From ae665d89ed88431f690a8c6440ff4b2e745f586d Mon Sep 17 00:00:00 2001
From: zongor <admin@alfrescocavern.com>
Date: Sun, 4 May 2025 14:51:38 -0400
Subject: [PATCH] migrate old compiler, hack on that instead

---
 docs/SPECIFICATION.org |  52 +--
 src/chunk.c            |  19 +-
 src/chunk.h            |  32 +-
 src/common.h           |  13 +-
 src/compiler.c         | 869 +++++++++++++++++++++++++++++++++++------
 src/compiler.h         |   8 +-
 src/debug.c            | 155 ++++++--
 src/debug.h            |   4 +-
 src/main.c             |  20 +-
 src/memory.c           | 237 ++++++++++-
 src/memory.h           |  17 +-
 src/object.c           | 163 ++++++++
 src/object.h           | 114 ++++++
 src/scanner.c          | 265 +++++++------
 src/scanner.h          |   7 +-
 src/table.c            | 151 +++++++
 src/table.h            |  29 ++
 src/value.c            |  12 +-
 src/value.h            |  39 +-
 src/vm.c               | 522 +++++++++++++++++++++----
 src/vm.h               |  39 +-
 21 files changed, 2300 insertions(+), 467 deletions(-)
 create mode 100644 src/object.c
 create mode 100644 src/object.h
 create mode 100644 src/table.c
 create mode 100644 src/table.h

diff --git a/docs/SPECIFICATION.org b/docs/SPECIFICATION.org
index 345392a..6505828 100644
--- a/docs/SPECIFICATION.org
+++ b/docs/SPECIFICATION.org
@@ -1,4 +1,4 @@
-* /ztl/ (zongors transpiler language) Design parameters
+* /ZTL/ (Zongors Transpiler Language) Design parameters
 :PROPERTIES:
 :CUSTOM_ID: ztl-zongors-transpiler-language-design-parameters
 :END:
@@ -12,7 +12,7 @@ systems. /ztl/ also can "run" standalone inside of a lua vm for
 debugging purposes, it could be used for small scripting tasks or the
 like.
 
-* /ztl/ Grammar and Specification
+* /ZTL/ Grammar and Specification
 :PROPERTIES:
 :CUSTOM_ID: ztl-grammar-and-specification
 :END:
@@ -33,7 +33,7 @@ type «token» {
 }
 #+end_src ztl
 
-* Substantial Types
+* Basic Types
 :PROPERTIES:
 :CUSTOM_ID: substantial-types
 :END:
@@ -41,39 +41,9 @@ type «token» {
 :PROPERTIES:
 :CUSTOM_ID: numeric
 :END:
-*** bit (or unsigned units)
-:PROPERTIES:
-:CUSTOM_ID: bit-or-unsigned-units
-:END:
-- =u8=
+- =byte=
   - unsigned 8 bit integer (uint8_t)
-- =u16=
-  - unsigned 16 bit integer (uint16_t)
-- =u32=
-  - unsigned 32 bit integer (uint32_t)
-- =u64=
-  - unsigned 64 bit integer (uint64_t)
-
-*** integer (signed)
-:PROPERTIES:
-:CUSTOM_ID: integer-signed
-:END:
-- =i8=
-  - signed 8 bit integer (int8_t)
-- =i16=
-  - signed 16 bit integer (int16_t)
-- =i32=
-  - signed 32 bit integer (int32_t)
-- =i64=
-  - signed 64 bit integer (int64_t)
-
-*** real
-:PROPERTIES:
-:CUSTOM_ID: real
-:END:
-- =f32=
-  - 32 bit floating point (float)
-- =f64=
+- =number=
   - 64 bit floating point (double)
 
 ** string
@@ -157,8 +127,6 @@ The following is a list of global operators and their effect:
 
 - =//=
   - comment
-- =/**/=
-  - block comment
 - =??=
   - unwrap or
 - =+=
@@ -205,14 +173,8 @@ The following is a list of global operators and their effect:
 :PROPERTIES:
 :CUSTOM_ID: logical-bitwise-operators
 :END:
-- =eq=
-  - equal to
-- =ne=
-  - not equals to
 - =mod=
   - modulo
-- =not=
-  - logical not
 - =and=
   - logical and
 - =or=
@@ -255,10 +217,6 @@ if («token» is i32) {
 
 also used for letting constants
 
-#+begin_src ztl
-const PURPLE is Color(255, 255, 0);
-#+end_src ztl
-
 =as=
 
 coerces a type as another type if possible
diff --git a/src/chunk.c b/src/chunk.c
index 1d86f26..8eddb39 100644
--- a/src/chunk.c
+++ b/src/chunk.c
@@ -1,16 +1,16 @@
-#include <stdlib.h>
-
 #include "chunk.h"
+#include "memory.h"
+#include "vm.h"
 
