implementing table optimization (ch30)

README.md

@@ -18,9 +18,9 @@ While reading [Crafting Interpreters](https://craftinginterpreters.com/), after
 - [x] 25 - Closures
 - [x] 26 - Garbage Collection
 - [x] 27 - Classes and Instances
-- [ ] 28 - Method and Initializers
-- [ ] 29 - Superclasses
-- [ ] 30 - Optimization
+- [x] 28 - Method and Initializers
+- [x] 29 - Superclasses
+- [x] 30 - Optimization (without NaN boxing/NaN tagging)
 
 ## Build & run
 

samples/ch28_initializers.lox

@@ -0,0 +1,14 @@
+class CoffeeMaker {
+    init(coffee) {
+        this.coffee = coffee;
+    }
+    brew() {
+        print "Enjoy your cup of " + this.coffee;
+        // No reusing the grounds!
+        this.coffee = nil;
+    }
+}
+
+var maker = CoffeeMaker("coffee and chicory");
+print maker;
+maker.brew();

samples/ch28_methods_again.lox

@@ -0,0 +1,12 @@
+class Brunch {
+    bacon() {
+        print "calling bacon()";
+    }
+    eggs() {
+        print "calling eggs()";
+    }
+}
+
+var brunch = Brunch();
+print brunch;
+brunch.bacon();

samples/ch28_methods_initializers.lox

@@ -1,8 +1,4 @@
 class Brunch {
-    bacon() {}
-    eggs() {}
+    init(food, drink) {}
 }
-
-var brunch = Brunch();
-print brunch;
-brunch.bacon();
+Brunch("eggs", "coffee");

samples/ch28_optimized_invocation.lox

@@ -0,0 +1,17 @@
+class Oops {
+    init() {
+        fun f() {
+            print "not a method";
+            return "returned value from f";
+        }
+        this.field = f;
+    }
+
+    blah() {
+        return "returned value from blah";
+    }
+}
+
+var oops = Oops();
+print oops.field();
+print oops.blah();

samples/ch29_superclass.lox

@@ -0,0 +1,21 @@
+class Doughnut {
+    cook() {
+        print "Dunk in the fryer.";
+    }
+
+    zzz() {
+        print "Bla";
+    }
+}
+
+class Cruller < Doughnut {
+    finish() {
+        print "Glaze with icing.";
+    }
+}
+
+var o2 = Cruller();
+o2.cook();
+o2.finish();
+
+

samples/ch29_superclass2.lox

@@ -0,0 +1,19 @@
+class A {
+    method() {
+        print "A method";
+    }
+}
+
+class B < A {
+    method() {
+        print "B method";
+    }
+
+    test() {
+        this.method();
+        super.method();
+    }
+}
+
+class C < B {}
+C().test();

samples/ch29_superclass_error.lox

@@ -0,0 +1,2 @@
+class Cake < Cake {
+}

samples/ch29_superclass_error2.lox

@@ -0,0 +1,2 @@
+var NotClass = "So not a class";
+class OhNo < NotClass {}

samples/ch8_initalizers.lox

@@ -0,0 +1,17 @@
+class Brunch {
+    var food;
+    var drink;
+
+    init(food, drink) {
+        this.food = food;
+        this.drink = drink;
+    }
+
+    fun get_recipe() {
+        return this.food + " " + this.drink;
+    }
+}
+
+var instance = Brunch("eggs", "coffee");
+print instance;
+print instance.get_recipe();

samples/indices.lox

@@ -0,0 +1,3 @@
+var alphabet = "abcdefghijklmnopqrstuvwxyz"; var X = alphabet; print "hello " + X[3] + X[0] + X[10];
+
+var s = "   "; s[0] = "d"; s[1] = "a"; s[2] = "k"; var hey = "hello " + s + "!"; print hey;

src/chunk.zig

@@ -73,18 +73,18 @@ pub const Chunk = struct {
         debug.print("== end of chunk dump \n\n", .{});
     }
 
