProcFormalParameter(ProcFormalParameter ast, Frame frame) {
+		var argsSize = Machine.closureSize;
+		ast.entity = new UnknownRoutine(Machine.closureSize, frame.getLevel(), -frame.getSize() - argsSize);
 		writeTableDetails(ast);
-		return Integer.valueOf(argsSize);
+		return argsSize;
 	}
 
 	@Override
-	public Object visitVarFormalParameter(VarFormalParameter ast, Object o) {
-		Frame frame = (Frame) o;
+	public Integer visitVarFormalParameter(VarFormalParameter ast, Frame frame) {
 		ast.T.visit(this);
-		ast.entity = new UnknownAddress(Machine.addressSize, frame.level, -frame.size - Machine.addressSize);
+		ast.entity = new UnknownAddress(Machine.addressSize, frame.getLevel(), -frame.getSize() - Machine.addressSize);
 		writeTableDetails(ast);
-		return Integer.valueOf(Machine.addressSize);
+		return Machine.addressSize;
 	}
 
 	@Override
-	public Object visitEmptyFormalParameterSequence(EmptyFormalParameterSequence ast, Object o) {
-		return Integer.valueOf(0);
+	public Integer visitEmptyFormalParameterSequence(EmptyFormalParameterSequence ast, Frame frame) {
+		return 0;
 	}
 
 	@Override
-	public Object visitMultipleFormalParameterSequence(MultipleFormalParameterSequence ast, Object o) {
-		Frame frame = (Frame) o;
-		int argsSize1 = ((Integer) ast.FPS.visit(this, frame)).intValue();
-		Frame frame1 = new Frame(frame, argsSize1);
-		int argsSize2 = ((Integer) ast.FP.visit(this, frame1)).intValue();
-		return Integer.valueOf(argsSize1 + argsSize2);
+	public Integer visitMultipleFormalParameterSequence(MultipleFormalParameterSequence ast, Frame frame) {
+		var argsSize1 = ast.FPS.visit(this, frame);
+		var frame1 = frame.expand(argsSize1);
+		var argsSize2 = ast.FP.visit(this, frame1);
+		return argsSize1 + argsSize2;
 	}
 
 	@Override
-	public Object visitSingleFormalParameterSequence(SingleFormalParameterSequence ast, Object o) {
-		return ast.FP.visit(this, o);
+	public Integer visitSingleFormalParameterSequence(SingleFormalParameterSequence ast, Frame frame) {
+		return ast.FP.visit(this, frame);
 	}
 
 	// Actual Parameters
 	@Override
-	public Object visitConstActualParameter(ConstActualParameter ast, Object o) {
-		return ast.E.visit(this, o);
+	public Integer visitConstActualParameter(ConstActualParameter ast, Frame frame) {
+		return ast.E.visit(this, frame);
 	}
 
 	@Override
-	public Object visitFuncActualParameter(FuncActualParameter ast, Object o) {
-		Frame frame = (Frame) o;
+	public Integer visitFuncActualParameter(FuncActualParameter ast, Frame frame) {
 		if (ast.I.decl.entity instanceof KnownRoutine) {
-			ObjectAddress address = ((KnownRoutine) ast.I.decl.entity).address;
+			var address = ((KnownRoutine) ast.I.decl.entity).getAddress();
 			// static link, code address
-			emit(Machine.LOADAop, 0, displayRegister(frame.level, address.level), 0);
-			emit(Machine.LOADAop, 0, Machine.CBr, address.displacement);
+			emitter.emit(OpCode.LOADA, 0, frame.getDisplayRegister(address), 0);
+			emitter.emit(OpCode.LOADA, 0, Register.CB, address.getDisplacement());
 		} else if (ast.I.decl.entity instanceof UnknownRoutine) {
-			ObjectAddress address = ((UnknownRoutine) ast.I.decl.entity).address;
-			emit(Machine.LOADop, Machine.closureSize, displayRegister(frame.level, address.level),
-					address.displacement);
+			var address = ((UnknownRoutine) ast.I.decl.entity).getAddress();
+			emitter.emit(OpCode.LOAD, Machine.closureSize, frame.getDisplayRegister(address),
+					address.getDisplacement());
 		} else if (ast.I.decl.entity instanceof PrimitiveRoutine) {
-			int displacement = ((PrimitiveRoutine) ast.I.decl.entity).displacement;
+			var primitive = ((PrimitiveRoutine) ast.I.decl.entity).getPrimitive();
 			// static link, code address
-			emit(Machine.LOADAop, 0, Machine.SBr, 0);
-			emit(Machine.LOADAop, 0, Machine.PBr, displacement);
+			emitter.emit(OpCode.LOADA, 0, Register.SB, 0);
+			emitter.emit(OpCode.LOADA, Register.PB, primitive);
 		}
-		return Integer.valueOf(Machine.closureSize);
+		return Machine.closureSize;
 	}
 
 	@Override
-	public Object visitProcActualParameter(ProcActualParameter ast, Object o) {
-		Frame frame = (Frame) o;
+	public Integer visitProcActualParameter(ProcActualParameter ast, Frame frame) {
 		if (ast.I.decl.entity instanceof KnownRoutine) {
-			ObjectAddress address = ((KnownRoutine) ast.I.decl.entity).address;
+			var address = ((KnownRoutine) ast.I.decl.entity).getAddress();
 			// static link, code address
-			emit(Machine.LOADAop, 0, displayRegister(frame.level, address.level), 0);
-			emit(Machine.LOADAop, 0, Machine.CBr, address.displacement);
+			emitter.emit(OpCode.LOADA, 0, frame.getDisplayRegister(address), 0);
+			emitter.emit(OpCode.LOADA, 0, Register.CB, address.getDisplacement());
 		} else if (ast.I.decl.entity instanceof UnknownRoutine) {
-			ObjectAddress address = ((UnknownRoutine) ast.I.decl.entity).address;
-			emit(Machine.LOADop, Machine.closureSize, displayRegister(frame.level, address.level),
-					address.displacement);
+			var address = ((UnknownRoutine) ast.I.decl.entity).getAddress();
+			emitter.emit(OpCode.LOAD, Machine.closureSize, frame.getDisplayRegister(address),
+					address.getDisplacement());
 		} else if (ast.I.decl.entity instanceof PrimitiveRoutine) {
-			int displacement = ((PrimitiveRoutine) ast.I.decl.entity).displacement;
+			var primitive = ((PrimitiveRoutine) ast.I.decl.entity).getPrimitive();
 			// static link, code address
-			emit(Machine.LOADAop, 0, Machine.SBr, 0);
-			emit(Machine.LOADAop, 0, Machine.PBr, displacement);
+			emitter.emit(OpCode.LOADA, 0, Register.SB, 0);
+			emitter.emit(OpCode.LOADA, Register.PB, primitive);
 		}
-		return Integer.valueOf(Machine.closureSize);
+		return Machine.closureSize;
 	}
 
 	@Override
-	public Object visitVarActualParameter(VarActualParameter ast, Object o) {
-		encodeFetchAddress(ast.V, (Frame) o);
-		return Integer.valueOf(Machine.addressSize);
+	public Integer visitVarActualParameter(VarActualParameter ast, Frame frame) {
+		encodeFetchAddress(ast.V, frame);
+		return Machine.addressSize;
 	}
 
 	@Override
-	public Object visitEmptyActualParameterSequence(EmptyActualParameterSequence ast, Object o) {
-		return Integer.valueOf(0);
+	public Integer visitEmptyActualParameterSequence(EmptyActualParameterSequence ast, Frame frame) {
+		return 0;
 	}
 
 	@Override
-	public Object visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, Object o) {
-		Frame frame = (Frame) o;
-		int argsSize1 = ((Integer) ast.AP.visit(this, frame)).intValue();
-		Frame frame1 = new Frame(frame, argsSize1);
-		int argsSize2 = ((Integer) ast.APS.visit(this, frame1)).intValue();
-		return Integer.valueOf(argsSize1 + argsSize2);
+	public Integer visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, Frame frame) {
+		var argsSize1 = ast.AP.visit(this, frame);
+		var frame1 = frame.expand(argsSize1);
+		var argsSize2 = ast.APS.visit(this, frame1);
+		return argsSize1 + argsSize2;
 	}
 
 	@Override
-	public Object visitSingleActualParameterSequence(SingleActualParameterSequence ast, Object o) {
-		return ast.AP.visit(this, o);
+	public Integer visitSingleActualParameterSequence(SingleActualParameterSequence ast, Frame frame) {
+		return ast.AP.visit(this, frame);
 	}
 
 	// Type Denoters
 	@Override
-	public Object visitAnyTypeDenoter(AnyTypeDenoter ast, Object o) {
-		return Integer.valueOf(0);
+	public Integer visitAnyTypeDenoter(AnyTypeDenoter ast, Frame frame) {
+		return 0;
 	}
 
 	@Override
-	public Object visitArrayTypeDenoter(ArrayTypeDenoter ast, Object o) {
+	public Integer visitArrayTypeDenoter(ArrayTypeDenoter ast, Frame frame) {
 		int typeSize;
 		if (ast.entity == null) {
-			int elemSize = ((Integer) ast.T.visit(this)).intValue();
+			var elemSize = ast.T.visit(this);
 			typeSize = Integer.parseInt(ast.IL.spelling) * elemSize;
 			ast.entity = new TypeRepresentation(typeSize);
 			writeTableDetails(ast);
-		} else
-			typeSize = ast.entity.size;
-		return Integer.valueOf(typeSize);
+		} else {
+			typeSize = ast.entity.getSize();
+		}
+		return typeSize;
 	}
 
 	@Override
-	public Object visitBoolTypeDenoter(BoolTypeDenoter ast, Object o) {
+	public Integer visitBoolTypeDenoter(BoolTypeDenoter ast, Frame frame) {
 		if (ast.entity == null) {
 			ast.entity = new TypeRepresentation(Machine.booleanSize);
 			writeTableDetails(ast);
 		}
-		return Integer.valueOf(Machine.booleanSize);
+		return Machine.booleanSize;
 	}
 
 	@Override
-	public Object visitCharTypeDenoter(CharTypeDenoter ast, Object o) {
+	public Integer visitCharTypeDenoter(CharTypeDenoter ast, Frame frame) {
 		if (ast.entity == null) {
 			ast.entity = new TypeRepresentation(Machine.characterSize);
 			writeTableDetails(ast);
 		}
-		return Integer.valueOf(Machine.characterSize);
+		return Machine.characterSize;
 	}
 
 	@Override
-	public Object visitErrorTypeDenoter(ErrorTypeDenoter ast, Object o) {
-		return Integer.valueOf(0);
+	public Integer visitErrorTypeDenoter(ErrorTypeDenoter ast, Frame frame) {
+		return 0;
 	}
 
 	@Override
-	public Object visitSimpleTypeDenoter(SimpleTypeDenoter ast, Object o) {
-		return Integer.valueOf(0);
+	public Integer visitSimpleTypeDenoter(SimpleTypeDenoter ast, Frame frame) {
+		return 0;
 	}
 
 	@Override
-	public Object visitIntTypeDenoter(IntTypeDenoter ast, Object o) {
+	public Integer visitIntTypeDenoter(IntTypeDenoter ast, Frame frame) {
 		if (ast.entity == null) {
 			ast.entity = new TypeRepresentation(Machine.integerSize);
 			writeTableDetails(ast);
 		}
-		return Integer.valueOf(Machine.integerSize);
+		return Machine.integerSize;
 	}
 
 	@Override
-	public Object visitRecordTypeDenoter(RecordTypeDenoter ast, Object o) {
+	public Integer visitRecordTypeDenoter(RecordTypeDenoter ast, Frame frame) {
 		int typeSize;
 		if (ast.entity == null) {
-			typeSize = ((Integer) ast.FT.visit(this, Integer.valueOf(0))).intValue();
+			typeSize = ast.FT.visit(this, null);
 			ast.entity = new TypeRepresentation(typeSize);
 			writeTableDetails(ast);
-		} else
-			typeSize = ast.entity.size;
-		return Integer.valueOf(typeSize);
+		} else {
+			typeSize = ast.entity.getSize();
+		}
+		return typeSize;
 	}
 
 	@Override
-	public Object visitMultipleFieldTypeDenoter(MultipleFieldTypeDenoter ast, Object o) {
-		int offset = ((Integer) o).intValue();
+	public Integer visitMultipleFieldTypeDenoter(MultipleFieldTypeDenoter ast, Frame frame) {
+		var offset = frame.getSize();
 		int fieldSize;
-
 		if (ast.entity == null) {
-			fieldSize = ((Integer) ast.T.visit(this)).intValue();
+			fieldSize = ast.T.visit(this);
 			ast.entity = new Field(fieldSize, offset);
 			writeTableDetails(ast);
-		} else
-			fieldSize = ast.entity.size;
+		} else {
+			fieldSize = ast.entity.getSize();
+		}
 
-		Integer offset1 = Integer.valueOf(offset + fieldSize);
-		int recSize = ((Integer) ast.FT.visit(this, offset1)).intValue();
-		return Integer.valueOf(fieldSize + recSize);
+		var offset1 = frame.replace(offset + fieldSize);
+		var recSize = ast.FT.visit(this, offset1);
+		return fieldSize + recSize;
 	}
 
 	@Override
-	public Object visitSingleFieldTypeDenoter(SingleFieldTypeDenoter ast, Object o) {
-		int offset = ((Integer) o).intValue();
+	public Integer visitSingleFieldTypeDenoter(SingleFieldTypeDenoter ast, Frame frame) {
+		var offset = frame.getSize();
 		int fieldSize;
-
 		if (ast.entity == null) {
-			fieldSize = ((Integer) ast.T.visit(this)).intValue();
+			fieldSize = ast.T.visit(this);
 			ast.entity = new Field(fieldSize, offset);
 			writeTableDetails(ast);
-		} else
-			fieldSize = ast.entity.size;
+		} else {
+			fieldSize = ast.entity.getSize();
+		}
 
-		return Integer.valueOf(fieldSize);
+		return fieldSize;
 	}
 
 	// Literals, Identifiers and Operators
 	@Override
-	public Object visitCharacterLiteral(CharacterLiteral ast, Object o) {
+	public Void visitCharacterLiteral(CharacterLiteral ast, Void arg) {
 		return null;
 	}
 
 	@Override
-	public Object visitIdentifier(Identifier ast, Object o) {
-		Frame frame = (Frame) o;
+	public Void visitIdentifier(Identifier ast, Frame frame) {
 		if (ast.decl.entity instanceof KnownRoutine) {
-			ObjectAddress address = ((KnownRoutine) ast.decl.entity).address;
-			emit(Machine.CALLop, displayRegister(frame.level, address.level), Machine.CBr, address.displacement);
+			var address = ((KnownRoutine) ast.decl.entity).getAddress();
+			emitter.emit(OpCode.CALL, frame.getDisplayRegister(address), Register.CB, address.getDisplacement());
 		} else if (ast.decl.entity instanceof UnknownRoutine) {
-			ObjectAddress address = ((UnknownRoutine) ast.decl.entity).address;
-			emit(Machine.LOADop, Machine.closureSize, displayRegister(frame.level, address.level),
-					address.displacement);
-			emit(Machine.CALLIop, 0, 0, 0);
+			var address = ((UnknownRoutine) ast.decl.entity).getAddress();
+			emitter.emit(OpCode.LOAD, Machine.closureSize, frame.getDisplayRegister(address),
+					address.getDisplacement());
+			emitter.emit(OpCode.CALLI, 0);
 		} else if (ast.decl.entity instanceof PrimitiveRoutine) {
-			int displacement = ((PrimitiveRoutine) ast.decl.entity).displacement;
-			if (displacement != Machine.idDisplacement)
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, displacement);
+			var primitive = ((PrimitiveRoutine) ast.decl.entity).getPrimitive();
+			if (primitive != Primitive.ID)
+				emitter.emit(OpCode.CALL, Register.PB, primitive);
 		} else if (ast.decl.entity instanceof EqualityRoutine) { // "=" or "\="
-			int displacement = ((EqualityRoutine) ast.decl.entity).displacement;
-			emit(Machine.LOADLop, 0, 0, frame.size / 2);
-			emit(Machine.CALLop, Machine.SBr, Machine.PBr, displacement);
+			var primitive = ((EqualityRoutine) ast.decl.entity).getPrimitive();
+			emitter.emit(OpCode.LOADL, 0, frame.getSize() / 2);
+			emitter.emit(OpCode.CALL, Register.PB, primitive);
 		}
 		return null;
 	}
 
 	@Override
-	public Object visitIntegerLiteral(IntegerLiteral ast, Object o) {
+	public Void visitIntegerLiteral(IntegerLiteral ast, Void arg) {
 		return null;
 	}
 
 	@Override
-	public Object visitOperator(Operator ast, Object o) {
-		Frame frame = (Frame) o;
+	public Void visitOperator(Operator ast, Frame frame) {
 		if (ast.decl.entity instanceof KnownRoutine) {
-			ObjectAddress address = ((KnownRoutine) ast.decl.entity).address;
-			emit(Machine.CALLop, displayRegister(frame.level, address.level), Machine.CBr, address.displacement);
+			var address = ((KnownRoutine) ast.decl.entity).getAddress();
+			emitter.emit(OpCode.CALL, frame.getDisplayRegister(address), Register.CB, address.getDisplacement());
 		} else if (ast.decl.entity instanceof UnknownRoutine) {
-			ObjectAddress address = ((UnknownRoutine) ast.decl.entity).address;
-			emit(Machine.LOADop, Machine.closureSize, displayRegister(frame.level, address.level),
-					address.displacement);
-			emit(Machine.CALLIop, 0, 0, 0);
+			var address = ((UnknownRoutine) ast.decl.entity).getAddress();
+			emitter.emit(OpCode.LOAD, Machine.closureSize, frame.getDisplayRegister(address),
+					address.getDisplacement());
+			emitter.emit(OpCode.CALLI, 0);
 		} else if (ast.decl.entity instanceof PrimitiveRoutine) {
-			int displacement = ((PrimitiveRoutine) ast.decl.entity).displacement;
-			if (displacement != Machine.idDisplacement)
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, displacement);
+			var primitive = ((PrimitiveRoutine) ast.decl.entity).getPrimitive();
+			if (primitive != Primitive.ID)
+				emitter.emit(OpCode.CALL, Register.PB, primitive);
 		} else if (ast.decl.entity instanceof EqualityRoutine) { // "=" or "\="
-			int displacement = ((EqualityRoutine) ast.decl.entity).displacement;
-			emit(Machine.LOADLop, 0, 0, frame.size / 2);
-			emit(Machine.CALLop, Machine.SBr, Machine.PBr, displacement);
+			var primitive = ((EqualityRoutine) ast.decl.entity).getPrimitive();
+			emitter.emit(OpCode.LOADL, 0, frame.getSize() / 2);
+			emitter.emit(OpCode.CALL, Register.PB, primitive);
 		}
 		return null;
 	}
 
 	// Value-or-variable names
 	@Override
-	public Object visitDotVname(DotVname ast, Object o) {
-		Frame frame = (Frame) o;
-		RuntimeEntity baseObject = (RuntimeEntity) ast.V.visit(this, frame);
-		ast.offset = ast.V.offset + ((Field) ast.I.decl.entity).fieldOffset;
+	public RuntimeEntity visitDotVname(DotVname ast, Frame frame) {
+		var baseObject = ast.V.visit(this, frame);
+		ast.offset = ast.V.offset + ((Field) ast.I.decl.entity).getFieldOffset();
 		// I.decl points to the appropriate record field
 		ast.indexed = ast.V.indexed;
 		return baseObject;
 	}
 
 	@Override
-	public Object visitSimpleVname(SimpleVname ast, Object o) {
+	public RuntimeEntity visitSimpleVname(SimpleVname ast, Frame frame) {
 		ast.offset = 0;
 		ast.indexed = false;
 		return ast.I.decl.entity;
 	}
 
 	@Override
-	public Object visitSubscriptVname(SubscriptVname ast, Object o) {
-		Frame frame = (Frame) o;
-		RuntimeEntity baseObject;
-		int elemSize, indexSize;
-
-		baseObject = (RuntimeEntity) ast.V.visit(this, frame);
+	public RuntimeEntity visitSubscriptVname(SubscriptVname ast, Frame frame) {
+		var baseObject = ast.V.visit(this, frame);
 		ast.offset = ast.V.offset;
 		ast.indexed = ast.V.indexed;
-		elemSize = ((Integer) ast.type.visit(this)).intValue();
+		var elemSize = ast.type.visit(this);
 		if (ast.E instanceof IntegerExpression) {
-			IntegerLiteral IL = ((IntegerExpression) ast.E).IL;
+			var IL = ((IntegerExpression) ast.E).IL;
 			ast.offset = ast.offset + Integer.parseInt(IL.spelling) * elemSize;
 		} else {
 			// v-name is indexed by a proper expression, not a literal
-			if (ast.indexed)
-				frame.size = frame.size + Machine.integerSize;
-			indexSize = ((Integer) ast.E.visit(this, frame)).intValue();
+			if (ast.indexed) {
+				frame = frame.expand(Machine.integerSize);
+			}
+			ast.E.visit(this, frame);
 			if (elemSize != 1) {
-				emit(Machine.LOADLop, 0, 0, elemSize);
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.multDisplacement);
+				emitter.emit(OpCode.LOADL, 0, elemSize);
+				emitter.emit(OpCode.CALL, Register.PB, Primitive.MULT);
 			}
 			if (ast.indexed)
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-			else
+				emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+			else {
 				ast.indexed = true;
+			}
 		}
 		return baseObject;
 	}
 