-void newChunk(Chunk* chunk) {
+void initChunk(Chunk* chunk) {
   chunk->count = 0;
   chunk->capacity = 0;
-  chunk->code = NULL;
   chunk->lines = NULL;
-  newValueArray(&chunk->constants);
+  chunk->code = NULL;
+  initValueArray(&chunk->constants);
 }
 
-void writeChunk(Chunk *chunk, uint8_t byte, int line) {
+void writeChunk(Chunk* chunk, uint8_t byte, int line) {
   if (chunk->capacity < chunk->count + 1) {
     int oldCapacity = chunk->capacity;
     chunk->capacity = GROW_CAPACITY(oldCapacity);
@@ -25,15 +25,16 @@ void writeChunk(Chunk *chunk, uint8_t byte, int line) {
   chunk->count++;
 }
 
-void freeChunk(Chunk *chunk) {
+void freeChunk(Chunk* chunk) {
   FREE_ARRAY(uint8_t, chunk->code, chunk->capacity);
-  FREE_ARRAY(int, chunk->lines, chunk->capacity);
   freeValueArray(&chunk->constants);
-  newChunk(chunk);
+  initChunk(chunk);
 }
 
 int addConstant(Chunk* chunk, Value value) {
+  push(value);
   writeValueArray(&chunk->constants, value);
+  pop();
   return chunk->constants.count - 1;
 }
 
diff --git a/src/chunk.h b/src/chunk.h
index 563a80c..122ea0e 100644
--- a/src/chunk.h
+++ b/src/chunk.h
@@ -1,16 +1,24 @@
-#ifndef ztl_chunk_h
-#define ztl_chunk_h
+#ifndef zlc_chunk_h
+#define zlc_chunk_h
 
 #include "common.h"
-#include "memory.h"
 #include "value.h"
 
 typedef enum {
-  OP_NOOP,
   OP_CONSTANT,
   OP_NIL,
   OP_TRUE,
   OP_FALSE,
+  OP_POP,
+  OP_GET_LOCAL,
+  OP_GET_GLOBAL,
+  OP_DEFINE_GLOBAL,
+  OP_SET_LOCAL,
+  OP_SET_GLOBAL,
+  OP_GET_UPVALUE,
+  OP_SET_UPVALUE,
+  OP_GET_PROPERTY,
+  OP_SET_PROPERTY,
   OP_EQUAL,
   OP_GREATER,
   OP_LESS,
@@ -20,10 +28,20 @@ typedef enum {
   OP_DIVIDE,
   OP_NOT,
   OP_NEGATE,
-  OP_RETURN, 
+  OP_PRINT,
+  OP_JUMP,
+  OP_JUMP_IF_FALSE,
+  OP_LOOP,
+  OP_CALL,
+  OP_INVOKE,
+  OP_CLOSURE,
+  OP_CLOSE_UPVALUE,
+  OP_RETURN,
+  OP_TYPE,
+  OP_METHOD
 } OpCode;
 
-typedef struct Chunk {
+typedef struct {
   int count;
   int capacity;
   uint8_t *code;
@@ -31,7 +49,7 @@ typedef struct Chunk {
   ValueArray constants;
 } Chunk;
 
-void newChunk(Chunk *chunk);
+void initChunk(Chunk *chunk);
 void freeChunk(Chunk *chunk);
 void writeChunk(Chunk *chunk, uint8_t byte, int line);
 int addConstant(Chunk *chunk, Value value);
diff --git a/src/common.h b/src/common.h
index 98d48b6..5368a37 100644
--- a/src/common.h
+++ b/src/common.h
@@ -1,11 +1,16 @@
-#ifndef ztl_common_h
-#define ztl_common_h
+#ifndef zlc_common_h
+#define zlc_common_h
 
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
 
-#define DEBUG_TRACE_EXECUTION
-#define DEBUG_PRINT_CODE
+/* #define DEBUG_TRACE_EXECUTION */
+/* #define DEBUG_PRINT_CODE */
+
+/* #define DEBUG_STRESS_GC */
+/* #define DEBUG_LOG_GC */
+
+#define UINT8_COUNT (UINT8_MAX + 1)
 
 #endif
diff --git a/src/compiler.c b/src/compiler.c
index 9416a3e..780ba66 100644
--- a/src/compiler.c
+++ b/src/compiler.c
@@ -1,8 +1,10 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include "common.h"
 #include "compiler.h"
+#include "memory.h"
 #include "scanner.h"
 
 #ifdef DEBUG_PRINT_CODE
@@ -18,19 +20,19 @@ typedef struct {
 
 typedef enum {
   PREC_NONE,
-  PREC_ASSIGNMENT,  // =
-  PREC_OR,          // or
-  PREC_AND,         // and
-  PREC_EQUALITY,    // == !=
-  PREC_COMPARISON,  // < > <= >=
-  PREC_TERM,        // + -
-  PREC_FACTOR,      // * /
-  PREC_UNARY,       // ! -
-  PREC_CALL,        // . ()
+  PREC_ASSIGNMENT, // =
+  PREC_OR,         // or
+  PREC_AND,        // and
+  PREC_EQUALITY,   // == !=
+  PREC_COMPARISON, // < > <= >=
+  PREC_TERM,       // + -
+  PREC_FACTOR,     // * /
+  PREC_UNARY,      // ! -
+  PREC_CALL,       // . ()
   PREC_PRIMARY
 } Precedence;
 
