From e921a0dda85ec80bfdae61e2e203848f7e24a978 Mon Sep 17 00:00:00 2001
From: Araozu <fernando@araozu.dev>
Date: Mon, 27 May 2024 21:08:29 -0500
Subject: [PATCH] VM simple execution

---
 src/chunk.zig |  5 +++--
 src/main.zig  | 14 +++++++++++++
 src/vm.zig    | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 73 insertions(+), 2 deletions(-)
 create mode 100644 src/vm.zig

diff --git a/src/chunk.zig b/src/chunk.zig
index bf1257e..1c50b84 100644
--- a/src/chunk.zig
+++ b/src/chunk.zig
@@ -55,6 +55,7 @@ pub const Chunk = struct {
 
     /// Prints the value of a single instruction
     fn dissasemble_instruction(self: *Chunk, offset: usize) usize {
+        // Print the instruction offset
         print("{d:0>4} ", .{offset});
 
         // Print the line number
@@ -65,7 +66,7 @@ pub const Chunk = struct {
         }
 
         const instruction = self.code[offset];
-        switch (instruction) {
+        switch (self.code[offset]) {
             @intFromEnum(OpCode.OP_RETURN) => return simple_instruction("OP_RETURN", offset),
             @intFromEnum(OpCode.OP_CONSTANT) => return self.constant_instruction("OP_CONSTANT", offset),
             else => {
@@ -102,7 +103,7 @@ fn simple_instruction(comptime name: []const u8, offset: usize) usize {
     return offset + 1;
 }
 
-fn print_value(v: value.Value) void {
+pub fn print_value(v: value.Value) void {
     print("{d}", .{v});
 }
 
diff --git a/src/main.zig b/src/main.zig
index 9679336..01d2576 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,6 +1,7 @@
 const std = @import("std");
 const chunk = @import("./chunk.zig");
 const OpCode = chunk.OpCode;
+const VM = @import("./vm.zig").VM;
 
 pub fn main() !void {
     // Prints to stderr (it's a shortcut based on `std.io.getStdErr()`)
@@ -19,12 +20,25 @@ pub fn main() !void {
     try c.write(@intFromEnum(chunk.OpCode.OP_RETURN), 1);
 
     c.dissasemble_chunk("test chunk");
+
+    std.debug.print("\n=== end of chunk creation ===\n\n", .{});
+
+    var vm = VM.init(alloc, &c);
+    defer vm.deinit();
+
+    _ = vm.run();
 }
 
 test "chunk test" {
     var c = try chunk.Chunk.init(std.testing.allocator);
     defer c.deinit();
 
+    const constant_idx = try c.add_constant(1.2);
+    try c.write(@intFromEnum(OpCode.OP_CONSTANT), 1);
+    try c.write(@truncate(constant_idx), 1);
+
+    try c.write(@intFromEnum(chunk.OpCode.OP_RETURN), 1);
+
     try c.write('a', 0);
     try c.write('b', 1);
     try c.write('J', 2);
diff --git a/src/vm.zig b/src/vm.zig
new file mode 100644
index 0000000..452fb8d
--- /dev/null
+++ b/src/vm.zig
@@ -0,0 +1,56 @@
+const std = @import("std");
+const chunk_mod = @import("./chunk.zig");
+const Chunk = chunk_mod.Chunk;
+const OpCode = chunk_mod.OpCode;
+const print = std.debug.print;
+
+const InterpretResult = enum {
+    Ok,
+    CompileError,
+    RuntimeError,
+};
+
+pub const VM = struct {
+    chunk: *Chunk,
+    ip: [*]const u8,
+    allocator: std.mem.Allocator,
+
+    // Takes ownership of the passed Chunk. This chunk will be deinitialized
+    // when this VM is deinitialized
+    pub fn init(allocator: std.mem.Allocator, chunk: *Chunk) VM {
+        return .{
+            .allocator = allocator,
+            .chunk = chunk,
+            .ip = chunk.code.ptr,
+        };
+    }
+
+    // Executes the instructions in the bytecode
+    pub fn run(self: *VM) InterpretResult {
+        while (true) {
+            const next = self.ip[0];
+            self.ip += 1;
+            switch (next) {
+                @intFromEnum(OpCode.OP_RETURN) => {
+                    return InterpretResult.Ok;
+                },
+                @intFromEnum(OpCode.OP_CONSTANT) => {
+                    const constant = self.chunk.constants.values[self.ip[0]];
+                    self.ip += 1;
+                    chunk_mod.print_value(constant);
+                    print("\n", .{});
+                },
+                else => {
+                    std.debug.print("Not implemented!\n", .{});
+                    unreachable;
+                },
+            }
+        }
+
+        return null;
+    }
+
+    pub fn deinit(self: VM) void {
+        _ = self;
+    }
+};