 	// Programs
 	@Override
-	public Object visitProgram(Program ast, Object o) {
-		return ast.C.visit(this, o);
+	public Void visitProgram(Program ast, Frame frame) {
+		return ast.C.visit(this, frame);
 	}
 
-	public Encoder(ErrorReporter reporter) {
+	public Encoder(Emitter emitter, ErrorReporter reporter) {
+		this.emitter = emitter;
 		this.reporter = reporter;
-		nextInstrAddr = Machine.CB;
+
 		elaborateStdEnvironment();
 	}
 
+	private Emitter emitter;
+
 	private ErrorReporter reporter;
 
 	// Generates code to run a program.
 	// showingTable is true iff entity description details
 	// are to be displayed.
-	public final void encodeRun(Program theAST, boolean showingTable) {
+	public final void encodeRun(Program program, boolean showingTable) {
 		tableDetailsReqd = showingTable;
 		// startCodeGeneration();
-		theAST.visit(this, new Frame(0, 0));
-		emit(Machine.HALTop, 0, 0, 0);
+		program.visit(this, Frame.Initial);
+		emitter.emit(OpCode.HALT);
 	}
 
 	// Decides run-time representation of a standard constant.
 	private final void elaborateStdConst(Declaration constDeclaration, int value) {
 
 		if (constDeclaration instanceof ConstDeclaration) {
-			ConstDeclaration decl = (ConstDeclaration) constDeclaration;
-			int typeSize = ((Integer) decl.E.type.visit(this)).intValue();
+			var decl = (ConstDeclaration) constDeclaration;
+			var typeSize = decl.E.type.visit(this);
 			decl.entity = new KnownValue(typeSize, value);
 			writeTableDetails(constDeclaration);
 		}
 	}
 
 	// Decides run-time representation of a standard routine.
-	private final void elaborateStdPrimRoutine(Declaration routineDeclaration, int routineOffset) {
-		routineDeclaration.entity = new PrimitiveRoutine(Machine.closureSize, routineOffset);
+	private final void elaborateStdPrimRoutine(Declaration routineDeclaration, Primitive primitive) {
+		routineDeclaration.entity = new PrimitiveRoutine(Machine.closureSize, primitive);
 		writeTableDetails(routineDeclaration);
 	}
 
-	private final void elaborateStdEqRoutine(Declaration routineDeclaration, int routineOffset) {
-		routineDeclaration.entity = new EqualityRoutine(Machine.closureSize, routineOffset);
+	private final void elaborateStdEqRoutine(Declaration routineDeclaration, Primitive primitive) {
+		routineDeclaration.entity = new EqualityRoutine(Machine.closureSize, primitive);
 		writeTableDetails(routineDeclaration);
 	}
 
@@ -790,114 +775,36 @@ public final class Encoder implements Visitor {
 		tableDetailsReqd = false;
 		elaborateStdConst(StdEnvironment.falseDecl, Machine.falseRep);
 		elaborateStdConst(StdEnvironment.trueDecl, Machine.trueRep);
-		elaborateStdPrimRoutine(StdEnvironment.notDecl, Machine.notDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.andDecl, Machine.andDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.orDecl, Machine.orDisplacement);
+		elaborateStdPrimRoutine(StdEnvironment.notDecl, Primitive.NOT);
+		elaborateStdPrimRoutine(StdEnvironment.andDecl, Primitive.AND);
+		elaborateStdPrimRoutine(StdEnvironment.orDecl, Primitive.OR);
 		elaborateStdConst(StdEnvironment.maxintDecl, Machine.maxintRep);
-		elaborateStdPrimRoutine(StdEnvironment.addDecl, Machine.addDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.subtractDecl, Machine.subDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.multiplyDecl, Machine.multDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.divideDecl, Machine.divDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.moduloDecl, Machine.modDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.lessDecl, Machine.ltDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.notgreaterDecl, Machine.leDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.greaterDecl, Machine.gtDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.notlessDecl, Machine.geDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.chrDecl, Machine.idDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.ordDecl, Machine.idDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.eolDecl, Machine.eolDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.eofDecl, Machine.eofDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.getDecl, Machine.getDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.putDecl, Machine.putDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.getintDecl, Machine.getintDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.putintDecl, Machine.putintDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.geteolDecl, Machine.geteolDisplacement);
-		elaborateStdPrimRoutine(StdEnvironment.puteolDecl, Machine.puteolDisplacement);
-		elaborateStdEqRoutine(StdEnvironment.equalDecl, Machine.eqDisplacement);
-		elaborateStdEqRoutine(StdEnvironment.unequalDecl, Machine.neDisplacement);
-	}
-
-	// Saves the object program in the named file.
-
-	public void saveObjectProgram(String objectName) {
-		FileOutputStream objectFile = null;
-		DataOutputStream objectStream = null;
-
-		int addr;
-
-		try {
-			objectFile = new FileOutputStream(objectName);
-			objectStream = new DataOutputStream(objectFile);
-
-			addr = Machine.CB;
-			for (addr = Machine.CB; addr < nextInstrAddr; addr++)
-				Machine.code[addr].write(objectStream);
-			objectFile.close();
-		} catch (FileNotFoundException s) {
-			System.err.println("Error opening object file: " + s);
-		} catch (IOException s) {
-			System.err.println("Error writing object file: " + s);
-		}
+		elaborateStdPrimRoutine(StdEnvironment.addDecl, Primitive.ADD);
+		elaborateStdPrimRoutine(StdEnvironment.subtractDecl, Primitive.SUB);
+		elaborateStdPrimRoutine(StdEnvironment.multiplyDecl, Primitive.MULT);
+		elaborateStdPrimRoutine(StdEnvironment.divideDecl, Primitive.DIV);
+		elaborateStdPrimRoutine(StdEnvironment.moduloDecl, Primitive.MOD);
+		elaborateStdPrimRoutine(StdEnvironment.lessDecl, Primitive.LT);
+		elaborateStdPrimRoutine(StdEnvironment.notgreaterDecl, Primitive.LE);
+		elaborateStdPrimRoutine(StdEnvironment.greaterDecl, Primitive.GT);
+		elaborateStdPrimRoutine(StdEnvironment.notlessDecl, Primitive.GE);
+		elaborateStdPrimRoutine(StdEnvironment.chrDecl, Primitive.ID);
+		elaborateStdPrimRoutine(StdEnvironment.ordDecl, Primitive.ID);
+		elaborateStdPrimRoutine(StdEnvironment.eolDecl, Primitive.EOL);
+		elaborateStdPrimRoutine(StdEnvironment.eofDecl, Primitive.EOF);
+		elaborateStdPrimRoutine(StdEnvironment.getDecl, Primitive.GET);
+		elaborateStdPrimRoutine(StdEnvironment.putDecl, Primitive.PUT);
+		elaborateStdPrimRoutine(StdEnvironment.getintDecl, Primitive.GETINT);
+		elaborateStdPrimRoutine(StdEnvironment.putintDecl, Primitive.PUTINT);
+		elaborateStdPrimRoutine(StdEnvironment.geteolDecl, Primitive.GETEOL);
+		elaborateStdPrimRoutine(StdEnvironment.puteolDecl, Primitive.PUTEOL);
+		elaborateStdEqRoutine(StdEnvironment.equalDecl, Primitive.EQ);
+		elaborateStdEqRoutine(StdEnvironment.unequalDecl, Primitive.NE);
 	}
 
 	boolean tableDetailsReqd;
 
-	public static void writeTableDetails(AST ast) {
-	}
-
-	// OBJECT CODE
-
-	// Implementation notes:
-	// Object code is generated directly into the TAM Code Store, starting at CB.
-	// The address of the next instruction is held in nextInstrAddr.
-
-	private int nextInstrAddr;
-
-	// Appends an instruction, with the given fields, to the object code.
-	private void emit(int op, int n, int r, int d) {
-		Instruction nextInstr = new Instruction();
-		if (n > 255) {
-			reporter.reportRestriction("length of operand can't exceed 255 words");
-			n = 255; // to allow code generation to continue
-		}
-		nextInstr.op = op;
-		nextInstr.n = n;
-		nextInstr.r = r;
-		nextInstr.d = d;
-		if (nextInstrAddr == Machine.PB)
-			reporter.reportRestriction("too many instructions for code segment");
-		else {
-			Machine.code[nextInstrAddr] = nextInstr;
-			nextInstrAddr = nextInstrAddr + 1;
-		}
-	}
-
-	// Patches the d-field of the instruction at address addr.
-	private void patch(int addr, int d) {
-		Machine.code[addr].d = d;
-	}
-
-	// DATA REPRESENTATION
-
-	public int characterValuation(String spelling) {
-		// Returns the machine representation of the given character literal.
-		return spelling.charAt(1);
-		// since the character literal is of the form 'x'}
-	}
-
-	// REGISTERS
-
-	// Returns the register number appropriate for object code at currentLevel
-	// to address a data object at objectLevel.
-	private int displayRegister(int currentLevel, int objectLevel) {
-		if (objectLevel == 0)
-			return Machine.SBr;
-		else if (currentLevel - objectLevel <= 6)
-			return Machine.LBr + currentLevel - objectLevel; // LBr|L1r|...|L6r
-		else {
-			reporter.reportRestriction("can't access data more than 6 levels out");
-			return Machine.L6r; // to allow code generation to continue
-		}
+	public static void writeTableDetails(AbstractSyntaxTree ast) {
 	}
 
 	// Generates code to fetch the value of a named constant or variable
@@ -909,34 +816,14 @@ public final class Encoder implements Visitor {
 
 	private void encodeStore(Vname V, Frame frame, int valSize) {
 
-		RuntimeEntity baseObject = (RuntimeEntity) V.visit(this, frame);
+		var baseObject = (AddressableEntity) V.visit(this, frame);
 		// If indexed = true, code will have been generated to load an index value.
 		if (valSize > 255) {
 			reporter.reportRestriction("can't store values larger than 255 words");
 			valSize = 255; // to allow code generation to continue
 		}
-		if (baseObject instanceof KnownAddress) {
-			ObjectAddress address = ((KnownAddress) baseObject).address;
-			if (V.indexed) {
-				emit(Machine.LOADAop, 0, displayRegister(frame.level, address.level), address.displacement + V.offset);
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-				emit(Machine.STOREIop, valSize, 0, 0);
-			} else {
-				emit(Machine.STOREop, valSize, displayRegister(frame.level, address.level),
-						address.displacement + V.offset);
-			}
-		} else if (baseObject instanceof UnknownAddress) {
-			ObjectAddress address = ((UnknownAddress) baseObject).address;
-			emit(Machine.LOADop, Machine.addressSize, displayRegister(frame.level, address.level),
-					address.displacement);
-			if (V.indexed)
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-			if (V.offset != 0) {
-				emit(Machine.LOADLop, 0, 0, V.offset);
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-			}
-			emit(Machine.STOREIop, valSize, 0, 0);
-		}
+
+		baseObject.encodeStore(emitter, frame, valSize, V);
 	}
 
 	// Generates code to fetch the value of a named constant or variable
@@ -948,38 +835,14 @@ public final class Encoder implements Visitor {
 
 	private void encodeFetch(Vname V, Frame frame, int valSize) {
 
-		RuntimeEntity baseObject = (RuntimeEntity) V.visit(this, frame);
+		var baseObject = (FetchableEntity) V.visit(this, frame);
 		// If indexed = true, code will have been generated to load an index value.
 		if (valSize > 255) {
 			reporter.reportRestriction("can't load values larger than 255 words");
 			valSize = 255; // to allow code generation to continue
 		}
-		if (baseObject instanceof KnownValue) {
-			// presumably offset = 0 and indexed = false
-			int value = ((KnownValue) baseObject).value;
-			emit(Machine.LOADLop, 0, 0, value);
-		} else if ((baseObject instanceof UnknownValue) || (baseObject instanceof KnownAddress)) {
-			ObjectAddress address = (baseObject instanceof UnknownValue) ? ((UnknownValue) baseObject).address
-					: ((KnownAddress) baseObject).address;
-			if (V.indexed) {
-				emit(Machine.LOADAop, 0, displayRegister(frame.level, address.level), address.displacement + V.offset);
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-				emit(Machine.LOADIop, valSize, 0, 0);
-			} else
-				emit(Machine.LOADop, valSize, displayRegister(frame.level, address.level),
-						address.displacement + V.offset);
-		} else if (baseObject instanceof UnknownAddress) {
-			ObjectAddress address = ((UnknownAddress) baseObject).address;
-			emit(Machine.LOADop, Machine.addressSize, displayRegister(frame.level, address.level),
-					address.displacement);
-			if (V.indexed)
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-			if (V.offset != 0) {
-				emit(Machine.LOADLop, 0, 0, V.offset);
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-			}
-			emit(Machine.LOADIop, valSize, 0, 0);
-		}
+
+		baseObject.encodeFetch(emitter, frame, valSize, V);
 	}
 
 	// Generates code to compute and push the address of a named variable.
@@ -990,23 +853,7 @@ public final class Encoder implements Visitor {
 
 	private void encodeFetchAddress(Vname V, Frame frame) {
 
-		RuntimeEntity baseObject = (RuntimeEntity) V.visit(this, frame);
-		// If indexed = true, code will have been generated to load an index value.
-		if (baseObject instanceof KnownAddress) {
-			ObjectAddress address = ((KnownAddress) baseObject).address;
-			emit(Machine.LOADAop, 0, displayRegister(frame.level, address.level), address.displacement + V.offset);
-			if (V.indexed)
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-		} else if (baseObject instanceof UnknownAddress) {
-			ObjectAddress address = ((UnknownAddress) baseObject).address;
-			emit(Machine.LOADop, Machine.addressSize, displayRegister(frame.level, address.level),
-					address.displacement);
-			if (V.indexed)
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-			if (V.offset != 0) {
-				emit(Machine.LOADLop, 0, 0, V.offset);
-				emit(Machine.CALLop, Machine.SBr, Machine.PBr, Machine.addDisplacement);
-			}
-		}
+		var baseObject = (AddressableEntity) V.visit(this, frame);
+		baseObject.encodeFetchAddress(emitter, frame, V);
 	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/AddressableEntity.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/AddressableEntity.java
new file mode 100644
index 0000000..96ca554
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/AddressableEntity.java
@@ -0,0 +1,29 @@
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public abstract class AddressableEntity extends RuntimeEntity implements FetchableEntity {
+
+	protected final ObjectAddress address;
+
+	protected AddressableEntity(int size, int level, int displacement) {
+		super(size);
+		address = new ObjectAddress(level, displacement);
+	}
+
+	protected AddressableEntity(int size, Frame frame) {
+		this(size, frame.getLevel(), frame.getSize());
+	}
+
+	public ObjectAddress getAddress() {
+		return address;
+	}
+
+	public abstract void encodeStore(Emitter emitter, Frame frame, int size, Vname vname);
+
+	public abstract void encodeFetchAddress(Emitter emitter, Frame frame, Vname vname);
+
+	public abstract void encodeFetch(Emitter emitter, Frame frame, int size, Vname vname);
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/EqualityRoutine.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/EqualityRoutine.java
new file mode 100644
index 0000000..0ff2774
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/EqualityRoutine.java
@@ -0,0 +1,46 @@
+/*
+ * @(#)EqualityRoutine.java                        2.1 2003/10/07
+ *
+ * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
+ * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
+ * and School of Computer and Math Sciences, The Robert Gordon University,
+ * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
+ * All rights reserved.
+ *
+ * This software is provided free for educational use only. It may
+ * not be used for commercial purposes without the prior written permission
+ * of the authors.
+ */
+
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.AbstractMachine.OpCode;
+import Triangle.AbstractMachine.Primitive;
+import Triangle.AbstractMachine.Register;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public class EqualityRoutine extends RuntimeEntity implements RoutineEntity {
+
+	private final Primitive primitive;
+
+	public EqualityRoutine(int size, Primitive primitive) {
+		super(size);
+		this.primitive = primitive;
+	}
+
+	public final Primitive getPrimitive() {
+		return primitive;
+	}
+
+	public void encodeCall(Emitter emitter, Frame frame) {
+		emitter.emit(OpCode.LOADL, frame.getSize() / 2);
+		emitter.emit(OpCode.CALL, Register.PB, primitive);
+	}
+
+	public void encodeFetch(Emitter emitter, Frame frame) {
+		emitter.emit(OpCode.LOADA, 0, Register.SB, 0);
+		emitter.emit(OpCode.LOADA, Register.PB, primitive);
+	}
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/FetchableEntity.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/FetchableEntity.java
new file mode 100644
index 0000000..c573dfc
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/FetchableEntity.java
@@ -0,0 +1,11 @@
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public interface FetchableEntity {
+
+    void encodeFetch(Emitter emitter, Frame frame, int size, Vname vname);
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Field.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/Field.java
similarity index 83%
rename from Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Field.java
rename to Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/Field.java
index 7906945..ba7c120 100644
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Field.java
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/Field.java
@@ -12,20 +12,18 @@
  * of the authors.
  */
 
-package Triangle.CodeGenerator;
+package Triangle.CodeGenerator.Entities;
 
 public class Field extends RuntimeEntity {
 
-	public Field() {
-		super();
-		fieldOffset = 0;
-	}
+	private final int fieldOffset;
 
 	public Field(int size, int fieldOffset) {
 		super(size);
 		this.fieldOffset = fieldOffset;
 	}
 
-	public int fieldOffset;
-
+	public final int getFieldOffset() {
+		return fieldOffset;
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/KnownAddress.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/KnownAddress.java
new file mode 100644
index 0000000..7343da5
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/KnownAddress.java
@@ -0,0 +1,62 @@
+/*
+ * @(#)KnownAddress.java                        2.1 2003/10/07
+ *
+ * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
+ * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
+ * and School of Computer and Math Sciences, The Robert Gordon University,
+ * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
+ * All rights reserved.
+ *
+ * This software is provided free for educational use only. It may
+ * not be used for commercial purposes without the prior written permission
+ * of the authors.
+ */
+
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.AbstractMachine.OpCode;
+import Triangle.AbstractMachine.Primitive;
+import Triangle.AbstractMachine.Register;
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public class KnownAddress extends AddressableEntity {
+
+	public KnownAddress(int size, int level, int displacement) {
+		super(size, level, displacement);
+	}
+
+	public KnownAddress(int size, Frame frame) {
+		super(size, frame);
+	}
+
+	public void encodeStore(Emitter emitter, Frame frame, int size, Vname vname) {
+		if (vname.indexed) {
+			emitter.emit(OpCode.LOADA, 0, frame.getDisplayRegister(address), address.getDisplacement() + vname.offset);
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+			emitter.emit(OpCode.STOREI, size, 0);
+		} else {
+			emitter.emit(OpCode.STORE, size, frame.getDisplayRegister(address),
+					address.getDisplacement() + vname.offset);
+		}
+	}
+
+	public void encodeFetch(Emitter emitter, Frame frame, int size, Vname vname) {
+		if (vname.indexed) {
+			emitter.emit(OpCode.LOADA, 0, frame.getDisplayRegister(address), address.getDisplacement() + vname.offset);
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+			emitter.emit(OpCode.LOADI, size, 0);
+		} else {
+			emitter.emit(OpCode.LOAD, size, frame.getDisplayRegister(address),
+					address.getDisplacement() + vname.offset);
+		}
+	}
+
+	public void encodeFetchAddress(Emitter emitter, Frame frame, Vname vname) {
+		emitter.emit(OpCode.LOADA, 0, frame.getDisplayRegister(address), address.getDisplacement() + vname.offset);
+		if (vname.indexed) {
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+		}
+	}
+}
\ No newline at end of file
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/KnownRoutine.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/KnownRoutine.java
new file mode 100644
index 0000000..0a1c835
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/KnownRoutine.java
@@ -0,0 +1,44 @@
+/*
+ * @(#)KnownRoutine.java                        2.1 2003/10/07
+ *
+ * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
+ * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
+ * and School of Computer and Math Sciences, The Robert Gordon University,
+ * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
+ * All rights reserved.
+ *
+ * This software is provided free for educational use only. It may
+ * not be used for commercial purposes without the prior written permission
+ * of the authors.
+ */
+
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.AbstractMachine.OpCode;
+import Triangle.AbstractMachine.Register;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public class KnownRoutine extends RuntimeEntity implements RoutineEntity {
+
+	private final ObjectAddress address;
+
+	public KnownRoutine(int size, int level, int displacement) {
+		super(size);
+		address = new ObjectAddress(level, displacement);
+	}
+
+	public final ObjectAddress getAddress() {
+		return address;
+	}
+
+	public void encodeCall(Emitter emitter, Frame frame) {
+		emitter.emit(OpCode.CALL, frame.getDisplayRegister(address), Register.CB, address.getDisplacement());
+	}
+
+	public void encodeFetch(Emitter emitter, Frame frame) {
+		emitter.emit(OpCode.LOADA, frame.getDisplayRegister(address), 0);
+		emitter.emit(OpCode.LOADA, Register.CB, address.getDisplacement());
+	}
+
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/KnownValue.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/KnownValue.java
similarity index 53%
rename from Triangle.Compiler/src/main/java/Triangle/CodeGenerator/KnownValue.java
rename to Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/KnownValue.java
index 2144a6a..8de3458 100644
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/KnownValue.java
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/KnownValue.java
@@ -12,20 +12,28 @@
  * of the authors.
  */
 
