add basic virtual machine code

src/main.zig

@@ -4,6 +4,7 @@ const Allocator = std.mem.Allocator;
 
 // const Scanner = @import("scanner.zig").Scanner;
 const chunk = @import("chunk.zig");
+const vm = @import("vm.zig");
 
 //const Compiler = @import("compiler.zig").Compiler;
 
@@ -107,7 +108,7 @@ pub fn main() !void {
     var allocator = &arena.allocator;
 
     var stdout_file = try std.io.getStdOut();
-    const stdout = &stdout_file.outStream().stream;
+    var stdout = &stdout_file.outStream().stream;
 
     var chk = try chunk.Chunk.init(allocator);
 
@@ -115,11 +116,13 @@ pub fn main() !void {
     //var opcode_byte: u8 = @enumToInt(chunk.OpCode.Return);
     //try chk.write(chunk.OpCode.Return);
 
-    var i: usize = 0;
+    var constant = try chk.writeConstant(1.2, 123);
-    while (i < 260) : (i += 1) {
-        var constant = try chk.writeConstant(1.2, 123);
-    }
     try chk.write(chunk.OpCode.Return, 123);
-
     try chk.disassemble(stdout, "test chunk");
+
+    var vmach = vm.VM.init(stdout, &chk);
+
+    std.debug.warn("vm start\n");
+    _ = try vmach.interpret();
+    std.debug.warn("vm end\n");
 }

src/vm.zig

@@ -1,7 +1,78 @@
-const Chunk = @import("chunk.zig");
+const std = @import("std");
+const chunk = @import("chunk.zig");
+const value = @import("value.zig");
+
+const Chunk = chunk.Chunk;
+const StdOut = *std.io.OutStream(std.fs.File.WriteError);
+
+pub const InterpretResult = enum {
+    Ok,
+    CompileError,
+    RuntimeError,
+};
 
 pub const VM = struct {
-    chunk: *Chunk,
+    chk: *Chunk,
+    ip: usize,
+    stdout: StdOut,
 
-    pub fn init() VM {}
+    pub fn init(stdout: StdOut, chk: *Chunk) VM {
+        return VM{
+            .stdout = stdout,
+            .chk = chk,
+            .ip = 0,
+        };
+    }
+
+    fn readByte(self: *VM) u8 {
+        var byte: u8 = self.chk.code[self.ip];
+        self.ip += 1;
+        return byte;
+    }
+
+    fn readConst(self: *VM) value.Value {
+        return self.chk.constants.values[self.readByte()];
+    }
+
+    fn readConstLong(self: *VM) value.Value {
+        const v3 = self.readByte();
+        const v2 = self.readByte();
+        const v1 = self.readByte();
+        const const_idx = (@intCast(u24, v3) << 16) |
+            (@intCast(u24, v2) << 8) |
+            v1;
+
+        return self.chk.constants.values[const_idx];
+    }
+
+    fn run(self: *VM) !InterpretResult {
+        while (true) {
+            var instruction = self.readByte();
+
+            switch (instruction) {
+                chunk.OpCode.Constant => blk: {
+                    var constant = self.readConst();
+                    try value.printValue(self.stdout, constant);
+                    break :blk;
+                },
+                chunk.OpCode.ConstantLong => blk: {
+                    var constant = self.readConstLong();
+                    try value.printValue(self.stdout, constant);
+                    break :blk;
+                },
+                chunk.OpCode.Return => blk: {
+                    return InterpretResult.Ok;
+                },
+                else => blk: {
+                    std.debug.warn("Unknown instruction: {x}\n", instruction);
+                    return InterpretResult.RuntimeError;
+                },
+            }
+        }
+    }
+
+    pub fn interpret(self: *VM) !InterpretResult {
+        self.ip = 0;
+        return try self.run();
+    }
 };