-    pub fn dissassemble(self: Chunk, name: []const u8) void {
+    pub fn disassemble(self: Chunk, name: []const u8) void {
         debug.print("== {s} ==\n", .{name});
 
         var offset: usize = 0;
 
         while (offset < self.count) {
-            offset = self.dissassemble_instruction(offset);
+            offset = self.disassemble_instruction(offset);
         }
         debug.print("== end of {s} ==\n\n", .{name});
     }
 
-    pub fn dissassemble_instruction(self: Chunk, offset: usize) usize {
+    pub fn disassemble_instruction(self: Chunk, offset: usize) usize {
         var current_offset = offset;
         debug.print("{d:0>4} ", .{offset});
 
@@ -152,6 +152,12 @@ pub const Chunk = struct {
             @intFromEnum(OpCode.OP_GET_PROPERTY) => return utils.constant_instruction("OP_GET_PROPERTY", self, offset),
             @intFromEnum(OpCode.OP_SET_PROPERTY) => return utils.constant_instruction("OP_SET_PROPERTY", self, offset),
             @intFromEnum(OpCode.OP_METHOD) => return utils.constant_instruction("OP_METHOD", self, offset),
+            @intFromEnum(OpCode.OP_INDEX_GET) => return utils.simple_instruction("OP_INDEX_GET", offset),
+            @intFromEnum(OpCode.OP_INDEX_SET) => return utils.simple_instruction("OP_INDEX_SET", offset),
+            @intFromEnum(OpCode.OP_INVOKE) => return utils.invoke_instruction("OP_INVOKE", self, offset),
+            @intFromEnum(OpCode.OP_INHERIT) => return utils.simple_instruction("OP_INHERIT", offset),
+            @intFromEnum(OpCode.OP_GET_SUPER) => return utils.constant_instruction("OP_GET_SUPER", self, offset),
+            @intFromEnum(OpCode.OP_SUPER_INVOKE) => return utils.invoke_instruction("OP_SUPER_INVOKE", self, offset),
             else => {
                 debug.print("unknown opcode {d}\n", .{instruction});
                 return offset + 1;

src/compile.zig

@@ -29,6 +29,7 @@ const Precedence = enum {
     Term,
     Factor,
     Unary,
+    Index,
     Call,
     Primary,
 };
@@ -37,6 +38,7 @@ const ParserFn = *const fn (*Parser, bool) ParsingError!void;
 
 const ClassCompiler = struct {
     enclosing: ?*ClassCompiler,
+    has_super_class: bool,
 };
 
 const ParserRule = struct {
@@ -144,15 +146,26 @@ pub const Parser = struct {
     }
 
     fn emit_return(self: *Parser) ParsingError!void {
-        try self.emit_byte(@intFromEnum(OpCode.OP_NIL));
+        if (self.compiler.function_type == FunctionType.Initializer) {
+            try self.emit_bytes(@intFromEnum(OpCode.OP_GET_LOCAL), 0);
+        } else {
+            try self.emit_byte(@intFromEnum(OpCode.OP_NIL));
+        }
+
         try self.emit_byte(@intFromEnum(OpCode.OP_RETURN));
     }
 
     fn end_parser(self: *Parser) !*Obj.Function {
         try self.emit_return();
 
+        const compiler_function = self.compiler.function;
+
         if (!self.had_error and constants.DEBUG_PRINT_CODE) {
-            self.current_chunk().dissassemble("code");
+            var label: []const u8 = "<script>";
+            if (compiler_function.name != null) {
+                label = compiler_function.name.?.chars;
+            }
+            self.current_chunk().disassemble(label);
         }
 
         const function_obj = self.compiler.function;
@@ -201,6 +214,18 @@ pub const Parser = struct {
         self.consume(TokenType.RIGHT_PAREN, "Expect ')' after expression.");
     }
 