-package Triangle.CodeGenerator;
+package Triangle.CodeGenerator.Entities;
 
-public class KnownValue extends RuntimeEntity {
+import Triangle.AbstractMachine.OpCode;
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
 
-	public KnownValue() {
-		super();
-		value = 0;
-	}
+public class KnownValue extends RuntimeEntity implements FetchableEntity {
+
+	private final int value;
 
 	public KnownValue(int size, int value) {
 		super(size);
 		this.value = value;
 	}
 
-	public int value;
+	public final int getValue() {
+		return value;
+	}
 
-}
+	public void encodeFetch(Emitter emitter, Frame frame, int size, Vname vname) {
+		// presumably offset = 0 and indexed = false
+		emitter.emit(OpCode.LOADL, 0, value);
+	}
+}
\ No newline at end of file
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/ObjectAddress.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/ObjectAddress.java
similarity index 72%
rename from Triangle.Compiler/src/main/java/Triangle/CodeGenerator/ObjectAddress.java
rename to Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/ObjectAddress.java
index 05df9fc..ba1eb85 100644
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/ObjectAddress.java
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/ObjectAddress.java
@@ -12,15 +12,24 @@
  * of the authors.
  */
 
-package Triangle.CodeGenerator;
+package Triangle.CodeGenerator.Entities;
 
-public final class ObjectAddress {
+public class ObjectAddress {
+
+	private final int level;
+
+	private final int displacement;
 
 	public ObjectAddress(int level, int displacement) {
 		this.level = level;
 		this.displacement = displacement;
 	}
 
-	public int level, displacement;
+	public final int getLevel() {
+		return level;
+	}
 
-}
+	public int getDisplacement() {
+		return displacement;
+	}
+}
\ No newline at end of file
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/PrimitiveRoutine.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/PrimitiveRoutine.java
new file mode 100644
index 0000000..f547a84
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/PrimitiveRoutine.java
@@ -0,0 +1,47 @@
+/*
+ * @(#)PrimitiveRoutine.java                        2.1 2003/10/07
+ *
+ * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
+ * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
+ * and School of Computer and Math Sciences, The Robert Gordon University,
+ * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
+ * All rights reserved.
+ *
+ * This software is provided free for educational use only. It may
+ * not be used for commercial purposes without the prior written permission
+ * of the authors.
+ */
+
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.AbstractMachine.OpCode;
+import Triangle.AbstractMachine.Primitive;
+import Triangle.AbstractMachine.Register;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public class PrimitiveRoutine extends RuntimeEntity implements RoutineEntity {
+
+	private final Primitive primitive;
+
+	public PrimitiveRoutine(int size, Primitive primitive) {
+		super(size);
+		this.primitive = primitive;
+	}
+
+	public final Primitive getPrimitive() {
+		return primitive;
+	}
+
+	public void encodeCall(Emitter emitter, Frame frame) {
+		if (primitive != Primitive.ID) {
+			emitter.emit(OpCode.CALL, Register.PB, primitive);
+		}
+	}
+
+	public void encodeFetch(Emitter emitter, Frame frame) {
+		emitter.emit(OpCode.LOADA, 0, Register.SB, 0);
+		emitter.emit(OpCode.LOADA, Register.PB, primitive);
+	}
+
+}
\ No newline at end of file
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/RoutineEntity.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/RoutineEntity.java
new file mode 100644
index 0000000..37884fe
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/RoutineEntity.java
@@ -0,0 +1,11 @@
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public interface RoutineEntity {
+
+	void encodeCall(Emitter emitter, Frame frame);
+
+	void encodeFetch(Emitter emitter, Frame frame);
+}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/RuntimeEntity.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/RuntimeEntity.java
similarity index 78%
rename from Triangle.Compiler/src/main/java/Triangle/CodeGenerator/RuntimeEntity.java
rename to Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/RuntimeEntity.java
index 69a1cf6..ed99d3a 100644
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/RuntimeEntity.java
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/RuntimeEntity.java
@@ -12,22 +12,19 @@
  * of the authors.
  */
 
-package Triangle.CodeGenerator;
+package Triangle.CodeGenerator.Entities;
 
 // Run-time object
 
 public abstract class RuntimeEntity {
 
-	public final static int maxRoutineLevel = 7;
+	private final int size;
 
-	public RuntimeEntity() {
-		size = 0;
-	}
-
-	public RuntimeEntity(int size) {
+	protected RuntimeEntity(int size) {
 		this.size = size;
 	}
 
-	public int size;
-
+	public final int getSize() {
+		return size;
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/TypeRepresentation.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/TypeRepresentation.java
similarity index 94%
rename from Triangle.Compiler/src/main/java/Triangle/CodeGenerator/TypeRepresentation.java
rename to Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/TypeRepresentation.java
index ebe50c0..f39bd52 100644
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/TypeRepresentation.java
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/TypeRepresentation.java
@@ -12,7 +12,7 @@
  * of the authors.
  */
 
-package Triangle.CodeGenerator;
+package Triangle.CodeGenerator.Entities;
 
 public class TypeRepresentation extends RuntimeEntity {
 
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/UnknownAddress.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/UnknownAddress.java
new file mode 100644
index 0000000..38d820b
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/UnknownAddress.java
@@ -0,0 +1,74 @@
+/*
+ * @(#)UnknownAddress.java                        2.1 2003/10/07
+ *
+ * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
+ * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
+ * and School of Computer and Math Sciences, The Robert Gordon University,
+ * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
+ * All rights reserved.
+ *
+ * This software is provided free for educational use only. It may
+ * not be used for commercial purposes without the prior written permission
+ * of the authors.
+ */
+
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.AbstractMachine.Machine;
+import Triangle.AbstractMachine.OpCode;
+import Triangle.AbstractMachine.Primitive;
+import Triangle.AbstractMachine.Register;
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public class UnknownAddress extends AddressableEntity {
+
+	public UnknownAddress(int size, int level, int displacement) {
+		super(size, level, displacement);
+	}
+
+	public void encodeStore(Emitter emitter, Frame frame, int size, Vname vname) {
+
+		emitter.emit(OpCode.LOAD, Machine.addressSize, frame.getDisplayRegister(address), address.getDisplacement());
+		if (vname.indexed) {
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+		}
+
+		int offset = vname.offset;
+		if (offset != 0) {
+			emitter.emit(OpCode.LOADL, 0, offset);
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+		}
+		emitter.emit(OpCode.STOREI, size, 0);
+	}
+
+	public void encodeFetch(Emitter emitter, Frame frame, int size, Vname vname) {
+		emitter.emit(OpCode.LOAD, Machine.addressSize, frame.getDisplayRegister(address), address.getDisplacement());
+
+		if (vname.indexed) {
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+		}
+
+		int offset = vname.offset;
+		if (offset != 0) {
+			emitter.emit(OpCode.LOADL, offset);
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+		}
+		emitter.emit(OpCode.LOADI, size);
+	}
+
+	public void encodeFetchAddress(Emitter emitter, Frame frame, Vname vname) {
+
+		emitter.emit(OpCode.LOAD, Machine.addressSize, frame.getDisplayRegister(address), address.getDisplacement());
+		if (vname.indexed) {
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+		}
+
+		int offset = vname.offset;
+		if (offset != 0) {
+			emitter.emit(OpCode.LOADL, offset);
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+		}
+	}
+}
\ No newline at end of file
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/UnknownRoutine.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/UnknownRoutine.java
new file mode 100644
index 0000000..b37b03e
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/UnknownRoutine.java
@@ -0,0 +1,44 @@
+/*
+ * @(#)UnknownRoutine.java                        2.1 2003/10/07
+ *
+ * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
+ * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
+ * and School of Computer and Math Sciences, The Robert Gordon University,
+ * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
+ * All rights reserved.
+ *
+ * This software is provided free for educational use only. It may
+ * not be used for commercial purposes without the prior written permission
+ * of the authors.
+ */
+
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.AbstractMachine.Machine;
+import Triangle.AbstractMachine.OpCode;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public class UnknownRoutine extends RuntimeEntity implements RoutineEntity {
+
+	private final ObjectAddress address;
+
+	public UnknownRoutine(int size, int level, int displacement) {
+		super(size);
+		address = new ObjectAddress(level, displacement);
+	}
+
+	public final ObjectAddress getAddress() {
+		return address;
+	}
+
+	public void encodeCall(Emitter emitter, Frame frame) {
+		emitter.emit(OpCode.LOAD, Machine.closureSize, frame.getDisplayRegister(address), address.getDisplacement());
+		emitter.emit(OpCode.CALLI, 0);
+	}
+
+	public void encodeFetch(Emitter emitter, Frame frame) {
+		emitter.emit(OpCode.LOAD, Machine.closureSize, frame.getDisplayRegister(address), address.getDisplacement());
+	}
+
+}
\ No newline at end of file
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/UnknownValue.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/UnknownValue.java
new file mode 100644
index 0000000..ba37c23
--- /dev/null
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Entities/UnknownValue.java
@@ -0,0 +1,51 @@
+/*
+ * @(#)UnknownValue.java                        2.1 2003/10/07
+ *
+ * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
+ * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
+ * and School of Computer and Math Sciences, The Robert Gordon University,
+ * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
+ * All rights reserved.
+ *
+ * This software is provided free for educational use only. It may
+ * not be used for commercial purposes without the prior written permission
+ * of the authors.
+ */
+
+package Triangle.CodeGenerator.Entities;
+
+import Triangle.AbstractMachine.OpCode;
+import Triangle.AbstractMachine.Primitive;
+import Triangle.AbstractMachine.Register;
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
+import Triangle.CodeGenerator.Emitter;
+import Triangle.CodeGenerator.Frame;
+
+public class UnknownValue extends RuntimeEntity implements FetchableEntity {
+
+	private final ObjectAddress address;
+
+	public UnknownValue(int size, int level, int displacement) {
+		super(size);
+		address = new ObjectAddress(level, displacement);
+	}
+
+	public UnknownValue(int size, Frame frame) {
+		this(size, frame.getLevel(), frame.getSize());
+	}
+
+	public final ObjectAddress getAddress() {
+		return address;
+	}
+
+	public void encodeFetch(Emitter emitter, Frame frame, int size, Vname vname) {
+		if (vname.indexed) {
+			emitter.emit(OpCode.LOADA, 0, frame.getDisplayRegister(address), address.getDisplacement() + vname.offset);
+			emitter.emit(OpCode.CALL, Register.PB, Primitive.ADD);
+			emitter.emit(OpCode.LOADI, size, 0);
+		} else {
+			emitter.emit(OpCode.LOAD, size, frame.getDisplayRegister(address),
+					address.getDisplacement() + vname.offset);
+		}
+	}
+}
\ No newline at end of file
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/EqualityRoutine.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/EqualityRoutine.java
deleted file mode 100644
index 564e3ab..0000000
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/EqualityRoutine.java
+++ /dev/null
@@ -1,30 +0,0 @@
-/*
- * @(#)EqualityRoutine.java                        2.1 2003/10/07
- *
- * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
- * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
- * and School of Computer and Math Sciences, The Robert Gordon University,
- * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
- * All rights reserved.
- *
- * This software is provided free for educational use only. It may
- * not be used for commercial purposes without the prior written permission
- * of the authors.
- */
-
-package Triangle.CodeGenerator;
-
-public class EqualityRoutine extends RuntimeEntity {
-
-	public EqualityRoutine() {
-		super();
-	}
-
-	public EqualityRoutine(int size, int displacement) {
-		super(size);
-		this.displacement = displacement;
-	}
-
-	public int displacement;
-
-}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Frame.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Frame.java
index 2d784d8..a05b44c 100644
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Frame.java
+++ b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/Frame.java
@@ -14,33 +14,60 @@
 
 package Triangle.CodeGenerator;
 
+import Triangle.AbstractMachine.Register;
+import Triangle.CodeGenerator.Entities.ObjectAddress;
+
 public class Frame {
 
-	public Frame() {
-		this.level = 0;
-		this.size = 0;
-	}
+	public static final Frame Initial = new Frame(0, 0);
 
-	public Frame(int level, Integer size) {
-		this.level = level;
-		this.size = size.intValue();
-	}
+	private final int level;
 
-	public Frame(int level, int size) {
+	private final int size;
+
+	private Frame(int level, int size) {
 		this.level = level;
 		this.size = size;
 	}
 
-	public Frame(Frame frame, int sizeIncrement) {
-		this.level = frame.level;
-		this.size = frame.size + sizeIncrement;
+	public final int getLevel() {
+		return level;
+	}
+
+	public final int getSize() {
+		return size;
 	}
 
-	public Frame(Frame frame, Integer sizeIncrement) {
-		this.level = frame.level;
-		this.size = frame.size + sizeIncrement.intValue();
+	public Frame expand(int increment) {
+		return new Frame(level, size + increment);
 	}
 
-	protected int level;
-	protected int size;
+	public Frame replace(int size) {
+		return new Frame(level, size);
+	}
+
+	public Frame push(int size) {
+		return new Frame(level + 1, size);
+	}
+
+	/**
+	 * Returns the display register appropriate for object code at the current
+	 * static level to access a data object at the static level of the given
+	 * address.
+	 * 
+	 * @param address the address of the data object
+	 * @return the display register required for static addressing
+	 */
+	public Register getDisplayRegister(ObjectAddress address) {
+		if (address.getLevel() == 0) {
+			return Register.SB;
+		}
+
+		if (level - address.getLevel() <= 6) {
+			return Register.values()[Register.LB.ordinal() + level - address.getLevel()]; // LB|L1|...|L6
+		}
+
+		// _errorReporter.ReportRestriction("can't access data more than 6 levels out");
+		return Register.L6; // to allow code generation to continue
+	}
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/KnownAddress.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/KnownAddress.java
deleted file mode 100644
index 3e84c59..0000000
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/KnownAddress.java
+++ /dev/null
@@ -1,31 +0,0 @@
-/*
- * @(#)KnownAddress.java                        2.1 2003/10/07
- *
- * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
- * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
- * and School of Computer and Math Sciences, The Robert Gordon University,
- * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
- * All rights reserved.
- *
- * This software is provided free for educational use only. It may
- * not be used for commercial purposes without the prior written permission
- * of the authors.
- */
-
-package Triangle.CodeGenerator;
-
-public class KnownAddress extends RuntimeEntity {
-
-	public KnownAddress() {
-		super();
-		address = null;
-	}
-
-	public KnownAddress(int size, int level, int displacement) {
-		super(size);
-		address = new ObjectAddress(level, displacement);
-	}
-
-	public ObjectAddress address;
-
-}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/KnownRoutine.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/KnownRoutine.java
deleted file mode 100644
index 4262c6b..0000000
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/KnownRoutine.java
+++ /dev/null
@@ -1,31 +0,0 @@
-/*
- * @(#)KnownRoutine.java                        2.1 2003/10/07
- *
- * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
- * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
- * and School of Computer and Math Sciences, The Robert Gordon University,
- * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
- * All rights reserved.
- *
- * This software is provided free for educational use only. It may
- * not be used for commercial purposes without the prior written permission
- * of the authors.
- */
-
-package Triangle.CodeGenerator;
-
-public class KnownRoutine extends RuntimeEntity {
-
-	public KnownRoutine() {
-		super();
-		address = null;
-	}
-
-	public KnownRoutine(int size, int level, int displacement) {
-		super(size);
-		address = new ObjectAddress(level, displacement);
-	}
-
-	public ObjectAddress address;
-
-}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/PrimitiveRoutine.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/PrimitiveRoutine.java
deleted file mode 100644
index e857dd5..0000000
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/PrimitiveRoutine.java
+++ /dev/null
@@ -1,31 +0,0 @@
-/*
- * @(#)PrimitiveRoutine.java                        2.1 2003/10/07
- *
- * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
- * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
- * and School of Computer and Math Sciences, The Robert Gordon University,
- * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
- * All rights reserved.
- *
- * This software is provided free for educational use only. It may
- * not be used for commercial purposes without the prior written permission
- * of the authors.
- */
-
-package Triangle.CodeGenerator;
-
-public class PrimitiveRoutine extends RuntimeEntity {
-
-	public PrimitiveRoutine() {
-		super();
-		displacement = 0;
-	}
-
-	public PrimitiveRoutine(int size, int displacement) {
-		super(size);
-		this.displacement = displacement;
-	}
-
-	public int displacement;
-
-}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/UnknownAddress.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/UnknownAddress.java
deleted file mode 100644
index d3ff717..0000000
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/UnknownAddress.java
+++ /dev/null
@@ -1,31 +0,0 @@
-/*
- * @(#)UnknownAddress.java                        2.1 2003/10/07
- *
- * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
- * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
- * and School of Computer and Math Sciences, The Robert Gordon University,
- * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
- * All rights reserved.
- *
- * This software is provided free for educational use only. It may
- * not be used for commercial purposes without the prior written permission
- * of the authors.
- */
-
-package Triangle.CodeGenerator;
-
-public class UnknownAddress extends RuntimeEntity {
-
-	public UnknownAddress() {
-		super();
-		address = null;
-	}
-
-	public UnknownAddress(int size, int level, int displacement) {
-		super(size);
-		address = new ObjectAddress(level, displacement);
-	}
-
-	public ObjectAddress address;
-
-}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/UnknownRoutine.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/UnknownRoutine.java
deleted file mode 100644
index 0b2d4ea..0000000
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/UnknownRoutine.java
+++ /dev/null
@@ -1,31 +0,0 @@
-/*
- * @(#)UnknownRoutine.java                        2.1 2003/10/07
- *
- * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
- * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
- * and School of Computer and Math Sciences, The Robert Gordon University,
- * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
- * All rights reserved.
- *
- * This software is provided free for educational use only. It may
- * not be used for commercial purposes without the prior written permission
- * of the authors.
- */
-
-package Triangle.CodeGenerator;
-
-public class UnknownRoutine extends RuntimeEntity {
-
-	public UnknownRoutine() {
-		super();
-		address = null;
-	}
-
-	public UnknownRoutine(int size, int level, int displacement) {
-		super(size);
-		address = new ObjectAddress(level, displacement);
-	}
-
-	public ObjectAddress address;
-
-}
diff --git a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/UnknownValue.java b/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/UnknownValue.java
deleted file mode 100644
index 3918607..0000000
--- a/Triangle.Compiler/src/main/java/Triangle/CodeGenerator/UnknownValue.java
+++ /dev/null
@@ -1,31 +0,0 @@
-/*
- * @(#)UnknownValue.java                        2.1 2003/10/07
- *
- * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
- * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
- * and School of Computer and Math Sciences, The Robert Gordon University,
- * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
- * All rights reserved.
- *
- * This software is provided free for educational use only. It may
- * not be used for commercial purposes without the prior written permission
- * of the authors.
- */
-
-package Triangle.CodeGenerator;
-
-public class UnknownValue extends RuntimeEntity {
-
-	public UnknownValue() {
-		super();
-		address = null;
-	}
-
-	public UnknownValue(int size, int level, int displacement) {
-		super(size);
-		address = new ObjectAddress(level, displacement);
-	}
-
-	public ObjectAddress address;
-
-}
diff --git a/Triangle.Compiler/src/main/java/Triangle/Compiler.java b/Triangle.Compiler/src/main/java/Triangle/Compiler.java
index 0fc04b1..0d68c42 100644
--- a/Triangle.Compiler/src/main/java/Triangle/Compiler.java
+++ b/Triangle.Compiler/src/main/java/Triangle/Compiler.java
@@ -15,6 +15,7 @@
 package Triangle;
 
 import Triangle.AbstractSyntaxTrees.Program;
+import Triangle.CodeGenerator.Emitter;
 import Triangle.CodeGenerator.Encoder;
 import Triangle.ContextualAnalyzer.Checker;
 import Triangle.SyntacticAnalyzer.Parser;
@@ -37,6 +38,7 @@ public class Compiler {
 	private static Parser parser;
 	private static Checker checker;
 	private static Encoder encoder;
+	private static Emitter emitter;
 	private static ErrorReporter reporter;
 	private static Drawer drawer;
 
