A Virtual Machine 15

dub.sdl

@@ -5,15 +5,16 @@ copyright "Copyright © 2025, tanya"
 license "MPL-2.0"
 dependency "commandr" version="~>1.1.0"
 targetType "executable"
-buildRequirements "requireBoundsCheck" "requireContracts"
-
-versions "LoxConcatNonStrings" "LoxExtraNativeFuncs" "LoxPrintMultiple"
 
 sourcePaths
 configuration "clox" {
+	debugVersions "traceExec"
+	buildRequirements "requireBoundsCheck" "requireContracts"
 	sourcePaths "src/clox" "src/common"
 }
 configuration "jlox" {
+	versions "LoxConcatNonStrings" "LoxExtraNativeFuncs" "LoxPrintMultiple"
+	buildRequirements "requireBoundsCheck" "requireContracts"
 	sourcePaths "src/jlox" "src/common"
 }
 

src/clox/chunk.d

@@ -6,8 +6,10 @@ import std.stdio;
 import clox.value;
 
 enum OpCode : ubyte{
-	OP_CONSTANT,
-	OP_RETURN,
+	Constant,
+	Add, Subtract, Multiply, Divide,
+	Negate,
+	Return,
 }
 
 struct Chunk{

src/clox/dbg.d

@@ -1,41 +1,47 @@
 module clox.dbg;
 
 import std.stdio;
+import std.conv;
+import std.uni;
 
 import clox.chunk;
 import clox.value;
 
-private ulong simpleInstruction(string name, ulong offset){
-	writeln(name);
+debug private ulong simpleInstruction(string name, ulong offset) @nogc nothrow{
+	debug writeln(name);
 	return offset + 1;
 }
-private ulong constantInstruction(string name, in ref Chunk chunk, ulong offset){
+debug private ulong constantInstruction(string name, Chunk* chunk, ulong offset) @nogc nothrow{
 	ubyte constant = chunk.code[offset + 1];
-	writef("%-16s %4d '", name, constant);
-	printValue(chunk.constants[constant]);
-	writeln("'");
+	debug writef("%-16s %4d '", name, constant);
+	debug printValue(chunk.constants[constant]);
+	debug writeln("'");
 	return offset + 2;
 }
 
-void disassembleChunk(in ref Chunk chunk, string name = "chunk"){
-	writefln("== %s ==", name);
+debug void disassembleChunk(Chunk* chunk, string name = "chunk") @nogc nothrow{
+	debug writefln("== %s ==", name);
 	for(ulong offset = 0; offset < chunk.code.length;)
 		offset = disassembleInstruction(chunk, offset);
 }
-ulong disassembleInstruction(in ref Chunk chunk, const ulong offset){
-	writef(" %04d ", offset);
-	if(offset > 0 && chunk.lines[offset] == chunk.lines[offset - 1])
-		write("    | ");
-	else
-		writef(" %4d ", chunk.lines[offset]);
+debug ulong disassembleInstruction(Chunk* chunk, const ulong offset) @nogc nothrow{
+	debug writef(" %04d ", offset);
+	if(offset > 0 && chunk.lines[offset] == chunk.lines[offset - 1]){
+		debug write("    | ");
+	} else {
+		debug writef(" %4d ", chunk.lines[offset]);
+	}
 	ubyte instruction = chunk.code[offset];
 	with(OpCode) switch(instruction){
-		case OP_CONSTANT:
+		case Constant:
 			return constantInstruction("OP_CONSTANT", chunk, offset);
-		case OP_RETURN:
-			return simpleInstruction("OP_RETURN", offset);
+		static foreach(k; [ Return, Negate, Add, Subtract, Multiply, Divide ]){
+			case k:
+				static name = "OP_" ~ (k.to!string).toUpper;
+				return simpleInstruction(name, offset);
+		}
 		default:
-			writefln("Unknown opcode %d", instruction);
+			debug writefln("Unknown opcode %d", instruction);
 			return offset + 1;
 	}
 }

src/clox/main.d

@@ -4,17 +4,35 @@ import std.stdio;
 
 import clox.chunk;
 import clox.dbg;
+import clox.vm;
 
 int main(string[] argv){
 	Chunk chunk;
 
 	ubyte constant = chunk.addConstant(1.2);
-	chunk.write(OpCode.OP_CONSTANT);
+	chunk.write(OpCode.Constant);
 	chunk.write(constant);
 