+    fn index_(self: *Parser, can_assign: bool) ParsingError!void {
+        try self.expression();
+        self.consume(TokenType.RIGHT_BRACKET, "Expecting ']");
+
+        if (can_assign and self.match(TokenType.EQUAL)) {
+            try self.expression();
+            try self.emit_byte(@intFromEnum(OpCode.OP_INDEX_SET));
+        } else {
+            try self.emit_byte(@intFromEnum(OpCode.OP_INDEX_GET));
+        }
+    }
+
     fn unary(self: *Parser, can_assign: bool) ParsingError!void {
         _ = can_assign;
 
@@ -262,6 +287,8 @@ pub const Parser = struct {
             TokenType.DOT => ParserRule{ .prefix = null, .infix = dot, .precedence = Precedence.Call },
             TokenType.MINUS => ParserRule{ .prefix = unary, .infix = binary, .precedence = Precedence.Term },
             TokenType.PLUS => ParserRule{ .prefix = null, .infix = binary, .precedence = Precedence.Term },
+            TokenType.LEFT_BRACKET => ParserRule{ .prefix = null, .infix = index_, .precedence = Precedence.Unary },
+            TokenType.RIGHT_BRACKET => ParserRule{ .prefix = null, .infix = null, .precedence = Precedence.None },
             TokenType.SEMICOLON => ParserRule{ .prefix = null, .infix = null, .precedence = Precedence.None },
             TokenType.SLASH => ParserRule{ .prefix = null, .infix = binary, .precedence = Precedence.Factor },
             TokenType.STAR => ParserRule{ .prefix = null, .infix = binary, .precedence = Precedence.Factor },
@@ -287,7 +314,7 @@ pub const Parser = struct {
             TokenType.OR => ParserRule{ .prefix = null, .infix = or_, .precedence = Precedence.Or },
             TokenType.PRINT => ParserRule{ .prefix = null, .infix = null, .precedence = Precedence.None },
             TokenType.RETURN => ParserRule{ .prefix = null, .infix = null, .precedence = Precedence.None },
-            TokenType.SUPER => ParserRule{ .prefix = null, .infix = null, .precedence = Precedence.None },
+            TokenType.SUPER => ParserRule{ .prefix = super_, .infix = null, .precedence = Precedence.None },
             TokenType.THIS => ParserRule{ .prefix = this_, .infix = null, .precedence = Precedence.None },
             TokenType.TRUE => ParserRule{ .prefix = literal, .infix = null, .precedence = Precedence.None },
             TokenType.VAR => ParserRule{ .prefix = null, .infix = null, .precedence = Precedence.None },
@@ -364,6 +391,17 @@ pub const Parser = struct {
             set_op = OpCode.OP_SET_GLOBAL;
         }
 
+        // handle assignments by index:
+        // - push value to the stack
+        // - modify it (through a OP_INDEX_SET)
+        // - update the variable
+        if (can_assign and self.match(TokenType.LEFT_BRACKET)) {
+            try self.emit_bytes(@intFromEnum(get_op), @intCast(arg));
+            try self.index_(can_assign);
+            try self.emit_bytes(@intFromEnum(set_op), @intCast(arg));
+            return;
+        }
+
         if (can_assign and self.match(TokenType.EQUAL)) {
             try self.expression();
             try self.emit_bytes(@intFromEnum(set_op), @intCast(arg));
@@ -865,6 +903,9 @@ pub const Parser = struct {
         if (self.match(TokenType.SEMICOLON)) {
             try self.emit_return();
         } else {
+            if (self.compiler.function_type == FunctionType.Initializer) {
+                self.error_msg("Can't return a value from an initialiaer");
+            }
             try self.expression();
             self.consume(TokenType.SEMICOLON, "Expect ';' after return value.");
             try self.emit_byte(@intFromEnum(OpCode.OP_RETURN));
@@ -883,9 +924,28 @@ pub const Parser = struct {
 
         var class_compiler = ClassCompiler{
             .enclosing = self.current_class_compiler(),
+            .has_super_class = false,
         };
         self.class_compiler = &class_compiler;
 