@@ -72,7 +74,8 @@ public class Compiler {
 		reporter = new ErrorReporter();
 		parser = new Parser(scanner, reporter);
 		checker = new Checker(reporter);
-		encoder = new Encoder(reporter);
+		encoder = new Encoder(emitter, reporter);
+		emitter = new Emitter(reporter);
 		drawer = new Drawer();
 
 		// scanner.enableDebugging();
@@ -94,7 +97,7 @@ public class Compiler {
 
 		boolean successful = (reporter.numErrors == 0);
 		if (successful) {
-			encoder.saveObjectProgram(objectName);
+			emitter.saveObjectProgram(objectName);
 			System.out.println("Compilation was successful.");
 		} else {
 			System.out.println("Compilation was unsuccessful.");
diff --git a/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/Checker.java b/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/Checker.java
index 0b157b5..a97af88 100644
--- a/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/Checker.java
+++ b/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/Checker.java
@@ -16,126 +16,156 @@ package Triangle.ContextualAnalyzer;
 
 import Triangle.ErrorReporter;
 import Triangle.StdEnvironment;
-import Triangle.AbstractSyntaxTrees.AnyTypeDenoter;
-import Triangle.AbstractSyntaxTrees.ArrayExpression;
-import Triangle.AbstractSyntaxTrees.ArrayTypeDenoter;
-import Triangle.AbstractSyntaxTrees.AssignCommand;
-import Triangle.AbstractSyntaxTrees.BinaryExpression;
-import Triangle.AbstractSyntaxTrees.BinaryOperatorDeclaration;
-import Triangle.AbstractSyntaxTrees.BoolTypeDenoter;
-import Triangle.AbstractSyntaxTrees.CallCommand;
-import Triangle.AbstractSyntaxTrees.CallExpression;
-import Triangle.AbstractSyntaxTrees.CharTypeDenoter;
-import Triangle.AbstractSyntaxTrees.CharacterExpression;
-import Triangle.AbstractSyntaxTrees.CharacterLiteral;
-import Triangle.AbstractSyntaxTrees.ConstActualParameter;
-import Triangle.AbstractSyntaxTrees.ConstDeclaration;
-import Triangle.AbstractSyntaxTrees.ConstFormalParameter;
-import Triangle.AbstractSyntaxTrees.Declaration;
-import Triangle.AbstractSyntaxTrees.DotVname;
-import Triangle.AbstractSyntaxTrees.EmptyActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.EmptyCommand;
-import Triangle.AbstractSyntaxTrees.EmptyExpression;
-import Triangle.AbstractSyntaxTrees.EmptyFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.ErrorTypeDenoter;
-import Triangle.AbstractSyntaxTrees.FieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.FormalParameter;
-import Triangle.AbstractSyntaxTrees.FormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.FuncActualParameter;
-import Triangle.AbstractSyntaxTrees.FuncDeclaration;
-import Triangle.AbstractSyntaxTrees.FuncFormalParameter;
-import Triangle.AbstractSyntaxTrees.Identifier;
-import Triangle.AbstractSyntaxTrees.IfCommand;
-import Triangle.AbstractSyntaxTrees.IfExpression;
-import Triangle.AbstractSyntaxTrees.IntTypeDenoter;
-import Triangle.AbstractSyntaxTrees.IntegerExpression;
-import Triangle.AbstractSyntaxTrees.IntegerLiteral;
-import Triangle.AbstractSyntaxTrees.LetCommand;
-import Triangle.AbstractSyntaxTrees.LetExpression;
-import Triangle.AbstractSyntaxTrees.MultipleActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.MultipleArrayAggregate;
-import Triangle.AbstractSyntaxTrees.MultipleFieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.MultipleFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.MultipleRecordAggregate;
-import Triangle.AbstractSyntaxTrees.Operator;
-import Triangle.AbstractSyntaxTrees.ProcActualParameter;
-import Triangle.AbstractSyntaxTrees.ProcDeclaration;
-import Triangle.AbstractSyntaxTrees.ProcFormalParameter;
 import Triangle.AbstractSyntaxTrees.Program;
-import Triangle.AbstractSyntaxTrees.RecordExpression;
-import Triangle.AbstractSyntaxTrees.RecordTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SequentialCommand;
-import Triangle.AbstractSyntaxTrees.SequentialDeclaration;
-import Triangle.AbstractSyntaxTrees.SimpleTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SimpleVname;
-import Triangle.AbstractSyntaxTrees.SingleActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.SingleArrayAggregate;
-import Triangle.AbstractSyntaxTrees.SingleFieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SingleFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.SingleRecordAggregate;
-import Triangle.AbstractSyntaxTrees.SubscriptVname;
-import Triangle.AbstractSyntaxTrees.Terminal;
-import Triangle.AbstractSyntaxTrees.TypeDeclaration;
-import Triangle.AbstractSyntaxTrees.TypeDenoter;
-import Triangle.AbstractSyntaxTrees.UnaryExpression;
-import Triangle.AbstractSyntaxTrees.UnaryOperatorDeclaration;
-import Triangle.AbstractSyntaxTrees.VarActualParameter;
-import Triangle.AbstractSyntaxTrees.VarDeclaration;
-import Triangle.AbstractSyntaxTrees.VarFormalParameter;
-import Triangle.AbstractSyntaxTrees.Visitor;
-import Triangle.AbstractSyntaxTrees.VnameExpression;
-import Triangle.AbstractSyntaxTrees.WhileCommand;
+import Triangle.AbstractSyntaxTrees.Actuals.ConstActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.EmptyActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.FuncActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.MultipleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.ProcActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.SingleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.VarActualParameter;
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Commands.AssignCommand;
+import Triangle.AbstractSyntaxTrees.Commands.CallCommand;
+import Triangle.AbstractSyntaxTrees.Commands.EmptyCommand;
+import Triangle.AbstractSyntaxTrees.Commands.IfCommand;
+import Triangle.AbstractSyntaxTrees.Commands.LetCommand;
+import Triangle.AbstractSyntaxTrees.Commands.SequentialCommand;
+import Triangle.AbstractSyntaxTrees.Commands.WhileCommand;
+import Triangle.AbstractSyntaxTrees.Declarations.BinaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ConstDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
+import Triangle.AbstractSyntaxTrees.Declarations.FuncDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ProcDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.SequentialDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.UnaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.VarDeclaration;
+import Triangle.AbstractSyntaxTrees.Expressions.ArrayExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.BinaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CallExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CharacterExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.EmptyExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.IfExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.IntegerExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.LetExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.RecordExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.UnaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.VnameExpression;
+import Triangle.AbstractSyntaxTrees.Formals.ConstFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.EmptyFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.FormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.FormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.FuncFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.MultipleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.ProcFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.SingleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.VarFormalParameter;
+import Triangle.AbstractSyntaxTrees.Terminals.CharacterLiteral;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Terminals.IntegerLiteral;
+import Triangle.AbstractSyntaxTrees.Terminals.Operator;
+import Triangle.AbstractSyntaxTrees.Terminals.Terminal;
+import Triangle.AbstractSyntaxTrees.Types.AnyTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.ArrayTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.BoolTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.CharTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.ErrorTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.FieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.IntTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.MultipleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.RecordTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SimpleTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SingleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.TypeDeclaration;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterSequenceVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ArrayAggregateVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterSequenceVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.IdentifierVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.LiteralVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.OperatorVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ProgramVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.RecordAggregateVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.VnameVisitor;
+import Triangle.AbstractSyntaxTrees.Vnames.DotVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SimpleVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SubscriptVname;
 import Triangle.SyntacticAnalyzer.SourcePosition;
 
-public final class Checker implements Visitor {
+public final class Checker implements ActualParameterVisitor<FormalParameter, Void>,
+		ActualParameterSequenceVisitor<FormalParameterSequence, Void>, ArrayAggregateVisitor<Void, TypeDenoter>,
+		CommandVisitor<Void, Void>, DeclarationVisitor<Void, Void>, ExpressionVisitor<Void, TypeDenoter>,
+		FormalParameterVisitor<Void, Void>, FormalParameterSequenceVisitor<Void, Void>,
+		IdentifierVisitor<Void, Declaration>, LiteralVisitor<Void, TypeDenoter>, OperatorVisitor<Void, Declaration>,
+		ProgramVisitor<Void, Void>, RecordAggregateVisitor<Void, FieldTypeDenoter>,
+		TypeDenoterVisitor<Void, TypeDenoter>, VnameVisitor<Void, TypeDenoter> {
 
 	// Commands
 
 	// Always returns null. Does not use the given object.
 
 	@Override
-	public Object visitAssignCommand(AssignCommand ast, Object o) {
-		TypeDenoter vType = (TypeDenoter) ast.V.visit(this);
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
-		if (!ast.V.variable)
-			reporter.reportError("LHS of assignment is not a variable", "", ast.V.position);
-		if (!eType.equals(vType))
-			reporter.reportError("assignment incompatibilty", "", ast.position);
+	public Void visitAssignCommand(AssignCommand ast, Void arg) {
+		var vType = ast.V.visit(this);
+		var eType = ast.E.visit(this);
+
+		if (!ast.V.variable) {
+			reporter.reportError("LHS of assignment is not a variable", "", ast.V.getPosition());
+		}
+
+		if (!eType.equals(vType)) {
+			reporter.reportError("assignment incompatibilty", "", ast.getPosition());
+		}
+
 		return null;
 	}
 
 	@Override
-	public Object visitCallCommand(CallCommand ast, Object o) {
+	public Void visitCallCommand(CallCommand ast, Void arg) {
 
-		Declaration binding = (Declaration) ast.I.visit(this);
-		if (binding == null)
+		var binding = ast.I.visit(this);
+		if (binding == null) {
 			reportUndeclared(ast.I);
-		else if (binding instanceof ProcDeclaration) {
+		} else if (binding instanceof ProcDeclaration) {
 			ast.APS.visit(this, ((ProcDeclaration) binding).FPS);
 		} else if (binding instanceof ProcFormalParameter) {
 			ast.APS.visit(this, ((ProcFormalParameter) binding).FPS);
-		} else
-			reporter.reportError("\"%\" is not a procedure identifier", ast.I.spelling, ast.I.position);
+		} else {
+			reporter.reportError("\"%\" is not a procedure identifier", ast.I.spelling, ast.I.getPosition());
+		}
+
 		return null;
 	}
 
 	@Override
-	public Object visitEmptyCommand(EmptyCommand ast, Object o) {
+	public Void visitEmptyCommand(EmptyCommand ast, Void arg) {
 		return null;
 	}
 
 	@Override
-	public Object visitIfCommand(IfCommand ast, Object o) {
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
-		if (!eType.equals(StdEnvironment.booleanType))
-			reporter.reportError("Boolean expression expected here", "", ast.E.position);
+	public Void visitIfCommand(IfCommand ast, Void arg) {
+		var eType = ast.E.visit(this);
+		if (!eType.equals(StdEnvironment.booleanType)) {
+			reporter.reportError("Boolean expression expected here", "", ast.E.getPosition());
+		}
+
 		ast.C1.visit(this);
 		ast.C2.visit(this);
+
 		return null;
 	}
 
 	@Override
-	public Object visitLetCommand(LetCommand ast, Object o) {
+	public Void visitLetCommand(LetCommand ast, Void arg) {
 		idTable.openScope();
 		ast.D.visit(this);
 		ast.C.visit(this);
@@ -144,17 +174,18 @@ public final class Checker implements Visitor {
 	}
 
 	@Override
-	public Object visitSequentialCommand(SequentialCommand ast, Object o) {
+	public Void visitSequentialCommand(SequentialCommand ast, Void arg) {
 		ast.C1.visit(this);
 		ast.C2.visit(this);
 		return null;
 	}
 
 	@Override
-	public Object visitWhileCommand(WhileCommand ast, Object o) {
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
-		if (!eType.equals(StdEnvironment.booleanType))
-			reporter.reportError("Boolean expression expected here", "", ast.E.position);
+	public Void visitWhileCommand(WhileCommand ast, Void arg) {
+		var eType = ast.E.visit(this);
+		if (!eType.equals(StdEnvironment.booleanType)) {
+			reporter.reportError("Boolean expression expected here", "", ast.E.getPosition());
+		}
 		ast.C.visit(this);
 		return null;
 	}
@@ -165,42 +196,46 @@ public final class Checker implements Visitor {
 	// not use the given object.
 
 	@Override
-	public Object visitArrayExpression(ArrayExpression ast, Object o) {
-		TypeDenoter elemType = (TypeDenoter) ast.AA.visit(this);
-		IntegerLiteral il = new IntegerLiteral(Integer.valueOf(ast.AA.elemCount).toString(), ast.position);
-		ast.type = new ArrayTypeDenoter(il, elemType, ast.position);
+	public TypeDenoter visitArrayExpression(ArrayExpression ast, Void arg) {
+		var elemType = ast.AA.visit(this);
+		var il = new IntegerLiteral(Integer.toString(ast.AA.elemCount), ast.getPosition());
+		ast.type = new ArrayTypeDenoter(il, elemType, ast.getPosition());
 		return ast.type;
 	}
 
 	@Override
-	public Object visitBinaryExpression(BinaryExpression ast, Object o) {
+	public TypeDenoter visitBinaryExpression(BinaryExpression ast, Void arg) {
 
-		TypeDenoter e1Type = (TypeDenoter) ast.E1.visit(this);
-		TypeDenoter e2Type = (TypeDenoter) ast.E2.visit(this);
-		Declaration binding = (Declaration) ast.O.visit(this);
+		var e1Type = ast.E1.visit(this);
+		var e2Type = ast.E2.visit(this);
+		var binding = ast.O.visit(this);
 
-		if (binding == null)
+		if (binding == null) {
 			reportUndeclared(ast.O);
-		else {
+		} else {
 			if (!(binding instanceof BinaryOperatorDeclaration))
-				reporter.reportError("\"%\" is not a binary operator", ast.O.spelling, ast.O.position);
-			BinaryOperatorDeclaration bbinding = (BinaryOperatorDeclaration) binding;
+				reporter.reportError("\"%\" is not a binary operator", ast.O.spelling, ast.O.getPosition());
+			var bbinding = (BinaryOperatorDeclaration) binding;
 			if (bbinding.ARG1 == StdEnvironment.anyType) {
 				// this operator must be "=" or "\="
-				if (!e1Type.equals(e2Type))
-					reporter.reportError("incompatible argument types for \"%\"", ast.O.spelling, ast.position);
-			} else if (!e1Type.equals(bbinding.ARG1))
-				reporter.reportError("wrong argument type for \"%\"", ast.O.spelling, ast.E1.position);
-			else if (!e2Type.equals(bbinding.ARG2))
-				reporter.reportError("wrong argument type for \"%\"", ast.O.spelling, ast.E2.position);
+				if (!e1Type.equals(e2Type)) {
+					reporter.reportError("incompatible argument types for \"%\"", ast.O.spelling, ast.getPosition());
+				}
+			} else if (!e1Type.equals(bbinding.ARG1)) {
+				reporter.reportError("wrong argument type for \"%\"", ast.O.spelling, ast.E1.getPosition());
+			} else if (!e2Type.equals(bbinding.ARG2)) {
+				reporter.reportError("wrong argument type for \"%\"", ast.O.spelling, ast.E2.getPosition());
+			}
+
 			ast.type = bbinding.RES;
 		}
+
 		return ast.type;
 	}
 
 	@Override
-	public Object visitCallExpression(CallExpression ast, Object o) {
-		Declaration binding = (Declaration) ast.I.visit(this);
+	public TypeDenoter visitCallExpression(CallExpression ast, Void arg) {
+		var binding = ast.I.visit(this);
 		if (binding == null) {
 			reportUndeclared(ast.I);
 			ast.type = StdEnvironment.errorType;
@@ -210,80 +245,85 @@ public final class Checker implements Visitor {
 		} else if (binding instanceof FuncFormalParameter) {
 			ast.APS.visit(this, ((FuncFormalParameter) binding).FPS);
 			ast.type = ((FuncFormalParameter) binding).T;
-		} else
-			reporter.reportError("\"%\" is not a function identifier", ast.I.spelling, ast.I.position);
+		} else {
+			reporter.reportError("\"%\" is not a function identifier", ast.I.spelling, ast.I.getPosition());
+		}
+
 		return ast.type;
 	}
 
 	@Override
-	public Object visitCharacterExpression(CharacterExpression ast, Object o) {
+	public TypeDenoter visitCharacterExpression(CharacterExpression ast, Void arg) {
 		ast.type = StdEnvironment.charType;
 		return ast.type;
 	}
 
 	@Override
-	public Object visitEmptyExpression(EmptyExpression ast, Object o) {
+	public TypeDenoter visitEmptyExpression(EmptyExpression ast, Void arg) {
 		ast.type = null;
 		return ast.type;
 	}
 
 	@Override
-	public Object visitIfExpression(IfExpression ast, Object o) {
-		TypeDenoter e1Type = (TypeDenoter) ast.E1.visit(this);
-		if (!e1Type.equals(StdEnvironment.booleanType))
-			reporter.reportError("Boolean expression expected here", "", ast.E1.position);
-		TypeDenoter e2Type = (TypeDenoter) ast.E2.visit(this);
-		TypeDenoter e3Type = (TypeDenoter) ast.E3.visit(this);
-		if (!e2Type.equals(e3Type))
-			reporter.reportError("incompatible limbs in if-expression", "", ast.position);
+	public TypeDenoter visitIfExpression(IfExpression ast, Void arg) {
+		var e1Type = ast.E1.visit(this);
+		if (!e1Type.equals(StdEnvironment.booleanType)) {
+			reporter.reportError("Boolean expression expected here", "", ast.E1.getPosition());
+		}
+		var e2Type = ast.E2.visit(this);
+		var e3Type = ast.E3.visit(this);
+		if (!e2Type.equals(e3Type)) {
+			reporter.reportError("incompatible limbs in if-expression", "", ast.getPosition());
+		}
 		ast.type = e2Type;
 		return ast.type;
 	}
 
 	@Override
-	public Object visitIntegerExpression(IntegerExpression ast, Object o) {
+	public TypeDenoter visitIntegerExpression(IntegerExpression ast, Void arg) {
 		ast.type = StdEnvironment.integerType;
 		return ast.type;
 	}
 
 	@Override
-	public Object visitLetExpression(LetExpression ast, Object o) {
+	public TypeDenoter visitLetExpression(LetExpression ast, Void arg) {
 		idTable.openScope();
 		ast.D.visit(this);
-		ast.type = (TypeDenoter) ast.E.visit(this);
+		ast.type = ast.E.visit(this);
 		idTable.closeScope();
 		return ast.type;
 	}
 
 	@Override
-	public Object visitRecordExpression(RecordExpression ast, Object o) {
-		FieldTypeDenoter rType = (FieldTypeDenoter) ast.RA.visit(this);
-		ast.type = new RecordTypeDenoter(rType, ast.position);
+	public TypeDenoter visitRecordExpression(RecordExpression ast, Void arg) {
+		var rType = ast.RA.visit(this);
+		ast.type = new RecordTypeDenoter(rType, ast.getPosition());
 		return ast.type;
 	}
 
 	@Override
-	public Object visitUnaryExpression(UnaryExpression ast, Object o) {
+	public TypeDenoter visitUnaryExpression(UnaryExpression ast, Void arg) {
 
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
-		Declaration binding = (Declaration) ast.O.visit(this);
+		var eType = ast.E.visit(this);
+		var binding = ast.O.visit(this);
 		if (binding == null) {
 			reportUndeclared(ast.O);
 			ast.type = StdEnvironment.errorType;
-		} else if (!(binding instanceof UnaryOperatorDeclaration))
-			reporter.reportError("\"%\" is not a unary operator", ast.O.spelling, ast.O.position);
-		else {
-			UnaryOperatorDeclaration ubinding = (UnaryOperatorDeclaration) binding;
-			if (!eType.equals(ubinding.ARG))
-				reporter.reportError("wrong argument type for \"%\"", ast.O.spelling, ast.O.position);
+		} else if (!(binding instanceof UnaryOperatorDeclaration)) {
+			reporter.reportError("\"%\" is not a unary operator", ast.O.spelling, ast.O.getPosition());
+		} else {
+			var ubinding = (UnaryOperatorDeclaration) binding;
+			if (!eType.equals(ubinding.ARG)) {
+				reporter.reportError("wrong argument type for \"%\"", ast.O.spelling, ast.O.getPosition());
+			}
 			ast.type = ubinding.RES;
 		}
 		return ast.type;
 	}
 