-	chunk.write(OpCode.OP_RETURN);
+	constant = chunk.addConstant(3.4);
+	chunk.write(OpCode.Constant);
+	chunk.write(constant);
+
+	chunk.write(OpCode.Add);
+
+	constant = chunk.addConstant(5.6);
+	chunk.write(OpCode.Constant);
+	chunk.write(constant);
+
+	chunk.write(OpCode.Divide);
+
+	chunk.write(OpCode.Negate);
+
+	chunk.write(OpCode.Return);
+
+	VM vm = VM(0);
+	vm.interpret(&chunk);
+
 
-	disassembleChunk(chunk);
 	return 0;
 }
 

src/clox/util.d

@@ -0,0 +1,25 @@
+module clox.util;
+
+struct Stack(T, size_t N){
+	T* top;
+	T[N] data;
+	invariant{ assert(top <= data.ptr + N); assert(top >= data.ptr); }
+	this(int _) @nogc nothrow{
+		top = data.ptr;
+	}
+	void push(T value) @nogc nothrow{
+		assert(top < data.ptr + N);
+		debug assert(*top is T.init);
+		*(top++) = value;
+	}
+	T pop() @nogc nothrow{
+		assert(top > data.ptr);
+		T t = *(--top);
+		debug *(top) = T.init;
+		return t;
+	}
+	const(T)[] live() @nogc nothrow const{
+		return data[0 .. (top - data.ptr)];
+	}
+}
+

src/clox/value.d

@@ -4,7 +4,7 @@ import std.stdio;
 
 alias Value = double;
 
-void printValue(Value value){
-	writef("%g", value);
+debug void printValue(Value value) @nogc nothrow{
+	debug writef("%g", value);
 }
 

src/clox/vm.d

@@ -0,0 +1,59 @@
+module clox.vm;
+
+import std.stdio;
+
+import clox.chunk;
+import clox.value;
+import clox.dbg;
+import clox.util;
+
+enum stackMax = 256;
+
+struct VM{
+	const(ubyte)* ip;
+	Stack!(Value, stackMax) stack;
+	Chunk* chunk;
+	enum InterpretResult{ Ok, CompileError, RunetimeError }
+	this(int _) @nogc nothrow {
+		stack = typeof(stack)(0);
+	}
+	InterpretResult interpret(Chunk* chunk) @nogc nothrow {
+		this.chunk = chunk;
+		ip = &chunk.code[0];
+		return run();
+	}
+	private InterpretResult run() @nogc nothrow {
+		auto readByte() => *ip++;
+		auto readIns() => cast(OpCode)readByte();
+		auto readConstant() => chunk.constants[readByte()];
+		while(true){
+			debug(traceExec){
+				writeln("          ", stack.live);
+				debug disassembleInstruction(chunk, ip - &chunk.code[0]);
+			}
+			OpCode instruction = readIns();
+			with(OpCode) opSwitch: final switch(instruction){
+				case Constant:
+					Value constant = readConstant();
+					stack.push(constant);
+					break;
+				static foreach(k, op; [ Add: "+", Subtract: "-", Multiply: "*", Divide: "/" ]){
+					case k:
+						Value b = stack.pop();
+						Value a = stack.pop();
+						stack.push(mixin("a", op, "b"));
+						break opSwitch;
+				}
+				case Negate:
+					stack.push(-stack.pop());
+					break;
+				case Return:
+					debug printValue(stack.pop());
+					debug writeln();
+					return InterpretResult.Ok;
+			}
+		}
+		assert(0);
+	}
+}
+