+        if (self.match(TokenType.LESS)) {
+            self.consume(TokenType.IDENTIFIER, "Expect superclass name.");
+            try self.variable(false);
+
+            if (identifiers_equals(class_name, self.previous.?)) {
+                self.error_msg("A class can't inherit from itself.");
+            }
+
+            self.begin_scope();
+            self.add_local(self.synthetic_token("super"));
+            try self.define_variable(0);
+
+            try self.named_variable(class_name, false);
+            try self.emit_byte(@intFromEnum(OpCode.OP_INHERIT));
+
+            self.current_class_compiler().?.has_super_class = true;
+        }
+
         try self.named_variable(class_name, false);
 
         self.consume(TokenType.LEFT_BRACE, "Expect '{' before class body.");
@@ -895,9 +955,23 @@ pub const Parser = struct {
         self.consume(TokenType.RIGHT_BRACE, "Expect '}' after class body.");
         try self.emit_byte(@intFromEnum(OpCode.OP_POP));
 
+        if (self.current_class_compiler().?.has_super_class) {
+            try self.end_scope();
+        }
+
         self.class_compiler = self.current_class_compiler().?.enclosing;
     }
 
+    fn synthetic_token(self: *Parser, text: []const u8) Token {
+        _ = self;
+        return Token{
+            .token_type = TokenType.EOF,
+            .start = text,
+            .length = text.len,
+            .line = 0,
+        };
+    }
+
     fn dot(self: *Parser, can_assign: bool) ParsingError!void {
         self.consume(TokenType.IDENTIFIER, "Expect property name after '.'.");
         const name = try self.identifier_constant(self.previous.?);
@@ -905,6 +979,10 @@ pub const Parser = struct {
         if (can_assign and self.match(TokenType.EQUAL)) {
             try self.expression();
             try self.emit_bytes(@intFromEnum(OpCode.OP_SET_PROPERTY), name);
+        } else if (self.match(TokenType.LEFT_PAREN)) {
+            const arg_count = try self.argument_list();
+            try self.emit_bytes(@intFromEnum(OpCode.OP_INVOKE), name);
+            try self.emit_byte(@intCast(arg_count));
         } else {
             try self.emit_bytes(@intFromEnum(OpCode.OP_GET_PROPERTY), name);
         }
@@ -914,7 +992,12 @@ pub const Parser = struct {
         self.consume(TokenType.IDENTIFIER, "Expect method name.");
         const constant = try self.identifier_constant(self.previous.?);
 
-        try self.function(FunctionType.Method);
+        var function_type: FunctionType = FunctionType.Method;
+        // std.debug.print("len: {d} {s}\n", .{self.previous.?.length, });
+        if (self.previous.?.length == 4 and std.mem.eql(u8, self.previous.?.start[0..4], "init")) {
+            function_type = FunctionType.Initializer;
+        }
+        try self.function(function_type);
         try self.emit_bytes(@intFromEnum(OpCode.OP_METHOD), constant);
     }
 
@@ -927,12 +1010,39 @@ pub const Parser = struct {
         _ = can_assign;
         try self.variable(false);
     }
+
+    fn super_(self: *Parser, can_assign: bool) ParsingError!void {
+        _ = can_assign;
+
+        if (self.current_class_compiler() == null) {
+            self.error_msg("Can't use 'super' outside of a class.");
+        } else if (!self.current_class_compiler().?.has_super_class) {
+            self.error_msg("Can't use 'super' in a class with no superclass.");
+        }
+
+        self.consume(TokenType.DOT, "Expect '.' after 'super'.");
+        self.consume(TokenType.IDENTIFIER, "Expect superclass method name.");
+        const name = try self.identifier_constant(self.previous.?);
+
+        try self.named_variable(self.synthetic_token("this"), false);
+
+        if (self.match(TokenType.LEFT_PAREN)) {
+            const arg_count = try self.argument_list();
+            try self.named_variable(self.synthetic_token("super"), false);
+            try self.emit_bytes(@intFromEnum(OpCode.OP_SUPER_INVOKE), name);
+            try self.emit_byte(@intCast(arg_count));
+        } else {
+            try self.named_variable(self.synthetic_token("super"), false);
+            try self.emit_bytes(@intFromEnum(OpCode.OP_GET_SUPER), name);
+        }
+    }
 };
 