 	@Override
-	public Object visitVnameExpression(VnameExpression ast, Object o) {
-		ast.type = (TypeDenoter) ast.V.visit(this);
+	public TypeDenoter visitVnameExpression(VnameExpression ast, Void arg) {
+		ast.type = ast.V.visit(this);
 		return ast.type;
 	}
 
@@ -291,39 +331,43 @@ public final class Checker implements Visitor {
 
 	// Always returns null. Does not use the given object.
 	@Override
-	public Object visitBinaryOperatorDeclaration(BinaryOperatorDeclaration ast, Object o) {
+	public Void visitBinaryOperatorDeclaration(BinaryOperatorDeclaration ast, Void arg) {
 		return null;
 	}
 
 	@Override
-	public Object visitConstDeclaration(ConstDeclaration ast, Object o) {
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
+	public Void visitConstDeclaration(ConstDeclaration ast, Void arg) {
+		ast.E.visit(this);
 		idTable.enter(ast.I.spelling, ast);
-		if (ast.duplicated)
-			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.position);
+		if (ast.duplicated) {
+			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitFuncDeclaration(FuncDeclaration ast, Object o) {
-		ast.T = (TypeDenoter) ast.T.visit(this);
+	public Void visitFuncDeclaration(FuncDeclaration ast, Void arg) {
+		ast.T = ast.T.visit(this);
 		idTable.enter(ast.I.spelling, ast); // permits recursion
-		if (ast.duplicated)
-			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.position);
+		if (ast.duplicated) {
+			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.getPosition());
+		}
 		idTable.openScope();
 		ast.FPS.visit(this);
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
+		var eType = ast.E.visit(this);
 		idTable.closeScope();
-		if (!ast.T.equals(eType))
-			reporter.reportError("body of function \"%\" has wrong type", ast.I.spelling, ast.E.position);
+		if (!ast.T.equals(eType)) {
+			reporter.reportError("body of function \"%\" has wrong type", ast.I.spelling, ast.E.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitProcDeclaration(ProcDeclaration ast, Object o) {
+	public Void visitProcDeclaration(ProcDeclaration ast, Void arg) {
 		idTable.enter(ast.I.spelling, ast); // permits recursion
-		if (ast.duplicated)
-			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.position);
+		if (ast.duplicated) {
+			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.getPosition());
+		}
 		idTable.openScope();
 		ast.FPS.visit(this);
 		ast.C.visit(this);
@@ -332,32 +376,34 @@ public final class Checker implements Visitor {
 	}
 
 	@Override
-	public Object visitSequentialDeclaration(SequentialDeclaration ast, Object o) {
+	public Void visitSequentialDeclaration(SequentialDeclaration ast, Void arg) {
 		ast.D1.visit(this);
 		ast.D2.visit(this);
 		return null;
 	}
 
 	@Override
-	public Object visitTypeDeclaration(TypeDeclaration ast, Object o) {
-		ast.T = (TypeDenoter) ast.T.visit(this);
+	public Void visitTypeDeclaration(TypeDeclaration ast, Void arg) {
+		ast.T = ast.T.visit(this);
 		idTable.enter(ast.I.spelling, ast);
-		if (ast.duplicated)
-			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.position);
+		if (ast.duplicated) {
+			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitUnaryOperatorDeclaration(UnaryOperatorDeclaration ast, Object o) {
+	public Void visitUnaryOperatorDeclaration(UnaryOperatorDeclaration ast, Void arg) {
 		return null;
 	}
 
 	@Override
-	public Object visitVarDeclaration(VarDeclaration ast, Object o) {
-		ast.T = (TypeDenoter) ast.T.visit(this);
+	public Void visitVarDeclaration(VarDeclaration ast, Void arg) {
+		ast.T = ast.T.visit(this);
 		idTable.enter(ast.I.spelling, ast);
-		if (ast.duplicated)
-			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.position);
+		if (ast.duplicated) {
+			reporter.reportError("identifier \"%\" already declared", ast.I.spelling, ast.getPosition());
+		}
 
 		return null;
 	}
@@ -368,18 +414,19 @@ public final class Checker implements Visitor {
 	// given object.
 
 	@Override
-	public Object visitMultipleArrayAggregate(MultipleArrayAggregate ast, Object o) {
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
-		TypeDenoter elemType = (TypeDenoter) ast.AA.visit(this);
+	public TypeDenoter visitMultipleArrayAggregate(MultipleArrayAggregate ast, Void arg) {
+		var eType = ast.E.visit(this);
+		var elemType = ast.AA.visit(this);
 		ast.elemCount = ast.AA.elemCount + 1;
-		if (!eType.equals(elemType))
-			reporter.reportError("incompatible array-aggregate element", "", ast.E.position);
+		if (!eType.equals(elemType)) {
+			reporter.reportError("incompatible array-aggregate element", "", ast.E.getPosition());
+		}
 		return elemType;
 	}
 
 	@Override
-	public Object visitSingleArrayAggregate(SingleArrayAggregate ast, Object o) {
-		TypeDenoter elemType = (TypeDenoter) ast.E.visit(this);
+	public TypeDenoter visitSingleArrayAggregate(SingleArrayAggregate ast, Void arg) {
+		var elemType = ast.E.visit(this);
 		ast.elemCount = 1;
 		return elemType;
 	}
@@ -390,20 +437,21 @@ public final class Checker implements Visitor {
 	// given object.
 
 	@Override
-	public Object visitMultipleRecordAggregate(MultipleRecordAggregate ast, Object o) {
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
-		FieldTypeDenoter rType = (FieldTypeDenoter) ast.RA.visit(this);
-		TypeDenoter fType = checkFieldIdentifier(rType, ast.I);
-		if (fType != StdEnvironment.errorType)
-			reporter.reportError("duplicate field \"%\" in record", ast.I.spelling, ast.I.position);
-		ast.type = new MultipleFieldTypeDenoter(ast.I, eType, rType, ast.position);
+	public FieldTypeDenoter visitMultipleRecordAggregate(MultipleRecordAggregate ast, Void arg) {
+		var eType = ast.E.visit(this);
+		var rType = ast.RA.visit(this);
+		var fType = checkFieldIdentifier(rType, ast.I);
+		if (fType != StdEnvironment.errorType) {
+			reporter.reportError("duplicate field \"%\" in record", ast.I.spelling, ast.I.getPosition());
+		}
+		ast.type = new MultipleFieldTypeDenoter(ast.I, eType, rType, ast.getPosition());
 		return ast.type;
 	}
 
 	@Override
-	public Object visitSingleRecordAggregate(SingleRecordAggregate ast, Object o) {
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
-		ast.type = new SingleFieldTypeDenoter(ast.I, eType, ast.position);
+	public FieldTypeDenoter visitSingleRecordAggregate(SingleRecordAggregate ast, Void arg) {
+		var eType = ast.E.visit(this);
+		ast.type = new SingleFieldTypeDenoter(ast.I, eType, ast.getPosition());
 		return ast.type;
 	}
 
@@ -412,60 +460,64 @@ public final class Checker implements Visitor {
 	// Always returns null. Does not use the given object.
 
 	@Override
-	public Object visitConstFormalParameter(ConstFormalParameter ast, Object o) {
-		ast.T = (TypeDenoter) ast.T.visit(this);
+	public Void visitConstFormalParameter(ConstFormalParameter ast, Void arg) {
+		ast.T = ast.T.visit(this);
 		idTable.enter(ast.I.spelling, ast);
-		if (ast.duplicated)
-			reporter.reportError("duplicated formal parameter \"%\"", ast.I.spelling, ast.position);
+		if (ast.duplicated) {
+			reporter.reportError("duplicated formal parameter \"%\"", ast.I.spelling, ast.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitFuncFormalParameter(FuncFormalParameter ast, Object o) {
+	public Void visitFuncFormalParameter(FuncFormalParameter ast, Void arg) {
 		idTable.openScope();
 		ast.FPS.visit(this);
 		idTable.closeScope();
-		ast.T = (TypeDenoter) ast.T.visit(this);
+		ast.T = ast.T.visit(this);
 		idTable.enter(ast.I.spelling, ast);
-		if (ast.duplicated)
-			reporter.reportError("duplicated formal parameter \"%\"", ast.I.spelling, ast.position);
+		if (ast.duplicated) {
+			reporter.reportError("duplicated formal parameter \"%\"", ast.I.spelling, ast.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitProcFormalParameter(ProcFormalParameter ast, Object o) {
+	public Void visitProcFormalParameter(ProcFormalParameter ast, Void arg) {
 		idTable.openScope();
 		ast.FPS.visit(this);
 		idTable.closeScope();
 		idTable.enter(ast.I.spelling, ast);
-		if (ast.duplicated)
-			reporter.reportError("duplicated formal parameter \"%\"", ast.I.spelling, ast.position);
+		if (ast.duplicated) {
+			reporter.reportError("duplicated formal parameter \"%\"", ast.I.spelling, ast.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitVarFormalParameter(VarFormalParameter ast, Object o) {
-		ast.T = (TypeDenoter) ast.T.visit(this);
+	public Void visitVarFormalParameter(VarFormalParameter ast, Void arg) {
+		ast.T = ast.T.visit(this);
 		idTable.enter(ast.I.spelling, ast);
-		if (ast.duplicated)
-			reporter.reportError("duplicated formal parameter \"%\"", ast.I.spelling, ast.position);
+		if (ast.duplicated) {
+			reporter.reportError("duplicated formal parameter \"%\"", ast.I.spelling, ast.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitEmptyFormalParameterSequence(EmptyFormalParameterSequence ast, Object o) {
+	public Void visitEmptyFormalParameterSequence(EmptyFormalParameterSequence ast, Void arg) {
 		return null;
 	}
 
 	@Override
-	public Object visitMultipleFormalParameterSequence(MultipleFormalParameterSequence ast, Object o) {
+	public Void visitMultipleFormalParameterSequence(MultipleFormalParameterSequence ast, Void arg) {
 		ast.FP.visit(this);
 		ast.FPS.visit(this);
 		return null;
 	}
 
 	@Override
-	public Object visitSingleFormalParameterSequence(SingleFormalParameterSequence ast, Object o) {
+	public Void visitSingleFormalParameterSequence(SingleFormalParameterSequence ast, Void arg) {
 		ast.FP.visit(this);
 		return null;
 	}
@@ -475,29 +527,26 @@ public final class Checker implements Visitor {
 	// Always returns null. Uses the given FormalParameter.
 
 	@Override
-	public Object visitConstActualParameter(ConstActualParameter ast, Object o) {
-		FormalParameter fp = (FormalParameter) o;
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
-
-		if (!(fp instanceof ConstFormalParameter))
-			reporter.reportError("const actual parameter not expected here", "", ast.position);
-		else if (!eType.equals(((ConstFormalParameter) fp).T))
-			reporter.reportError("wrong type for const actual parameter", "", ast.E.position);
+	public Void visitConstActualParameter(ConstActualParameter ast, FormalParameter arg) {
+		var eType = ast.E.visit(this);
+		if (!(arg instanceof ConstFormalParameter)) {
+			reporter.reportError("const actual parameter not expected here", "", ast.getPosition());
+		} else if (!eType.equals(((ConstFormalParameter) arg).T)) {
+			reporter.reportError("wrong type for const actual parameter", "", ast.E.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitFuncActualParameter(FuncActualParameter ast, Object o) {
-		FormalParameter fp = (FormalParameter) o;
-
-		Declaration binding = (Declaration) ast.I.visit(this);
-		if (binding == null)
+	public Void visitFuncActualParameter(FuncActualParameter ast, FormalParameter arg) {
+		var binding = ast.I.visit(this);
+		if (binding == null) {
 			reportUndeclared(ast.I);
-		else if (!(binding instanceof FuncDeclaration || binding instanceof FuncFormalParameter))
-			reporter.reportError("\"%\" is not a function identifier", ast.I.spelling, ast.I.position);
-		else if (!(fp instanceof FuncFormalParameter))
-			reporter.reportError("func actual parameter not expected here", "", ast.position);
-		else {
+		} else if (!(binding instanceof FuncDeclaration || binding instanceof FuncFormalParameter)) {
+			reporter.reportError("\"%\" is not a function identifier", ast.I.spelling, ast.I.getPosition());
+		} else if (!(arg instanceof FuncFormalParameter)) {
+			reporter.reportError("func actual parameter not expected here", "", ast.getPosition());
+		} else {
 			FormalParameterSequence FPS = null;
 			TypeDenoter T = null;
 			if (binding instanceof FuncDeclaration) {
@@ -507,78 +556,76 @@ public final class Checker implements Visitor {
 				FPS = ((FuncFormalParameter) binding).FPS;
 				T = ((FuncFormalParameter) binding).T;
 			}
-			if (!FPS.equals(((FuncFormalParameter) fp).FPS))
-				reporter.reportError("wrong signature for function \"%\"", ast.I.spelling, ast.I.position);
-			else if (!T.equals(((FuncFormalParameter) fp).T))
-				reporter.reportError("wrong type for function \"%\"", ast.I.spelling, ast.I.position);
+			if (!FPS.equals(((FuncFormalParameter) arg).FPS)) {
+				reporter.reportError("wrong signature for function \"%\"", ast.I.spelling, ast.I.getPosition());
+			} else if (!T.equals(((FuncFormalParameter) arg).T)) {
+				reporter.reportError("wrong type for function \"%\"", ast.I.spelling, ast.I.getPosition());
+			}
 		}
 		return null;
 	}
 
 	@Override
-	public Object visitProcActualParameter(ProcActualParameter ast, Object o) {
-		FormalParameter fp = (FormalParameter) o;
-
-		Declaration binding = (Declaration) ast.I.visit(this);
-		if (binding == null)
+	public Void visitProcActualParameter(ProcActualParameter ast, FormalParameter arg) {
+		var binding = ast.I.visit(this);
+		if (binding == null) {
 			reportUndeclared(ast.I);
-		else if (!(binding instanceof ProcDeclaration || binding instanceof ProcFormalParameter))
-			reporter.reportError("\"%\" is not a procedure identifier", ast.I.spelling, ast.I.position);
-		else if (!(fp instanceof ProcFormalParameter))
-			reporter.reportError("proc actual parameter not expected here", "", ast.position);
-		else {
+		} else if (!(binding instanceof ProcDeclaration || binding instanceof ProcFormalParameter)) {
+			reporter.reportError("\"%\" is not a procedure identifier", ast.I.spelling, ast.I.getPosition());
+		} else if (!(arg instanceof ProcFormalParameter)) {
+			reporter.reportError("proc actual parameter not expected here", "", ast.getPosition());
+		} else {
 			FormalParameterSequence FPS = null;
-			if (binding instanceof ProcDeclaration)
+			if (binding instanceof ProcDeclaration) {
 				FPS = ((ProcDeclaration) binding).FPS;
-			else
+			} else {
 				FPS = ((ProcFormalParameter) binding).FPS;
-			if (!FPS.equals(((ProcFormalParameter) fp).FPS))
-				reporter.reportError("wrong signature for procedure \"%\"", ast.I.spelling, ast.I.position);
+			}
+			if (!FPS.equals(((ProcFormalParameter) arg).FPS)) {
+				reporter.reportError("wrong signature for procedure \"%\"", ast.I.spelling, ast.I.getPosition());
+			}
 		}
 		return null;
 	}
 
 	@Override
-	public Object visitVarActualParameter(VarActualParameter ast, Object o) {
-		FormalParameter fp = (FormalParameter) o;
-
-		TypeDenoter vType = (TypeDenoter) ast.V.visit(this);
-		if (!ast.V.variable)
-			reporter.reportError("actual parameter is not a variable", "", ast.V.position);
-		else if (!(fp instanceof VarFormalParameter))
-			reporter.reportError("var actual parameter not expected here", "", ast.V.position);
-		else if (!vType.equals(((VarFormalParameter) fp).T))
-			reporter.reportError("wrong type for var actual parameter", "", ast.V.position);
+	public Void visitVarActualParameter(VarActualParameter ast, FormalParameter arg) {
+		var vType = ast.V.visit(this);
+		if (!ast.V.variable) {
+			reporter.reportError("actual parameter is not a variable", "", ast.V.getPosition());
+		} else if (!(arg instanceof VarFormalParameter)) {
+			reporter.reportError("var actual parameter not expected here", "", ast.V.getPosition());
+		} else if (!vType.equals(((VarFormalParameter) arg).T)) {
+			reporter.reportError("wrong type for var actual parameter", "", ast.V.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitEmptyActualParameterSequence(EmptyActualParameterSequence ast, Object o) {
-		FormalParameterSequence fps = (FormalParameterSequence) o;
-		if (!(fps instanceof EmptyFormalParameterSequence))
-			reporter.reportError("too few actual parameters", "", ast.position);
+	public Void visitEmptyActualParameterSequence(EmptyActualParameterSequence ast, FormalParameterSequence arg) {
+		if (!(arg instanceof EmptyFormalParameterSequence)) {
+			reporter.reportError("too few actual parameters", "", ast.getPosition());
+		}
 		return null;
 	}
 
 	@Override
-	public Object visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, Object o) {
-		FormalParameterSequence fps = (FormalParameterSequence) o;
-		if (!(fps instanceof MultipleFormalParameterSequence))
-			reporter.reportError("too many actual parameters", "", ast.position);
-		else {
-			ast.AP.visit(this, ((MultipleFormalParameterSequence) fps).FP);
-			ast.APS.visit(this, ((MultipleFormalParameterSequence) fps).FPS);
+	public Void visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, FormalParameterSequence arg) {
+		if (!(arg instanceof MultipleFormalParameterSequence)) {
+			reporter.reportError("too many actual parameters", "", ast.getPosition());
+		} else {
+			ast.AP.visit(this, ((MultipleFormalParameterSequence) arg).FP);
+			ast.APS.visit(this, ((MultipleFormalParameterSequence) arg).FPS);
 		}
 		return null;
 	}
 
 	@Override
-	public Object visitSingleActualParameterSequence(SingleActualParameterSequence ast, Object o) {
-		FormalParameterSequence fps = (FormalParameterSequence) o;
-		if (!(fps instanceof SingleFormalParameterSequence))
-			reporter.reportError("incorrect number of actual parameters", "", ast.position);
-		else {
-			ast.AP.visit(this, ((SingleFormalParameterSequence) fps).FP);
+	public Void visitSingleActualParameterSequence(SingleActualParameterSequence ast, FormalParameterSequence arg) {
+		if (!(arg instanceof SingleFormalParameterSequence)) {
+			reporter.reportError("incorrect number of actual parameters", "", ast.getPosition());
+		} else {
+			ast.AP.visit(this, ((SingleFormalParameterSequence) arg).FP);
 		}
 		return null;
 	}
@@ -589,94 +636,97 @@ public final class Checker implements Visitor {
 	// use the given object.
 