 const FunctionType = enum {
     Function,
     Script,
     Method,
+    Initializer,
 };
 
 pub const Compiler = struct {

src/main.zig

@@ -72,7 +72,6 @@ pub fn main() !void {
     } else {
         vm.init_vm(allocator);
     }
-
     defer vm.destroy();
 
     if (args.len == 1) {

src/memory.zig

@@ -25,7 +25,7 @@ pub const ZloxAllocator = struct {
             .parent_allocator = parent_allocator,
             .vm = vm,
             .bytes_allocated = 0,
-            .next_gc = 1024,
+            .next_gc = 4096,
             .current_gc = false,
         };
     }
@@ -145,6 +145,8 @@ pub const ZloxAllocator = struct {
         self.mark_table(&self.vm.globals);
 
         self.mark_compiler_roots();
+
+        self.mark_object(&self.vm.init_string.?.obj);
     }
 
     pub fn mark_value(self: *Self, value: *Value) void {
@@ -264,6 +266,9 @@ pub const ZloxAllocator = struct {
         for (0..table.capacity) |idx| {
             const entry: *Entry = &table.entries[idx];
             if (entry.key != null and !entry.key.?.obj.is_marked) {
+                if (comptime constants.DEBUG_LOG_GC) {
+                    std.debug.print("GC: table_remove_white: deleting {s}\n", .{entry.key.?.chars});
+                }
                 _ = table.del(entry.key.?);
             }
         }
@@ -288,7 +293,7 @@ pub const ZloxAllocator = struct {
                     self.vm.objects = object;
                 }
 
-                if (comptime constants.DEBUG_LOG_GC == true) {
+                if (comptime constants.DEBUG_LOG_GC) {
                     std.debug.print("GC: sweeping {*}: ", .{unreached});
                     unreached.print();
                     std.debug.print("\n", .{});

src/opcode.zig

@@ -32,4 +32,10 @@ pub const OpCode = enum(u8) {
     OP_RETURN,
     OP_CLASS,
     OP_METHOD,
+    OP_INDEX_SET,
+    OP_INDEX_GET,
+    OP_INVOKE,
+    OP_INHERIT,
+    OP_GET_SUPER,
+    OP_SUPER_INVOKE,
 };

src/scanner.zig

@@ -6,6 +6,8 @@ pub const TokenType = enum {
     RIGHT_PAREN,
     LEFT_BRACE,
     RIGHT_BRACE,
+    LEFT_BRACKET,
+    RIGHT_BRACKET,
     COMMA,
     DOT,
     MINUS,
@@ -55,6 +57,8 @@ pub const TokenType = enum {
             TokenType.RIGHT_PAREN => "RIGHT_PAREN",
             TokenType.LEFT_BRACE => "LEFT_BRACE",
             TokenType.RIGHT_BRACE => "RIGHT_BRACE",
+            TokenType.LEFT_BRACKET => "LEFT_BRACKET",
+            TokenType.RIGHT_BRACKET => "RIGHT_BRACKET",
             TokenType.COMMA => "COMMA",
             TokenType.DOT => "DOT",
             TokenType.MINUS => "MINUS",
@@ -140,6 +144,8 @@ pub const Scanner = struct {
             ')' => self.make_token(TokenType.RIGHT_PAREN),
             '{' => self.make_token(TokenType.LEFT_BRACE),
             '}' => self.make_token(TokenType.RIGHT_BRACE),
+            '[' => self.make_token(TokenType.LEFT_BRACKET),
+            ']' => self.make_token(TokenType.RIGHT_BRACKET),
             ';' => self.make_token(TokenType.SEMICOLON),
             ',' => self.make_token(TokenType.COMMA),
             '.' => self.make_token(TokenType.DOT),