 	@Override
-	public Object visitAnyTypeDenoter(AnyTypeDenoter ast, Object o) {
+	public TypeDenoter visitAnyTypeDenoter(AnyTypeDenoter ast, Void arg) {
 		return StdEnvironment.anyType;
 	}
 
 	@Override
-	public Object visitArrayTypeDenoter(ArrayTypeDenoter ast, Object o) {
-		ast.T = (TypeDenoter) ast.T.visit(this);
-		if ((Integer.valueOf(ast.IL.spelling).intValue()) == 0)
-			reporter.reportError("arrays must not be empty", "", ast.IL.position);
+	public TypeDenoter visitArrayTypeDenoter(ArrayTypeDenoter ast, Void arg) {
+		ast.T = ast.T.visit(this);
+		if ((Integer.valueOf(ast.IL.spelling)) == 0) {
+			reporter.reportError("arrays must not be empty", "", ast.IL.getPosition());
+		}
 		return ast;
 	}
 
 	@Override
-	public Object visitBoolTypeDenoter(BoolTypeDenoter ast, Object o) {
+	public TypeDenoter visitBoolTypeDenoter(BoolTypeDenoter ast, Void arg) {
 		return StdEnvironment.booleanType;
 	}
 
 	@Override
-	public Object visitCharTypeDenoter(CharTypeDenoter ast, Object o) {
+	public TypeDenoter visitCharTypeDenoter(CharTypeDenoter ast, Void arg) {
 		return StdEnvironment.charType;
 	}
 
 	@Override
-	public Object visitErrorTypeDenoter(ErrorTypeDenoter ast, Object o) {
+	public TypeDenoter visitErrorTypeDenoter(ErrorTypeDenoter ast, Void arg) {
 		return StdEnvironment.errorType;
 	}
 
 	@Override
-	public Object visitSimpleTypeDenoter(SimpleTypeDenoter ast, Object o) {
-		Declaration binding = (Declaration) ast.I.visit(this);
+	public TypeDenoter visitSimpleTypeDenoter(SimpleTypeDenoter ast, Void arg) {
+		var binding = ast.I.visit(this);
 		if (binding == null) {
 			reportUndeclared(ast.I);
 			return StdEnvironment.errorType;
 		} else if (!(binding instanceof TypeDeclaration)) {
-			reporter.reportError("\"%\" is not a type identifier", ast.I.spelling, ast.I.position);
+			reporter.reportError("\"%\" is not a type identifier", ast.I.spelling, ast.I.getPosition());
 			return StdEnvironment.errorType;
 		}
 		return ((TypeDeclaration) binding).T;
 	}
 
 	@Override
-	public Object visitIntTypeDenoter(IntTypeDenoter ast, Object o) {
+	public TypeDenoter visitIntTypeDenoter(IntTypeDenoter ast, Void arg) {
 		return StdEnvironment.integerType;
 	}
 
 	@Override
-	public Object visitRecordTypeDenoter(RecordTypeDenoter ast, Object o) {
+	public TypeDenoter visitRecordTypeDenoter(RecordTypeDenoter ast, Void arg) {
 		ast.FT = (FieldTypeDenoter) ast.FT.visit(this);
 		return ast;
 	}
 
 	@Override
-	public Object visitMultipleFieldTypeDenoter(MultipleFieldTypeDenoter ast, Object o) {
-		ast.T = (TypeDenoter) ast.T.visit(this);
+	public TypeDenoter visitMultipleFieldTypeDenoter(MultipleFieldTypeDenoter ast, Void arg) {
+		ast.T = ast.T.visit(this);
 		ast.FT.visit(this);
 		return ast;
 	}
 
 	@Override
-	public Object visitSingleFieldTypeDenoter(SingleFieldTypeDenoter ast, Object o) {
-		ast.T = (TypeDenoter) ast.T.visit(this);
+	public TypeDenoter visitSingleFieldTypeDenoter(SingleFieldTypeDenoter ast, Void arg) {
+		ast.T = ast.T.visit(this);
 		return ast;
 	}
 
 	// Literals, Identifiers and Operators
 	@Override
-	public Object visitCharacterLiteral(CharacterLiteral CL, Object o) {
+	public TypeDenoter visitCharacterLiteral(CharacterLiteral CL, Void arg) {
 		return StdEnvironment.charType;
 	}
 
 	@Override
-	public Object visitIdentifier(Identifier I, Object o) {
-		Declaration binding = idTable.retrieve(I.spelling);
-		if (binding != null)
+	public Declaration visitIdentifier(Identifier I, Void arg) {
+		var binding = idTable.retrieve(I.spelling);
+		if (binding != null) {
 			I.decl = binding;
+		}
 		return binding;
 	}
 
 	@Override
-	public Object visitIntegerLiteral(IntegerLiteral IL, Object o) {
+	public TypeDenoter visitIntegerLiteral(IntegerLiteral IL, Void arg) {
 		return StdEnvironment.integerType;
 	}
 
 	@Override
-	public Object visitOperator(Operator O, Object o) {
-		Declaration binding = idTable.retrieve(O.spelling);
-		if (binding != null)
+	public Declaration visitOperator(Operator O, Void arg) {
+		var binding = idTable.retrieve(O.spelling);
+		if (binding != null) {
 			O.decl = binding;
+		}
 		return binding;
 	}
 
@@ -702,28 +752,29 @@ public final class Checker implements Visitor {
 	// given object.
 
 	@Override
-	public Object visitDotVname(DotVname ast, Object o) {
+	public TypeDenoter visitDotVname(DotVname ast, Void arg) {
 		ast.type = null;
-		TypeDenoter vType = (TypeDenoter) ast.V.visit(this);
+		var vType = ast.V.visit(this);
 		ast.variable = ast.V.variable;
-		if (!(vType instanceof RecordTypeDenoter))
-			reporter.reportError("record expected here", "", ast.V.position);
-		else {
+		if (!(vType instanceof RecordTypeDenoter)) {
+			reporter.reportError("record expected here", "", ast.V.getPosition());
+		} else {
 			ast.type = checkFieldIdentifier(((RecordTypeDenoter) vType).FT, ast.I);
-			if (ast.type == StdEnvironment.errorType)
-				reporter.reportError("no field \"%\" in this record type", ast.I.spelling, ast.I.position);
+			if (ast.type == StdEnvironment.errorType) {
+				reporter.reportError("no field \"%\" in this record type", ast.I.spelling, ast.I.getPosition());
+			}
 		}
 		return ast.type;
 	}
 
 	@Override
-	public Object visitSimpleVname(SimpleVname ast, Object o) {
+	public TypeDenoter visitSimpleVname(SimpleVname ast, Void arg) {
 		ast.variable = false;
 		ast.type = StdEnvironment.errorType;
-		Declaration binding = (Declaration) ast.I.visit(this);
-		if (binding == null)
+		var binding = ast.I.visit(this);
+		if (binding == null) {
 			reportUndeclared(ast.I);
-		else if (binding instanceof ConstDeclaration) {
+		} else if (binding instanceof ConstDeclaration) {
 			ast.type = ((ConstDeclaration) binding).E.type;
 			ast.variable = false;
 		} else if (binding instanceof VarDeclaration) {
@@ -735,22 +786,24 @@ public final class Checker implements Visitor {
 		} else if (binding instanceof VarFormalParameter) {
 			ast.type = ((VarFormalParameter) binding).T;
 			ast.variable = true;
-		} else
-			reporter.reportError("\"%\" is not a const or var identifier", ast.I.spelling, ast.I.position);
+		} else {
+			reporter.reportError("\"%\" is not a const or var identifier", ast.I.spelling, ast.I.getPosition());
+		}
 		return ast.type;
 	}
 
 	@Override
-	public Object visitSubscriptVname(SubscriptVname ast, Object o) {
-		TypeDenoter vType = (TypeDenoter) ast.V.visit(this);
+	public TypeDenoter visitSubscriptVname(SubscriptVname ast, Void arg) {
+		var vType = ast.V.visit(this);
 		ast.variable = ast.V.variable;
-		TypeDenoter eType = (TypeDenoter) ast.E.visit(this);
+		var eType = ast.E.visit(this);
 		if (vType != StdEnvironment.errorType) {
-			if (!(vType instanceof ArrayTypeDenoter))
-				reporter.reportError("array expected here", "", ast.V.position);
-			else {
-				if (!eType.equals(StdEnvironment.integerType))
-					reporter.reportError("Integer expression expected here", "", ast.E.position);
+			if (!(vType instanceof ArrayTypeDenoter)) {
+				reporter.reportError("array expected here", "", ast.V.getPosition());
+			} else {
+				if (!eType.equals(StdEnvironment.integerType)) {
+					reporter.reportError("Integer expression expected here", "", ast.E.getPosition());
+				}
 				ast.type = ((ArrayTypeDenoter) vType).T;
 			}
 		}
@@ -760,7 +813,7 @@ public final class Checker implements Visitor {
 	// Programs
 
 	@Override
-	public Object visitProgram(Program ast, Object o) {
+	public Void visitProgram(Program ast, Void arg) {
 		ast.C.visit(this);
 		return null;
 	}
@@ -794,12 +847,12 @@ public final class Checker implements Visitor {
 	// has not been declared.
 
 	private void reportUndeclared(Terminal leaf) {
-		reporter.reportError("\"%\" is not declared", leaf.spelling, leaf.position);
+		reporter.reportError("\"%\" is not declared", leaf.spelling, leaf.getPosition());
 	}
 
 	private static TypeDenoter checkFieldIdentifier(FieldTypeDenoter ast, Identifier I) {
 		if (ast instanceof MultipleFieldTypeDenoter) {
-			MultipleFieldTypeDenoter ft = (MultipleFieldTypeDenoter) ast;
+			var ft = (MultipleFieldTypeDenoter) ast;
 			if (ft.I.spelling.compareTo(I.spelling) == 0) {
 				I.decl = ast;
 				return ft.T;
@@ -807,7 +860,7 @@ public final class Checker implements Visitor {
 				return checkFieldIdentifier(ft.FT, I);
 			}
 		} else if (ast instanceof SingleFieldTypeDenoter) {
-			SingleFieldTypeDenoter ft = (SingleFieldTypeDenoter) ast;
+			var ft = (SingleFieldTypeDenoter) ast;
 			if (ft.I.spelling.compareTo(I.spelling) == 0) {
 				I.decl = ast;
 				return ft.T;
@@ -821,9 +874,7 @@ public final class Checker implements Visitor {
 
 	private TypeDeclaration declareStdType(String id, TypeDenoter typedenoter) {
 
-		TypeDeclaration binding;
-
-		binding = new TypeDeclaration(new Identifier(id, dummyPos), typedenoter, dummyPos);
+		var binding = new TypeDeclaration(new Identifier(id, dummyPos), typedenoter, dummyPos);
 		idTable.enter(id, binding);
 		return binding;
 	}
@@ -833,13 +884,10 @@ public final class Checker implements Visitor {
 
 	private ConstDeclaration declareStdConst(String id, TypeDenoter constType) {
 
-		IntegerExpression constExpr;
-		ConstDeclaration binding;
-
 		// constExpr used only as a placeholder for constType
-		constExpr = new IntegerExpression(null, dummyPos);
+		var constExpr = new IntegerExpression(null, dummyPos);
 		constExpr.type = constType;
-		binding = new ConstDeclaration(new Identifier(id, dummyPos), constExpr, dummyPos);
+		var binding = new ConstDeclaration(new Identifier(id, dummyPos), constExpr, dummyPos);
 		idTable.enter(id, binding);
 		return binding;
 	}
@@ -849,9 +897,7 @@ public final class Checker implements Visitor {
 
 	private ProcDeclaration declareStdProc(String id, FormalParameterSequence fps) {
 
-		ProcDeclaration binding;
-
-		binding = new ProcDeclaration(new Identifier(id, dummyPos), fps, new EmptyCommand(dummyPos), dummyPos);
+		var binding = new ProcDeclaration(new Identifier(id, dummyPos), fps, new EmptyCommand(dummyPos), dummyPos);
 		idTable.enter(id, binding);
 		return binding;
 	}
@@ -861,9 +907,7 @@ public final class Checker implements Visitor {
 
 	private FuncDeclaration declareStdFunc(String id, FormalParameterSequence fps, TypeDenoter resultType) {
 
-		FuncDeclaration binding;
-
-		binding = new FuncDeclaration(new Identifier(id, dummyPos), fps, resultType, new EmptyExpression(dummyPos),
+		var binding = new FuncDeclaration(new Identifier(id, dummyPos), fps, resultType, new EmptyExpression(dummyPos),
 				dummyPos);
 		idTable.enter(id, binding);
 		return binding;
@@ -875,9 +919,7 @@ public final class Checker implements Visitor {
 
 	private UnaryOperatorDeclaration declareStdUnaryOp(String op, TypeDenoter argType, TypeDenoter resultType) {
 
-		UnaryOperatorDeclaration binding;
-
-		binding = new UnaryOperatorDeclaration(new Operator(op, dummyPos), argType, resultType, dummyPos);
+		var binding = new UnaryOperatorDeclaration(new Operator(op, dummyPos), argType, resultType, dummyPos);
 		idTable.enter(op, binding);
 		return binding;
 	}
@@ -889,9 +931,8 @@ public final class Checker implements Visitor {
 	private BinaryOperatorDeclaration declareStdBinaryOp(String op, TypeDenoter arg1Type, TypeDenoter arg2type,
 			TypeDenoter resultType) {
 
-		BinaryOperatorDeclaration binding;
-
-		binding = new BinaryOperatorDeclaration(new Operator(op, dummyPos), arg1Type, arg2type, resultType, dummyPos);
+		var binding = new BinaryOperatorDeclaration(new Operator(op, dummyPos), arg1Type, arg2type, resultType,
+				dummyPos);
 		idTable.enter(op, binding);
 		return binding;
 	}
diff --git a/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/IdEntry.java b/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/IdEntry.java
index fc71b09..e9400f8 100644
--- a/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/IdEntry.java
+++ b/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/IdEntry.java
@@ -14,7 +14,7 @@
 
 package Triangle.ContextualAnalyzer;
 
-import Triangle.AbstractSyntaxTrees.Declaration;
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
 
 public class IdEntry {
 
diff --git a/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/IdentificationTable.java b/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/IdentificationTable.java
index 52853e7..28e8ed9 100644
--- a/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/IdentificationTable.java
+++ b/Triangle.Compiler/src/main/java/Triangle/ContextualAnalyzer/IdentificationTable.java
@@ -14,7 +14,7 @@
 
 package Triangle.ContextualAnalyzer;
 
-import Triangle.AbstractSyntaxTrees.Declaration;
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
 
 public final class IdentificationTable {
 
@@ -30,7 +30,6 @@ public final class IdentificationTable {
 	// current topmost level.
 
 	public void openScope() {
-
 		level++;
 	}
 
@@ -38,15 +37,12 @@ public final class IdentificationTable {
 	// all entries belonging to that level.
 
 	public void closeScope() {
-
-		IdEntry entry, local;
-
 		// Presumably, idTable.level > 0.
-		entry = this.latest;
+		var entry = this.latest;
 		while (entry.level == this.level) {
-			local = entry;
-			entry = local.previous;
+			entry = entry.previous;
 		}
+
 		this.level--;
 		this.latest = entry;
 	}
@@ -57,25 +53,8 @@ public final class IdentificationTable {
 	// same identifier at the current level.
 
 	public void enter(String id, Declaration attr) {
-
-		IdEntry entry = this.latest;
-		boolean present = false, searching = true;
-
-		// Check for duplicate entry ...
-		while (searching) {
-			if (entry == null || entry.level < this.level)
-				searching = false;
-			else if (entry.id.equals(id)) {
-				present = true;
-				searching = false;
-			} else
-				entry = entry.previous;
-		}
-
-		attr.duplicated = present;
-		// Add new entry ...
-		entry = new IdEntry(id, attr, this.level, this.latest);
-		this.latest = entry;
+		attr.duplicated = retrieve(id) != null;
+		this.latest = new IdEntry(id, attr, this.level, this.latest);
 	}
 
 	// Finds an entry for the given identifier in the identification table,
@@ -85,24 +64,18 @@ public final class IdentificationTable {
 	// otherwise returns the attribute field of the entry found.
 
 	public Declaration retrieve(String id) {
-
-		IdEntry entry;
-		Declaration attr = null;
-		boolean present = false, searching = true;
-
-		entry = this.latest;
-		while (searching) {
-			if (entry == null)
-				searching = false;
-			else if (entry.id.equals(id)) {
-				present = true;
-				searching = false;
-				attr = entry.attr;
-			} else
+		var entry = this.latest;
+		while (true) {
+			if (entry == null) {
+				break;
+			} else if (entry.id.equals(id)) {
+				return entry.attr;
+			} else {
 				entry = entry.previous;
+			}
 		}
 
-		return attr;
+		return null;
 	}
 
 }
diff --git a/Triangle.Compiler/src/main/java/Triangle/StdEnvironment.java b/Triangle.Compiler/src/main/java/Triangle/StdEnvironment.java
index c2e4182..b4e009b 100644
--- a/Triangle.Compiler/src/main/java/Triangle/StdEnvironment.java
+++ b/Triangle.Compiler/src/main/java/Triangle/StdEnvironment.java
@@ -14,13 +14,13 @@
 
 package Triangle;
 
-import Triangle.AbstractSyntaxTrees.BinaryOperatorDeclaration;
-import Triangle.AbstractSyntaxTrees.ConstDeclaration;
-import Triangle.AbstractSyntaxTrees.FuncDeclaration;
-import Triangle.AbstractSyntaxTrees.ProcDeclaration;
-import Triangle.AbstractSyntaxTrees.TypeDeclaration;
-import Triangle.AbstractSyntaxTrees.TypeDenoter;
-import Triangle.AbstractSyntaxTrees.UnaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.BinaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ConstDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.FuncDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ProcDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.UnaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Types.TypeDeclaration;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
 
 public final class StdEnvironment {
 
diff --git a/Triangle.Compiler/src/main/java/Triangle/SyntacticAnalyzer/Parser.java b/Triangle.Compiler/src/main/java/Triangle/SyntacticAnalyzer/Parser.java
index ba82d1c..ec57077 100644
--- a/Triangle.Compiler/src/main/java/Triangle/SyntacticAnalyzer/Parser.java
+++ b/Triangle.Compiler/src/main/java/Triangle/SyntacticAnalyzer/Parser.java
@@ -15,72 +15,72 @@
 package Triangle.SyntacticAnalyzer;
 
 import Triangle.ErrorReporter;
-import Triangle.AbstractSyntaxTrees.ActualParameter;
-import Triangle.AbstractSyntaxTrees.ActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.ArrayAggregate;
-import Triangle.AbstractSyntaxTrees.ArrayExpression;
-import Triangle.AbstractSyntaxTrees.ArrayTypeDenoter;
-import Triangle.AbstractSyntaxTrees.AssignCommand;
-import Triangle.AbstractSyntaxTrees.BinaryExpression;
-import Triangle.AbstractSyntaxTrees.CallCommand;
-import Triangle.AbstractSyntaxTrees.CallExpression;
-import Triangle.AbstractSyntaxTrees.CharacterExpression;
-import Triangle.AbstractSyntaxTrees.CharacterLiteral;
-import Triangle.AbstractSyntaxTrees.Command;
-import Triangle.AbstractSyntaxTrees.ConstActualParameter;
-import Triangle.AbstractSyntaxTrees.ConstDeclaration;
-import Triangle.AbstractSyntaxTrees.ConstFormalParameter;
-import Triangle.AbstractSyntaxTrees.Declaration;
-import Triangle.AbstractSyntaxTrees.DotVname;
-import Triangle.AbstractSyntaxTrees.EmptyActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.EmptyCommand;
-import Triangle.AbstractSyntaxTrees.EmptyFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.Expression;
-import Triangle.AbstractSyntaxTrees.FieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.FormalParameter;
-import Triangle.AbstractSyntaxTrees.FormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.FuncActualParameter;
-import Triangle.AbstractSyntaxTrees.FuncDeclaration;
-import Triangle.AbstractSyntaxTrees.FuncFormalParameter;
-import Triangle.AbstractSyntaxTrees.Identifier;
-import Triangle.AbstractSyntaxTrees.IfCommand;
-import Triangle.AbstractSyntaxTrees.IfExpression;
-import Triangle.AbstractSyntaxTrees.IntegerExpression;
-import Triangle.AbstractSyntaxTrees.IntegerLiteral;
-import Triangle.AbstractSyntaxTrees.LetCommand;
-import Triangle.AbstractSyntaxTrees.LetExpression;
-import Triangle.AbstractSyntaxTrees.MultipleActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.MultipleArrayAggregate;
-import Triangle.AbstractSyntaxTrees.MultipleFieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.MultipleFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.MultipleRecordAggregate;
-import Triangle.AbstractSyntaxTrees.Operator;
-import Triangle.AbstractSyntaxTrees.ProcActualParameter;
-import Triangle.AbstractSyntaxTrees.ProcDeclaration;
-import Triangle.AbstractSyntaxTrees.ProcFormalParameter;
 import Triangle.AbstractSyntaxTrees.Program;
-import Triangle.AbstractSyntaxTrees.RecordAggregate;
-import Triangle.AbstractSyntaxTrees.RecordExpression;
-import Triangle.AbstractSyntaxTrees.RecordTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SequentialCommand;
-import Triangle.AbstractSyntaxTrees.SequentialDeclaration;
-import Triangle.AbstractSyntaxTrees.SimpleTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SimpleVname;
-import Triangle.AbstractSyntaxTrees.SingleActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.SingleArrayAggregate;
-import Triangle.AbstractSyntaxTrees.SingleFieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SingleFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.SingleRecordAggregate;
-import Triangle.AbstractSyntaxTrees.SubscriptVname;
-import Triangle.AbstractSyntaxTrees.TypeDeclaration;
-import Triangle.AbstractSyntaxTrees.TypeDenoter;
-import Triangle.AbstractSyntaxTrees.UnaryExpression;
-import Triangle.AbstractSyntaxTrees.VarActualParameter;
-import Triangle.AbstractSyntaxTrees.VarDeclaration;
-import Triangle.AbstractSyntaxTrees.VarFormalParameter;
-import Triangle.AbstractSyntaxTrees.Vname;
-import Triangle.AbstractSyntaxTrees.VnameExpression;
-import Triangle.AbstractSyntaxTrees.WhileCommand;
+import Triangle.AbstractSyntaxTrees.Actuals.ActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.ActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.ConstActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.EmptyActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.FuncActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.MultipleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.ProcActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.SingleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.VarActualParameter;
+import Triangle.AbstractSyntaxTrees.Aggregates.ArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.RecordAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Commands.AssignCommand;
+import Triangle.AbstractSyntaxTrees.Commands.CallCommand;
+import Triangle.AbstractSyntaxTrees.Commands.Command;
+import Triangle.AbstractSyntaxTrees.Commands.EmptyCommand;
+import Triangle.AbstractSyntaxTrees.Commands.IfCommand;
+import Triangle.AbstractSyntaxTrees.Commands.LetCommand;
+import Triangle.AbstractSyntaxTrees.Commands.SequentialCommand;
+import Triangle.AbstractSyntaxTrees.Commands.WhileCommand;
+import Triangle.AbstractSyntaxTrees.Declarations.ConstDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.Declaration;
+import Triangle.AbstractSyntaxTrees.Declarations.FuncDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ProcDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.SequentialDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.VarDeclaration;
+import Triangle.AbstractSyntaxTrees.Expressions.ArrayExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.BinaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CallExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CharacterExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.Expression;
+import Triangle.AbstractSyntaxTrees.Expressions.IfExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.IntegerExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.LetExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.RecordExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.UnaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.VnameExpression;
+import Triangle.AbstractSyntaxTrees.Formals.ConstFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.EmptyFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.FormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.FormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.FuncFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.MultipleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.ProcFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.SingleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.VarFormalParameter;
+import Triangle.AbstractSyntaxTrees.Terminals.CharacterLiteral;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Terminals.IntegerLiteral;
+import Triangle.AbstractSyntaxTrees.Terminals.Operator;
+import Triangle.AbstractSyntaxTrees.Types.ArrayTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.FieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.MultipleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.RecordTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SimpleTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SingleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.TypeDeclaration;
+import Triangle.AbstractSyntaxTrees.Types.TypeDenoter;
+import Triangle.AbstractSyntaxTrees.Vnames.DotVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SimpleVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SubscriptVname;
+import Triangle.AbstractSyntaxTrees.Vnames.Vname;
 
 public class Parser {
 
@@ -543,7 +543,7 @@ public class Parser {
 
 	Vname parseRestOfVname(Identifier identifierAST) throws SyntaxError {
 		SourcePosition vnamePos = new SourcePosition();
-		vnamePos = identifierAST.position;
+		vnamePos = identifierAST.getPosition();
 		Vname vAST = new SimpleVname(identifierAST, vnamePos);
 
 		while (currentToken.kind == Token.DOT || currentToken.kind == Token.LBRACKET) {
diff --git a/Triangle.Compiler/src/main/java/Triangle/TreeDrawer/LayoutVisitor.java b/Triangle.Compiler/src/main/java/Triangle/TreeDrawer/LayoutVisitor.java
index 158733a..4f7487e 100644
--- a/Triangle.Compiler/src/main/java/Triangle/TreeDrawer/LayoutVisitor.java
+++ b/Triangle.Compiler/src/main/java/Triangle/TreeDrawer/LayoutVisitor.java
@@ -16,72 +16,91 @@ package Triangle.TreeDrawer;
 
 import java.awt.FontMetrics;
 
-import Triangle.AbstractSyntaxTrees.AST;
-import Triangle.AbstractSyntaxTrees.AnyTypeDenoter;
-import Triangle.AbstractSyntaxTrees.ArrayExpression;
-import Triangle.AbstractSyntaxTrees.ArrayTypeDenoter;
-import Triangle.AbstractSyntaxTrees.AssignCommand;
-import Triangle.AbstractSyntaxTrees.BinaryExpression;
-import Triangle.AbstractSyntaxTrees.BinaryOperatorDeclaration;
-import Triangle.AbstractSyntaxTrees.BoolTypeDenoter;
-import Triangle.AbstractSyntaxTrees.CallCommand;
-import Triangle.AbstractSyntaxTrees.CallExpression;
-import Triangle.AbstractSyntaxTrees.CharTypeDenoter;
-import Triangle.AbstractSyntaxTrees.CharacterExpression;
-import Triangle.AbstractSyntaxTrees.CharacterLiteral;
-import Triangle.AbstractSyntaxTrees.ConstActualParameter;
-import Triangle.AbstractSyntaxTrees.ConstDeclaration;
-import Triangle.AbstractSyntaxTrees.ConstFormalParameter;
-import Triangle.AbstractSyntaxTrees.DotVname;
-import Triangle.AbstractSyntaxTrees.EmptyActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.EmptyCommand;
-import Triangle.AbstractSyntaxTrees.EmptyExpression;
-import Triangle.AbstractSyntaxTrees.EmptyFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.ErrorTypeDenoter;
-import Triangle.AbstractSyntaxTrees.FuncActualParameter;
-import Triangle.AbstractSyntaxTrees.FuncDeclaration;
-import Triangle.AbstractSyntaxTrees.FuncFormalParameter;
-import Triangle.AbstractSyntaxTrees.Identifier;
-import Triangle.AbstractSyntaxTrees.IfCommand;
-import Triangle.AbstractSyntaxTrees.IfExpression;
-import Triangle.AbstractSyntaxTrees.IntTypeDenoter;
-import Triangle.AbstractSyntaxTrees.IntegerExpression;
-import Triangle.AbstractSyntaxTrees.IntegerLiteral;
-import Triangle.AbstractSyntaxTrees.LetCommand;
-import Triangle.AbstractSyntaxTrees.LetExpression;
-import Triangle.AbstractSyntaxTrees.MultipleActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.MultipleArrayAggregate;
-import Triangle.AbstractSyntaxTrees.MultipleFieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.MultipleFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.MultipleRecordAggregate;
-import Triangle.AbstractSyntaxTrees.Operator;
-import Triangle.AbstractSyntaxTrees.ProcActualParameter;
-import Triangle.AbstractSyntaxTrees.ProcDeclaration;
-import Triangle.AbstractSyntaxTrees.ProcFormalParameter;
 import Triangle.AbstractSyntaxTrees.Program;
-import Triangle.AbstractSyntaxTrees.RecordExpression;
-import Triangle.AbstractSyntaxTrees.RecordTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SequentialCommand;
-import Triangle.AbstractSyntaxTrees.SequentialDeclaration;
-import Triangle.AbstractSyntaxTrees.SimpleTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SimpleVname;
-import Triangle.AbstractSyntaxTrees.SingleActualParameterSequence;
-import Triangle.AbstractSyntaxTrees.SingleArrayAggregate;
-import Triangle.AbstractSyntaxTrees.SingleFieldTypeDenoter;
-import Triangle.AbstractSyntaxTrees.SingleFormalParameterSequence;
-import Triangle.AbstractSyntaxTrees.SingleRecordAggregate;
-import Triangle.AbstractSyntaxTrees.SubscriptVname;
-import Triangle.AbstractSyntaxTrees.TypeDeclaration;
-import Triangle.AbstractSyntaxTrees.UnaryExpression;
-import Triangle.AbstractSyntaxTrees.UnaryOperatorDeclaration;
-import Triangle.AbstractSyntaxTrees.VarActualParameter;
-import Triangle.AbstractSyntaxTrees.VarDeclaration;
-import Triangle.AbstractSyntaxTrees.VarFormalParameter;
-import Triangle.AbstractSyntaxTrees.Visitor;
-import Triangle.AbstractSyntaxTrees.VnameExpression;
-import Triangle.AbstractSyntaxTrees.WhileCommand;
-
-public class LayoutVisitor implements Visitor {
+import Triangle.AbstractSyntaxTrees.Actuals.ConstActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.EmptyActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.FuncActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.MultipleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.ProcActualParameter;
+import Triangle.AbstractSyntaxTrees.Actuals.SingleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.Actuals.VarActualParameter;
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.MultipleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.Aggregates.SingleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Commands.AssignCommand;
+import Triangle.AbstractSyntaxTrees.Commands.CallCommand;
+import Triangle.AbstractSyntaxTrees.Commands.EmptyCommand;
+import Triangle.AbstractSyntaxTrees.Commands.IfCommand;
+import Triangle.AbstractSyntaxTrees.Commands.LetCommand;
+import Triangle.AbstractSyntaxTrees.Commands.SequentialCommand;
+import Triangle.AbstractSyntaxTrees.Commands.WhileCommand;
+import Triangle.AbstractSyntaxTrees.Declarations.BinaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ConstDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.FuncDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.ProcDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.SequentialDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.UnaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.Declarations.VarDeclaration;
+import Triangle.AbstractSyntaxTrees.Expressions.ArrayExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.BinaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CallExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.CharacterExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.EmptyExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.IfExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.IntegerExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.LetExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.RecordExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.UnaryExpression;
+import Triangle.AbstractSyntaxTrees.Expressions.VnameExpression;
+import Triangle.AbstractSyntaxTrees.Formals.ConstFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.EmptyFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.FuncFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.MultipleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.ProcFormalParameter;
+import Triangle.AbstractSyntaxTrees.Formals.SingleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.Formals.VarFormalParameter;
+import Triangle.AbstractSyntaxTrees.Terminals.CharacterLiteral;
+import Triangle.AbstractSyntaxTrees.Terminals.Identifier;
+import Triangle.AbstractSyntaxTrees.Terminals.IntegerLiteral;
+import Triangle.AbstractSyntaxTrees.Terminals.Operator;
+import Triangle.AbstractSyntaxTrees.Types.AnyTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.ArrayTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.BoolTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.CharTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.ErrorTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.IntTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.MultipleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.RecordTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SimpleTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.SingleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Types.TypeDeclaration;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterSequenceVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ActualParameterVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ArrayAggregateVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.CommandVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.DeclarationVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ExpressionVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterSequenceVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.FormalParameterVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.IdentifierVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.LiteralVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.OperatorVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.ProgramVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.RecordAggregateVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.TypeDenoterVisitor;
+import Triangle.AbstractSyntaxTrees.Visitors.VnameVisitor;
+import Triangle.AbstractSyntaxTrees.Vnames.DotVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SimpleVname;
+import Triangle.AbstractSyntaxTrees.Vnames.SubscriptVname;
+
+public class LayoutVisitor implements ActualParameterVisitor<Void, DrawingTree>,
+		ActualParameterSequenceVisitor<Void, DrawingTree>, ArrayAggregateVisitor<Void, DrawingTree>,
+		CommandVisitor<Void, DrawingTree>, DeclarationVisitor<Void, DrawingTree>, ExpressionVisitor<Void, DrawingTree>,
+		FormalParameterVisitor<Void, DrawingTree>, FormalParameterSequenceVisitor<Void, DrawingTree>,
+		IdentifierVisitor<Void, DrawingTree>, LiteralVisitor<Void, DrawingTree>, OperatorVisitor<Void, DrawingTree>,
+		ProgramVisitor<Void, DrawingTree>, RecordAggregateVisitor<Void, DrawingTree>,
+		TypeDenoterVisitor<Void, DrawingTree>, VnameVisitor<Void, DrawingTree> {
 
 	private final int BORDER = 5;
 	private final int PARENT_SEP = 30;
@@ -94,333 +113,427 @@ public class LayoutVisitor implements Visitor {
 
 	// Commands
 	@Override
-	public Object visitAssignCommand(AssignCommand ast, Object obj) {
-		return layoutBinary("AssignCom.", ast.V, ast.E);
+	public DrawingTree visitAssignCommand(AssignCommand ast, Void obj) {
+		var d1 = ast.V.visit(this);
+		var d2 = ast.E.visit(this);
+		return layoutBinary("AssignCom.", d1, d2);
 	}
 
 	@Override
-	public Object visitCallCommand(CallCommand ast, Object obj) {
-		return layoutBinary("CallCom.", ast.I, ast.APS);
+	public DrawingTree visitCallCommand(CallCommand ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.APS.visit(this);
+		return layoutBinary("CallCom.", d1, d2);
 	}
 
 	@Override
-	public Object visitEmptyCommand(EmptyCommand ast, Object obj) {
+	public DrawingTree visitEmptyCommand(EmptyCommand ast, Void obj) {
 		return layoutNullary("EmptyCom.");
 	}
 
 	@Override
-	public Object visitIfCommand(IfCommand ast, Object obj) {
-		return layoutTernary("IfCom.", ast.E, ast.C1, ast.C2);
+	public DrawingTree visitIfCommand(IfCommand ast, Void obj) {
+		var d1 = ast.E.visit(this);
+		var d2 = ast.C1.visit(this);
+		var d3 = ast.C2.visit(this);
+		return layoutTernary("IfCom.", d1, d2, d3);
 	}
 
 	@Override
-	public Object visitLetCommand(LetCommand ast, Object obj) {
-		return layoutBinary("LetCom.", ast.D, ast.C);
+	public DrawingTree visitLetCommand(LetCommand ast, Void obj) {
+		var d1 = ast.D.visit(this);
+		var d2 = ast.C.visit(this);
+		return layoutBinary("LetCom.", d1, d2);
 	}
 
 	@Override
-	public Object visitSequentialCommand(SequentialCommand ast, Object obj) {
-		return layoutBinary("Seq.Com.", ast.C1, ast.C2);
+	public DrawingTree visitSequentialCommand(SequentialCommand ast, Void obj) {
+		var d1 = ast.C1.visit(this);
+		var d2 = ast.C2.visit(this);
+		return layoutBinary("Seq.Com.", d1, d2);
 	}
 
 	@Override
-	public Object visitWhileCommand(WhileCommand ast, Object obj) {
-		return layoutBinary("WhileCom.", ast.E, ast.C);
+	public DrawingTree visitWhileCommand(WhileCommand ast, Void obj) {
+		var d1 = ast.E.visit(this);
+		var d2 = ast.C.visit(this);
+		return layoutBinary("WhileCom.", d1, d2);
 	}
 
 	// Expressions
 	@Override
-	public Object visitArrayExpression(ArrayExpression ast, Object obj) {
-		return layoutUnary("ArrayExpr.", ast.AA);
+	public DrawingTree visitArrayExpression(ArrayExpression ast, Void obj) {
+		var d1 = ast.AA.visit(this);
+		return layoutUnary("ArrayExpr.", d1);
 	}
 
 	@Override
-	public Object visitBinaryExpression(BinaryExpression ast, Object obj) {
-		return layoutTernary("Bin.Expr.", ast.E1, ast.O, ast.E2);
+	public DrawingTree visitBinaryExpression(BinaryExpression ast, Void obj) {
+		var d1 = ast.E1.visit(this);
+		var d2 = ast.O.visit(this);
+		var d3 = ast.E2.visit(this);
+		return layoutTernary("Bin.Expr.", d1, d2, d3);
 	}
 
 	@Override
-	public Object visitCallExpression(CallExpression ast, Object obj) {
-		return layoutBinary("CallExpr.", ast.I, ast.APS);
+	public DrawingTree visitCallExpression(CallExpression ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.APS.visit(this);
+		return layoutBinary("CallExpr.", d1, d2);
 	}
 
 	@Override
-	public Object visitCharacterExpression(CharacterExpression ast, Object obj) {
-		return layoutUnary("Char.Expr.", ast.CL);
+	public DrawingTree visitCharacterExpression(CharacterExpression ast, Void obj) {
+		var d1 = ast.CL.visit(this);
+		return layoutUnary("Char.Expr.", d1);
 	}
 
 	@Override
-	public Object visitEmptyExpression(EmptyExpression ast, Object obj) {
+	public DrawingTree visitEmptyExpression(EmptyExpression ast, Void obj) {
 		return layoutNullary("EmptyExpr.");
 	}
 
 	@Override
-	public Object visitIfExpression(IfExpression ast, Object obj) {
-		return layoutTernary("IfExpr.", ast.E1, ast.E2, ast.E3);
+	public DrawingTree visitIfExpression(IfExpression ast, Void obj) {
+		var d1 = ast.E1.visit(this);
+		var d2 = ast.E2.visit(this);
+		var d3 = ast.E3.visit(this);
+		return layoutTernary("IfExpr.", d1, d2, d3);
 	}
 
 	@Override
-	public Object visitIntegerExpression(IntegerExpression ast, Object obj) {
-		return layoutUnary("Int.Expr.", ast.IL);
+	public DrawingTree visitIntegerExpression(IntegerExpression ast, Void obj) {
+		var d1 = ast.IL.visit(this);
+		return layoutUnary("Int.Expr.", d1);
 	}
 
 	@Override
-	public Object visitLetExpression(LetExpression ast, Object obj) {
-		return layoutBinary("LetExpr.", ast.D, ast.E);
+	public DrawingTree visitLetExpression(LetExpression ast, Void obj) {
+		var d1 = ast.D.visit(this);
+		var d2 = ast.E.visit(this);
+		return layoutBinary("LetExpr.", d1, d2);
 	}
 
 	@Override
-	public Object visitRecordExpression(RecordExpression ast, Object obj) {
-		return layoutUnary("Rec.Expr.", ast.RA);
+	public DrawingTree visitRecordExpression(RecordExpression ast, Void obj) {
+		var d1 = ast.RA.visit(this);
+		return layoutUnary("Rec.Expr.", d1);
 	}
 
 	@Override
-	public Object visitUnaryExpression(UnaryExpression ast, Object obj) {
-		return layoutBinary("UnaryExpr.", ast.O, ast.E);
+	public DrawingTree visitUnaryExpression(UnaryExpression ast, Void obj) {
+		var d1 = ast.O.visit(this);
+		var d2 = ast.E.visit(this);
+		return layoutBinary("UnaryExpr.", d1, d2);
 	}
 
 	@Override
-	public Object visitVnameExpression(VnameExpression ast, Object obj) {
-		return layoutUnary("VnameExpr.", ast.V);
+	public DrawingTree visitVnameExpression(VnameExpression ast, Void obj) {
+		var d1 = ast.V.visit(this);
+		return layoutUnary("VnameExpr.", d1);
 	}
 
 	// Declarations
 	@Override
-	public Object visitBinaryOperatorDeclaration(BinaryOperatorDeclaration ast, Object obj) {
-		return layoutQuaternary("Bin.Op.Decl.", ast.O, ast.ARG1, ast.ARG2, ast.RES);
+	public DrawingTree visitBinaryOperatorDeclaration(BinaryOperatorDeclaration ast, Void obj) {
+		var d1 = ast.O.visit(this);
+		var d2 = ast.ARG1.visit(this);
+		var d3 = ast.ARG2.visit(this);
+		var d4 = ast.RES.visit(this);
+		return layoutQuaternary("Bin.Op.Decl.", d1, d2, d3, d4);
 	}
 
 	@Override
-	public Object visitConstDeclaration(ConstDeclaration ast, Object obj) {
-		return layoutBinary("ConstDecl.", ast.I, ast.E);
+	public DrawingTree visitConstDeclaration(ConstDeclaration ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.E.visit(this);
+		return layoutBinary("ConstDecl.", d1, d2);
 	}
 
 	@Override
-	public Object visitFuncDeclaration(FuncDeclaration ast, Object obj) {
-		return layoutQuaternary("FuncDecl.", ast.I, ast.FPS, ast.T, ast.E);
+	public DrawingTree visitFuncDeclaration(FuncDeclaration ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.FPS.visit(this);
+		var d3 = ast.T.visit(this);
+		var d4 = ast.E.visit(this);
+		return layoutQuaternary("FuncDecl.", d1, d2, d3, d4);
 	}
 
 	@Override
-	public Object visitProcDeclaration(ProcDeclaration ast, Object obj) {
-		return layoutTernary("ProcDecl.", ast.I, ast.FPS, ast.C);
+	public DrawingTree visitProcDeclaration(ProcDeclaration ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.FPS.visit(this);
+		var d3 = ast.C.visit(this);
+		return layoutTernary("ProcDecl.", d1, d2, d3);
 	}
 
 	@Override
-	public Object visitSequentialDeclaration(SequentialDeclaration ast, Object obj) {
-		return layoutBinary("Seq.Decl.", ast.D1, ast.D2);
+	public DrawingTree visitSequentialDeclaration(SequentialDeclaration ast, Void obj) {
+		var d1 = ast.D1.visit(this);
+		var d2 = ast.D2.visit(this);
+		return layoutBinary("Seq.Decl.", d1, d2);
 	}
 
 	@Override
-	public Object visitTypeDeclaration(TypeDeclaration ast, Object obj) {
-		return layoutBinary("TypeDecl.", ast.I, ast.T);
+	public DrawingTree visitTypeDeclaration(TypeDeclaration ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.T.visit(this);
+		return layoutBinary("TypeDecl.", d1, d2);
 	}
 
 	@Override
-	public Object visitUnaryOperatorDeclaration(UnaryOperatorDeclaration ast, Object obj) {
-		return layoutTernary("UnaryOp.Decl.", ast.O, ast.ARG, ast.RES);
+	public DrawingTree visitUnaryOperatorDeclaration(UnaryOperatorDeclaration ast, Void obj) {
+		var d1 = ast.O.visit(this);
+		var d2 = ast.ARG.visit(this);
+		var d3 = ast.RES.visit(this);
+		return layoutTernary("UnaryOp.Decl.", d1, d2, d3);
 	}
 
 	@Override
-	public Object visitVarDeclaration(VarDeclaration ast, Object obj) {
-		return layoutBinary("VarDecl.", ast.I, ast.T);
+	public DrawingTree visitVarDeclaration(VarDeclaration ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.T.visit(this);
+		return layoutBinary("VarDecl.", d1, d2);
 	}
 