src/table.zig

@@ -61,11 +61,11 @@ pub const Table = struct {
 
     pub fn find_entry(entries: []Entry, key: *Obj.String) ?*Entry {
         var tombstone: ?*Entry = null;
-        var index = key.hash % entries.len;
+        // var index = key.hash % entries.len;
+        var index = key.hash & (entries.len - 1);
 
         while (true) {
             const entry = &entries[index];
-
             if (entry.key == null) {
                 if (entry.value.is_nil()) {
                     // Empty entry.
@@ -85,7 +85,8 @@ pub const Table = struct {
                 return entry;
             }
 
-            index = (index + 1) % entries.len;
+            // index = (index + 1) % entries.len;
+            index = (index + 1) & (entries.len - 1);
         }
     }
 
@@ -121,7 +122,7 @@ pub const Table = struct {
         std.debug.print("== Hash table count:{} capacity:{} ==\n", .{ self.count, self.capacity });
         for (self.entries, 0..) |entry, idx| {
             if (entry.key != null) {
-                std.debug.print("{d} ({d}) - {s}: ", .{ idx, entry.key.?.hash, entry.key.?.chars });
+                std.debug.print("{d} {*} (size: {d} hash:{d}) - {s}: ", .{ idx, entry.key, entry.key.?.chars.len, entry.key.?.hash, entry.key.?.chars });
                 entry.value.type_print();
                 std.debug.print("\n", .{});
             }
@@ -133,12 +134,12 @@ pub const Table = struct {
         std.debug.print("== End of hash table ==\n\n", .{});
     }
 
-    pub fn add_all(self: *Table, from: Table) void {
-        for (from.entries) |entry| {
+    pub fn add_all(self: *Table, to: *Table) void {
+        for (self.entries) |entry| {
             if (entry.key == null) {
                 continue;
             }
-            _ = self.set(entry.key.?, entry.value);
+            _ = to.set(entry.key.?, entry.value);
         }
     }
 
@@ -180,7 +181,8 @@ pub const Table = struct {
             return null;
         }
 
-        var index = hash % self.capacity;
+        // var index = hash % self.capacity;
+        var index = hash & (self.capacity - 1);
         while (true) {
             const entry = &self.entries[index];
             if (entry.key == null) {
@@ -192,7 +194,8 @@ pub const Table = struct {
                 return entry.key;
             }
 
-            index = (index + 1) % self.capacity;
+            // index = (index + 1) % self.capacity;
+            index = (index + 1) & (self.capacity - 1);
         }
     }
 };

src/utils.zig

@@ -55,3 +55,14 @@ pub fn identifiers_equals(a: Token, b: Token) bool {
 
     return std.mem.eql(u8, a.start[0..a.length], b.start[0..b.length]);
 }
+
+pub fn invoke_instruction(opcode_name: []const u8, chunk: Chunk, offset: usize) usize {
+    const constant = chunk.code[offset + 1];
+    const arg_count = chunk.code[offset + 2];
+
+    std.debug.print("{s:<16} ({d} args) {d:4} '", .{ opcode_name, arg_count, constant });
+    chunk.constants.values[constant].print();
+    std.debug.print("'\n", .{});
+
+    return offset + 3;
+}

src/vm.zig

@@ -49,6 +49,7 @@ pub const VM = struct {
     gray_count: usize,
     gray_capacity: usize,
     gray_stack: ?[]*Obj,
+    init_string: ?*Obj.String,
 
     pub fn new() VM {
         const vm = VM{
@@ -65,6 +66,7 @@ pub const VM = struct {
             .gray_capacity = 0,
             .gray_count = 0,
             .gray_stack = &.{},
+            .init_string = null,
         };
 
         return vm;
@@ -75,6 +77,9 @@ pub const VM = struct {
         self.globals = Table.new(self.allocator);
         self.strings = Table.new(self.allocator);
 