 	// Array Aggregates
 	@Override
-	public Object visitMultipleArrayAggregate(MultipleArrayAggregate ast, Object obj) {
-		return layoutBinary("Mult.ArrayAgg.", ast.E, ast.AA);
+	public DrawingTree visitMultipleArrayAggregate(MultipleArrayAggregate ast, Void obj) {
+		var d1 = ast.E.visit(this);
+		var d2 = ast.AA.visit(this);
+		return layoutBinary("Mult.ArrayAgg.", d1, d2);
 	}
 
 	@Override
-	public Object visitSingleArrayAggregate(SingleArrayAggregate ast, Object obj) {
-		return layoutUnary("Sing.ArrayAgg.", ast.E);
+	public DrawingTree visitSingleArrayAggregate(SingleArrayAggregate ast, Void obj) {
+		var d1 = ast.E.visit(this);
+		return layoutUnary("Sing.ArrayAgg.", d1);
 	}
 
 	// Record Aggregates
 	@Override
-	public Object visitMultipleRecordAggregate(MultipleRecordAggregate ast, Object obj) {
-		return layoutTernary("Mult.Rec.Agg.", ast.I, ast.E, ast.RA);
+	public DrawingTree visitMultipleRecordAggregate(MultipleRecordAggregate ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.E.visit(this);
+		var d3 = ast.RA.visit(this);
+		return layoutTernary("Mult.Rec.Agg.", d1, d2, d3);
 	}
 
 	@Override
-	public Object visitSingleRecordAggregate(SingleRecordAggregate ast, Object obj) {
-		return layoutBinary("Sing.Rec.Agg.", ast.I, ast.E);
+	public DrawingTree visitSingleRecordAggregate(SingleRecordAggregate ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.E.visit(this);
+		return layoutBinary("Sing.Rec.Agg.", d1, d2);
 	}
 
 	// Formal Parameters
 	@Override
-	public Object visitConstFormalParameter(ConstFormalParameter ast, Object obj) {
-		return layoutBinary("ConstF.P.", ast.I, ast.T);
+	public DrawingTree visitConstFormalParameter(ConstFormalParameter ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.T.visit(this);
+		return layoutBinary("ConstF.P.", d1, d2);
 	}
 
 	@Override
-	public Object visitFuncFormalParameter(FuncFormalParameter ast, Object obj) {
-		return layoutTernary("FuncF.P.", ast.I, ast.FPS, ast.T);
+	public DrawingTree visitFuncFormalParameter(FuncFormalParameter ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.FPS.visit(this);
+		var d3 = ast.T.visit(this);
+		return layoutTernary("FuncF.P.", d1, d2, d3);
 	}
 
 	@Override
-	public Object visitProcFormalParameter(ProcFormalParameter ast, Object obj) {
-		return layoutBinary("ProcF.P.", ast.I, ast.FPS);
+	public DrawingTree visitProcFormalParameter(ProcFormalParameter ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.FPS.visit(this);
+		return layoutBinary("ProcF.P.", d1, d2);
 	}
 
 	@Override
-	public Object visitVarFormalParameter(VarFormalParameter ast, Object obj) {
-		return layoutBinary("VarF.P.", ast.I, ast.T);
+	public DrawingTree visitVarFormalParameter(VarFormalParameter ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.T.visit(this);
+		return layoutBinary("VarF.P.", d1, d2);
 	}
 
 	@Override
-	public Object visitEmptyFormalParameterSequence(EmptyFormalParameterSequence ast, Object obj) {
+	public DrawingTree visitEmptyFormalParameterSequence(EmptyFormalParameterSequence ast, Void obj) {
 		return layoutNullary("EmptyF.P.S.");
 	}
 
 	@Override
-	public Object visitMultipleFormalParameterSequence(MultipleFormalParameterSequence ast, Object obj) {
-		return layoutBinary("Mult.F.P.S.", ast.FP, ast.FPS);
+	public DrawingTree visitMultipleFormalParameterSequence(MultipleFormalParameterSequence ast, Void obj) {
+		var d1 = ast.FP.visit(this);
+		var d2 = ast.FPS.visit(this);
+		return layoutBinary("Mult.F.P.S.", d1, d2);
 	}
 
 	@Override
-	public Object visitSingleFormalParameterSequence(SingleFormalParameterSequence ast, Object obj) {
-		return layoutUnary("Sing.F.P.S.", ast.FP);
+	public DrawingTree visitSingleFormalParameterSequence(SingleFormalParameterSequence ast, Void obj) {
+		var d1 = ast.FP.visit(this);
+		return layoutUnary("Sing.F.P.S.", d1);
 	}
 
 	// Actual Parameters
 	@Override
-	public Object visitConstActualParameter(ConstActualParameter ast, Object obj) {
-		return layoutUnary("ConstA.P.", ast.E);
+	public DrawingTree visitConstActualParameter(ConstActualParameter ast, Void obj) {
+		var d1 = ast.E.visit(this);
+		return layoutUnary("ConstA.P.", d1);
 	}
 
 	@Override
-	public Object visitFuncActualParameter(FuncActualParameter ast, Object obj) {
-		return layoutUnary("FuncA.P.", ast.I);
+	public DrawingTree visitFuncActualParameter(FuncActualParameter ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		return layoutUnary("FuncA.P.", d1);
 	}
 
 	@Override
-	public Object visitProcActualParameter(ProcActualParameter ast, Object obj) {
-		return layoutUnary("ProcA.P.", ast.I);
+	public DrawingTree visitProcActualParameter(ProcActualParameter ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		return layoutUnary("ProcA.P.", d1);
 	}
 
 	@Override
-	public Object visitVarActualParameter(VarActualParameter ast, Object obj) {
-		return layoutUnary("VarA.P.", ast.V);
+	public DrawingTree visitVarActualParameter(VarActualParameter ast, Void obj) {
+		var d1 = ast.V.visit(this);
+		return layoutUnary("VarA.P.", d1);
 	}
 
 	@Override
-	public Object visitEmptyActualParameterSequence(EmptyActualParameterSequence ast, Object obj) {
+	public DrawingTree visitEmptyActualParameterSequence(EmptyActualParameterSequence ast, Void obj) {
 		return layoutNullary("EmptyA.P.S.");
 	}
 
 	@Override
-	public Object visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, Object obj) {
-		return layoutBinary("Mult.A.P.S.", ast.AP, ast.APS);
+	public DrawingTree visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, Void obj) {
+		var d1 = ast.AP.visit(this);
+		var d2 = ast.APS.visit(this);
+		return layoutBinary("Mult.A.P.S.", d1, d2);
 	}
 
 	@Override
-	public Object visitSingleActualParameterSequence(SingleActualParameterSequence ast, Object obj) {
-		return layoutUnary("Sing.A.P.S.", ast.AP);
+	public DrawingTree visitSingleActualParameterSequence(SingleActualParameterSequence ast, Void obj) {
+		var d1 = ast.AP.visit(this);
+		return layoutUnary("Sing.A.P.S.", d1);
 	}
 
 	// Type Denoters
 	@Override
-	public Object visitAnyTypeDenoter(AnyTypeDenoter ast, Object obj) {
+	public DrawingTree visitAnyTypeDenoter(AnyTypeDenoter ast, Void obj) {
 		return layoutNullary("any");
 	}
 
 	@Override
-	public Object visitArrayTypeDenoter(ArrayTypeDenoter ast, Object obj) {
-		return layoutBinary("ArrayTypeD.", ast.IL, ast.T);
+	public DrawingTree visitArrayTypeDenoter(ArrayTypeDenoter ast, Void obj) {
+		var d1 = ast.IL.visit(this);
+		var d2 = ast.T.visit(this);
+		return layoutBinary("ArrayTypeD.", d1, d2);
 	}
 
 	@Override
-	public Object visitBoolTypeDenoter(BoolTypeDenoter ast, Object obj) {
+	public DrawingTree visitBoolTypeDenoter(BoolTypeDenoter ast, Void obj) {
 		return layoutNullary("bool");
 	}
 
 	@Override
-	public Object visitCharTypeDenoter(CharTypeDenoter ast, Object obj) {
+	public DrawingTree visitCharTypeDenoter(CharTypeDenoter ast, Void obj) {
 		return layoutNullary("char");
 	}
 
 	@Override
-	public Object visitErrorTypeDenoter(ErrorTypeDenoter ast, Object obj) {
+	public DrawingTree visitErrorTypeDenoter(ErrorTypeDenoter ast, Void obj) {
 		return layoutNullary("error");
 	}
 
 	@Override
-	public Object visitSimpleTypeDenoter(SimpleTypeDenoter ast, Object obj) {
-		return layoutUnary("Sim.TypeD.", ast.I);
+	public DrawingTree visitSimpleTypeDenoter(SimpleTypeDenoter ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		return layoutUnary("Sim.TypeD.", d1);
 	}
 
 	@Override
-	public Object visitIntTypeDenoter(IntTypeDenoter ast, Object obj) {
+	public DrawingTree visitIntTypeDenoter(IntTypeDenoter ast, Void obj) {
 		return layoutNullary("int");
 	}
 
 	@Override
-	public Object visitRecordTypeDenoter(RecordTypeDenoter ast, Object obj) {
-		return layoutUnary("Rec.TypeD.", ast.FT);
+	public DrawingTree visitRecordTypeDenoter(RecordTypeDenoter ast, Void obj) {
+		var d1 = ast.FT.visit(this);
+		return layoutUnary("Rec.TypeD.", d1);
 	}
 
 	@Override
-	public Object visitMultipleFieldTypeDenoter(MultipleFieldTypeDenoter ast, Object obj) {
-		return layoutTernary("Mult.F.TypeD.", ast.I, ast.T, ast.FT);
+	public DrawingTree visitMultipleFieldTypeDenoter(MultipleFieldTypeDenoter ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.T.visit(this);
+		var d3 = ast.FT.visit(this);
+		return layoutTernary("Mult.F.TypeD.", d1, d2, d3);
 	}
 
 	@Override
-	public Object visitSingleFieldTypeDenoter(SingleFieldTypeDenoter ast, Object obj) {
-		return layoutBinary("Sing.F.TypeD.", ast.I, ast.T);
+	public DrawingTree visitSingleFieldTypeDenoter(SingleFieldTypeDenoter ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.T.visit(this);
+		return layoutBinary("Sing.F.TypeD.", d1, d2);
 	}
 
 	// Literals, Identifiers and Operators
 	@Override
-	public Object visitCharacterLiteral(CharacterLiteral ast, Object obj) {
+	public DrawingTree visitCharacterLiteral(CharacterLiteral ast, Void obj) {
 		return layoutNullary(ast.spelling);
 	}
 
 	@Override
-	public Object visitIdentifier(Identifier ast, Object obj) {
+	public DrawingTree visitIdentifier(Identifier ast, Void obj) {
 		return layoutNullary(ast.spelling);
 	}
 
 	@Override
-	public Object visitIntegerLiteral(IntegerLiteral ast, Object obj) {
+	public DrawingTree visitIntegerLiteral(IntegerLiteral ast, Void obj) {
 		return layoutNullary(ast.spelling);
 	}
 
 	@Override
-	public Object visitOperator(Operator ast, Object obj) {
+	public DrawingTree visitOperator(Operator ast, Void obj) {
 		return layoutNullary(ast.spelling);
 	}
 
 	// Value-or-variable names
 	@Override
-	public Object visitDotVname(DotVname ast, Object obj) {
-		return layoutBinary("DotVname", ast.I, ast.V);
+	public DrawingTree visitDotVname(DotVname ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		var d2 = ast.V.visit(this);
+		return layoutBinary("DotVname", d1, d2);
 	}
 
 	@Override
-	public Object visitSimpleVname(SimpleVname ast, Object obj) {
-		return layoutUnary("Sim.Vname", ast.I);
+	public DrawingTree visitSimpleVname(SimpleVname ast, Void obj) {
+		var d1 = ast.I.visit(this);
+		return layoutUnary("Sim.Vname", d1);
 	}
 
 	@Override
-	public Object visitSubscriptVname(SubscriptVname ast, Object obj) {
-		return layoutBinary("Sub.Vname", ast.V, ast.E);
+	public DrawingTree visitSubscriptVname(SubscriptVname ast, Void obj) {
+		var d1 = ast.V.visit(this);
+		var d2 = ast.E.visit(this);
+		return layoutBinary("Sub.Vname", d1, d2);
 	}
 
 	// Programs
 	@Override
-	public Object visitProgram(Program ast, Object obj) {
-		return layoutUnary("Program", ast.C);
+	public DrawingTree visitProgram(Program ast, Void obj) {
+		var d1 = ast.C.visit(this);
+		return layoutUnary("Program", d1);
 	}
 
 	private DrawingTree layoutCaption(String name) {
-		int w = fontMetrics.stringWidth(name) + 4;
-		int h = fontMetrics.getHeight() + 4;
+		var w = fontMetrics.stringWidth(name) + 4;
+		var h = fontMetrics.getHeight() + 4;
 		return new DrawingTree(name, w, h);
 	}
 
 	private DrawingTree layoutNullary(String name) {
-		DrawingTree dt = layoutCaption(name);
+		var dt = layoutCaption(name);
 		dt.contour.upper_tail = new Polyline(0, dt.height + 2 * BORDER, null);
 		dt.contour.upper_head = dt.contour.upper_tail;
 		dt.contour.lower_tail = new Polyline(-dt.width - 2 * BORDER, 0, null);
@@ -428,48 +541,38 @@ public class LayoutVisitor implements Visitor {
 		return dt;
 	}
 
-	private DrawingTree layoutUnary(String name, AST child1) {
-		DrawingTree dt = layoutCaption(name);
-		DrawingTree d1 = (DrawingTree) child1.visit(this, null);
+	private DrawingTree layoutUnary(String name, DrawingTree d1) {
+		var dt = layoutCaption(name);
 		dt.setChildren(new DrawingTree[] { d1 });
 		attachParent(dt, join(dt));
 		return dt;
 	}
 
-	private DrawingTree layoutBinary(String name, AST child1, AST child2) {
-		DrawingTree dt = layoutCaption(name);
-		DrawingTree d1 = (DrawingTree) child1.visit(this, null);
-		DrawingTree d2 = (DrawingTree) child2.visit(this, null);
+	private DrawingTree layoutBinary(String name, DrawingTree d1, DrawingTree d2) {
+		var dt = layoutCaption(name);
 		dt.setChildren(new DrawingTree[] { d1, d2 });
 		attachParent(dt, join(dt));
 		return dt;
 	}
 
-	private DrawingTree layoutTernary(String name, AST child1, AST child2, AST child3) {
-		DrawingTree dt = layoutCaption(name);
-		DrawingTree d1 = (DrawingTree) child1.visit(this, null);
-		DrawingTree d2 = (DrawingTree) child2.visit(this, null);
-		DrawingTree d3 = (DrawingTree) child3.visit(this, null);
+	private DrawingTree layoutTernary(String name, DrawingTree d1, DrawingTree d2, DrawingTree d3) {
+		var dt = layoutCaption(name);
 		dt.setChildren(new DrawingTree[] { d1, d2, d3 });
 		attachParent(dt, join(dt));
 		return dt;
 	}
 
-	private DrawingTree layoutQuaternary(String name, AST child1, AST child2, AST child3, AST child4) {
-		DrawingTree dt = layoutCaption(name);
-		DrawingTree d1 = (DrawingTree) child1.visit(this, null);
-		DrawingTree d2 = (DrawingTree) child2.visit(this, null);
-		DrawingTree d3 = (DrawingTree) child3.visit(this, null);
-		DrawingTree d4 = (DrawingTree) child4.visit(this, null);
+	private DrawingTree layoutQuaternary(String name, DrawingTree d1, DrawingTree d2, DrawingTree d3, DrawingTree d4) {
+		var dt = layoutCaption(name);
 		dt.setChildren(new DrawingTree[] { d1, d2, d3, d4 });
 		attachParent(dt, join(dt));
 		return dt;
 	}
 
 	private void attachParent(DrawingTree dt, int w) {
-		int y = PARENT_SEP;
-		int x2 = (w - dt.width) / 2 - BORDER;
-		int x1 = x2 + dt.width + 2 * BORDER - w;
+		var y = PARENT_SEP;
+		var x2 = (w - dt.width) / 2 - BORDER;
+		var x1 = x2 + dt.width + 2 * BORDER - w;
 
 		dt.children[0].offset.y = y + dt.height;
 		dt.children[0].offset.x = x1;
@@ -478,13 +581,13 @@ public class LayoutVisitor implements Visitor {
 	}
 
 	private int join(DrawingTree dt) {
-		int w, sum;
 
 		dt.contour = dt.children[0].contour;
-		sum = w = dt.children[0].width + 2 * BORDER;
+		var sum = dt.children[0].width + 2 * BORDER;
+		var w = sum;
 
-		for (int i = 1; i < dt.children.length; i++) {
-			int d = merge(dt.contour, dt.children[i].contour);
+		for (var i = 1; i < dt.children.length; i++) {
+			var d = merge(dt.contour, dt.children[i].contour);
 			dt.children[i].offset.x = d + w;
 			dt.children[i].offset.y = 0;
 			w = dt.children[i].width + 2 * BORDER;
@@ -494,15 +597,12 @@ public class LayoutVisitor implements Visitor {
 	}
 
 	private int merge(Polygon c1, Polygon c2) {
-		int x, y, total, d;
-		Polyline lower, upper, b;
-
-		x = y = total = 0;
-		upper = c1.lower_head;
-		lower = c2.upper_head;
+		int x = 0, y = 0, total = 0;
+		var upper = c1.lower_head;
+		var lower = c2.upper_head;
 
 		while (lower != null && upper != null) {
-			d = offset(x, y, lower.dx, lower.dy, upper.dx, upper.dy);
+			var d = offset(x, y, lower.dx, lower.dy, upper.dx, upper.dy);
 			x += d;
 			total += d;
 
@@ -518,11 +618,11 @@ public class LayoutVisitor implements Visitor {
 		}
 
 		if (lower != null) {
-			b = bridge(c1.upper_tail, 0, 0, lower, x, y);
+			var b = bridge(c1.upper_tail, 0, 0, lower, x, y);
 			c1.upper_tail = (b.link != null) ? c2.upper_tail : b;
 			c1.lower_tail = c2.lower_tail;
 		} else {
-			b = bridge(c2.lower_tail, x, y, upper, 0, 0);
+			var b = bridge(c2.lower_tail, x, y, upper, 0, 0);
 			if (b.link == null) {
 				c1.lower_tail = b;
 			}
@@ -534,53 +634,45 @@ public class LayoutVisitor implements Visitor {
 	}
 
 	private int offset(int p1, int p2, int a1, int a2, int b1, int b2) {
-		int d, s, t;
 
 		if (b2 <= p2 || p2 + a2 <= 0) {
 			return 0;
 		}
 
-		t = b2 * a1 - a2 * b1;
+		var t = b2 * a1 - a2 * b1;
 		if (t > 0) {
 			if (p2 < 0) {
-				s = p2 * a1;
-				d = s / a2 - p1;
+				var s = p2 * a1;
+				return Math.max(0, s / a2 - p1);
 			} else if (p2 > 0) {
-				s = p2 * b1;
-				d = s / b2 - p1;
+				var s = p2 * b1;
+				return Math.max(0, s / b2 - p1);
 			} else {
-				d = -p1;
+				return Math.max(0, -p1);
 			}
 		} else if (b2 < p2 + a2) {
-			s = (b2 - p2) * a1;
-			d = b1 - (p1 + s / a2);
+			var s = (b2 - p2) * a1;
+			return Math.max(0, b1 - (p1 + s / a2));
 		} else if (b2 > p2 + a2) {
-			s = (a2 + p2) * b1;
-			d = s / b2 - (p1 + a1);
+			var s = (a2 + p2) * b1;
+			return Math.max(0, s / b2 - (p1 + a1));
 		} else {
-			d = b1 - (p1 + a1);
-		}
-
-		if (d > 0) {
-			return d;
-		} else {
-			return 0;
+			return Math.max(0, b1 - (p1 + a1));
 		}
 	}
 
 	private Polyline bridge(Polyline line1, int x1, int y1, Polyline line2, int x2, int y2) {
-		int dy, dx, s;
-		Polyline r;
 
-		dy = y2 + line2.dy - y1;
+		int dx;
+		var dy = y2 + line2.dy - y1;
 		if (line2.dy == 0) {
 			dx = line2.dx;
 		} else {
-			s = dy * line2.dx;
+			var s = dy * line2.dx;
 			dx = s / line2.dy;
 		}
 
-		r = new Polyline(dx, dy, line2.link);
+		var r = new Polyline(dx, dy, line2.link);
 		line1.link = new Polyline(x2 + line2.dx - dx - x1, 0, r);
 
 		return r;