+        _ = try self.push(Value.obj_val(&self.copy_string("init").obj));
+        self.init_string = self.pop().as_string();
+
         self.define_native("clock", natives.clock);
         self.define_native("power", natives.power);
         self.define_native("str2num", natives.str2num);
@@ -88,6 +93,7 @@ pub const VM = struct {
 
         self.strings.destroy();
         self.globals.destroy();
+        self.init_string = null;
         self.destroy_objects();
 
         if (self.gray_stack != null) {
@@ -108,7 +114,9 @@ pub const VM = struct {
         var obj = self.objects;
         while (obj != null) {
             const obj_next = obj.?.next;
-            std.debug.print("OBJ: {*}\n", .{obj.?});
+            std.debug.print("OBJ: {*} {any}", .{ obj.?, obj.?.kind });
+            // obj.?.print();
+            std.debug.print("\n", .{});
             obj = obj_next;
         }
     }
@@ -148,7 +156,7 @@ pub const VM = struct {
                     }
                     debug.print("\n", .{});
                 }
-                _ = self.current_chunk().dissassemble_instruction(self.current_frame().ip);
+                _ = self.current_chunk().disassemble_instruction(self.current_frame().ip);
             }
 
             const instruction = self.read_byte();
@@ -330,6 +338,76 @@ pub const VM = struct {
                 @intFromEnum(OpCode.OP_METHOD) => {
                     self.define_method(self.read_constant().as_string());
                 },
+                @intFromEnum(OpCode.OP_INDEX_GET) => {
+                    if (!self.peek(0).is_number() or !self.peek(1).is_string()) {
+                        self.runtime_error("A number and a string are required for indexes.");
+                        return InterpretResult.RUNTIME_ERROR;
+                    }
+                    const index_val = self.pop();
+                    const value = self.pop();
+
+                    const index: usize = @as(usize, @intFromFloat(index_val.as_number()));
+                    if (index >= value.as_cstring().len) {
+                        self.runtime_error("The index must be set between 0 and string len.");
+                        return InterpretResult.RUNTIME_ERROR;
+                    }
+                    const c = value.as_cstring()[index .. index + 1];
+
+                    _ = try self.push(Value.obj_val(&self.copy_string(c).obj));
+                },
+                @intFromEnum(OpCode.OP_INDEX_SET) => {
+                    const value = self.pop();
+                    const index_val = self.pop();
+                    const origin = self.pop();
+
+                    if (!value.is_string() or value.as_cstring().len != 1) {
+                        self.runtime_error("Value to assign must be one byte.");
+                        return InterpretResult.RUNTIME_ERROR;
+                    }
+
+                    const index: usize = @as(usize, @intFromFloat(index_val.as_number()));
+
+                    var str = self.allocator.dupe(u8, origin.as_cstring()) catch unreachable;
+                    str[index] = value.as_cstring()[0];
+
+                    _ = try self.push(Value.obj_val(&self.take_string(str).obj));
+                },
+                @intFromEnum(OpCode.OP_INVOKE) => {
+                    const method = self.read_constant().as_string();
+                    const arg_count = self.read_byte();
+                    if (!self.invoke(method, arg_count)) {
+                        return InterpretResult.RUNTIME_ERROR;
+                    }
+                },
+                @intFromEnum(OpCode.OP_INHERIT) => {
+                    const superclass = self.peek(1);
+                    const subclass = self.peek(0).as_obj().as_class();
+
+                    if (!superclass.is_obj() or !superclass.as_obj().is_class()) {
+                        self.runtime_error("Superclass must be a class.");
+                        return InterpretResult.RUNTIME_ERROR;
+                    }
+
+                    superclass.as_obj().as_class().methods.add_all(&subclass.methods);
+                    _ = self.pop(); // subclass
+                },
+                @intFromEnum(OpCode.OP_GET_SUPER) => {
+                    const name: *Obj.String = self.read_constant().as_string();
+                    const superclass = self.pop().as_obj().as_class();
+
+                    if (!self.bind_method(superclass, name)) {
+                        return InterpretResult.RUNTIME_ERROR;
+                    }
+                },
+                @intFromEnum(OpCode.OP_SUPER_INVOKE) => {
+                    const method = self.read_constant().as_string();
+                    const arg_count = self.read_byte();
+                    const superclass = self.pop().as_obj().as_class();
+
+                    if (!self.invoke_from_class(superclass, method, arg_count)) {
+                        return InterpretResult.RUNTIME_ERROR;
+                    }
+                },
                 else => {
                     debug.print("Invalid instruction: {d}\n", .{instruction});
                     return InterpretResult.RUNTIME_ERROR;
@@ -500,6 +578,14 @@ pub const VM = struct {
                     const class = callee.as_obj().as_class();
                     self.stack[self.stack_top - arg_count - 1] = Value.obj_val(&Obj.Instance.new(self, class).obj);
 
+                    var initializer = Value.nil_val();
+
+                    if (class.methods.get(self.init_string.?, &initializer) == true) {
+                        return self.call(initializer.as_obj().as_closure(), arg_count);
+                    } else if (arg_count != 0) {
+                        self.runtime_error("Expected 0 arguments."); // XXX show number of arguments.
+                    }
+
                     return true;
                 },
                 ObjType.BoundMethod => {
@@ -518,7 +604,10 @@ pub const VM = struct {
         var method: Value = Value.nil_val();
 
         if (!class.methods.get(name, &method)) {
-            self.runtime_error("Undefined property."); // XXX add name.chars as '%s'.
+            const err_msg = std.fmt.allocPrint(self.allocator, "Undefined property '{s}'.", .{name.chars}) catch unreachable;
+            defer self.allocator.free(err_msg);
+            self.runtime_error(err_msg);
+
             return false;
         }
 
@@ -531,8 +620,9 @@ pub const VM = struct {
 
     pub fn call(self: *VM, closure: *Obj.Closure, arg_count: usize) bool {
         if (arg_count != closure.function.arity) {
-            self.runtime_error("Invalid argument count.");
-            // runtimeError("Expected %d arguments but got %d.", function->arity, argCount);
+            const err_msg = std.fmt.allocPrint(self.allocator, "Expected {d} arguments but got {d}.", .{ closure.function.arity, arg_count }) catch unreachable;
+            defer self.allocator.free(err_msg);
+            self.runtime_error(err_msg);
             return false;
         }
 
@@ -603,4 +693,30 @@ pub const VM = struct {
         _ = class.methods.set(name, method);
         _ = self.pop();
     }
+
+    fn invoke(self: *VM, name: *Obj.String, arg_count: usize) bool {
+        const receiver = self.peek(arg_count);
+        const instance = receiver.as_obj().as_instance();
+
+        var value = Value.nil_val();
+        if (instance.fields.get(name, &value)) {
+            self.stack[self.stack_top - arg_count - 1] = value;
+
+            return self.call_value(value, arg_count);
+        }
+
+        return self.invoke_from_class(instance.class, name, arg_count);
+    }
+
+    fn invoke_from_class(self: *VM, class: *Obj.Class, name: *Obj.String, arg_count: usize) bool {
+        var method = Value.nil_val();
+        if (!class.methods.get(name, &method)) {
+            const err_msg = std.fmt.allocPrint(self.allocator, "Undefined property '{s}'.", .{name.chars}) catch unreachable;
+            defer self.allocator.free(err_msg);
+            self.runtime_error(err_msg);
+            return false;
+        }
+
+        return self.call(method.as_obj().as_closure(), arg_count);
+    }
 };