-typedef void (*ParseFn)();
+typedef void (*ParseFn)(bool canAssign);
 
 typedef struct {
   ParseFn prefix;
@@ -38,15 +40,47 @@ typedef struct {
   Precedence precedence;
 } ParseRule;
 
+typedef struct {
+  Token name;
+  int depth;
+  bool isCaptured;
+} Local;
+
+typedef struct {
+  uint8_t index;
+  bool isLocal;
+} Upvalue;
+
+typedef enum {
+  TYPE_FUNCTION,
+  TYPE_INITIALIZER,
+  TYPE_METHOD,
+  TYPE_SCRIPT
+} FunctionType;
+
+typedef struct Compiler {
+  struct Compiler *enclosing;
+  ObjFunction *function;
+  FunctionType type;
+  Local locals[UINT8_COUNT];
+  int localCount;
+  Upvalue upvalues[UINT8_COUNT];
+  int scopeDepth;
+} Compiler;
+
+typedef struct TypeCompiler {
+  struct TypeCompiler *enclosing;
+} TypeCompiler;
+
 Parser parser;
-Chunk* compilingChunk;
+Compiler *current = NULL;
+TypeCompiler *currentType = NULL;
 
-static Chunk* currentChunk() {
-  return compilingChunk;
-}
+static Chunk *currentChunk() { return &current->function->chunk; }
 
-static void errorAt(Token* token, const char* message) {
-  if (parser.panicMode) return;
+static void errorAt(Token *token, const char *message) {
+  if (parser.panicMode)
+    return;
   parser.panicMode = true;
   fprintf(stderr, "[line %d] Error", token->line);
 
@@ -62,11 +96,9 @@ static void errorAt(Token* token, const char* message) {
   parser.hadError = true;
 }
 
-static void error(const char* message) {
-  errorAt(&parser.previous, message);
-}
+static void error(const char *message) { errorAt(&parser.previous, message); }
 
-static void errorAtCurrent(const char* message) {
+static void errorAtCurrent(const char *message) {
   errorAt(&parser.current, message);
 }
 
@@ -75,13 +107,14 @@ static void advance() {
 
   for (;;) {
     parser.current = scanToken();
-    if (parser.current.type != TOKEN_ERROR) break;
+    if (parser.current.type != TOKEN_ERROR)
+      break;
 
     errorAtCurrent(parser.current.start);
   }
 }
 
-static void consume(TokenType type, const char* message) {
+static void consume(TokenType type, const char *message) {
   if (parser.current.type == type) {
     advance();
     return;
@@ -90,6 +123,15 @@ static void consume(TokenType type, const char* message) {
   errorAtCurrent(message);
 }
 
+static bool check(TokenType type) { return parser.current.type == type; }
+
+static bool match(TokenType type) {
+  if (!check(type))
+    return false;
+  advance();
+  return true;
+}
+
 static void emitByte(uint8_t byte) {
   writeChunk(currentChunk(), byte, parser.previous.line);
 }
@@ -99,7 +141,31 @@ static void emitBytes(uint8_t byte1, uint8_t byte2) {
   emitByte(byte2);
 }
 
+static void emitLoop(int loopStart) {
+  emitByte(OP_LOOP);
+
+  int offset = currentChunk()->count - loopStart + 2;
+  if (offset > UINT16_MAX)
+    error("Loop body too large.");
+
+  emitByte((offset >> 8) & 0xff);
+  emitByte(offset & 0xff);
+}
+
+static int emitJump(uint8_t instruction) {
+  emitByte(instruction);
+  emitByte(0xff);
+  emitByte(0xff);
+  return currentChunk()->count - 2;
+}
+
 static void emitReturn() {
+  if (current->type == TYPE_INITIALIZER) {
+    emitBytes(OP_GET_LOCAL, 0);
+  } else {
+    emitByte(OP_NIL);
+  }
+
   emitByte(OP_RETURN);
 }
 
@@ -117,63 +183,628 @@ static void emitConstant(Value value) {
   emitBytes(OP_CONSTANT, makeConstant(value));
 }
 
-static void endCompiler() {
+static void patchJump(int offset) {
+  // -2 to adjust for the bytecode for the jump offset itself.
+  int jump = currentChunk()->count - offset - 2;
+
+  if (jump > UINT16_MAX) {
+    error("Too much code to jump over.");
+  }
+
+  currentChunk()->code[offset] = (jump >> 8) & 0xff;
+  currentChunk()->code[offset + 1] = jump & 0xff;
+}
+
+static void initCompiler(Compiler *compiler, FunctionType type) {
+  compiler->enclosing = current;
+  compiler->function = NULL;
+  compiler->type = type;
+  compiler->localCount = 0;
+  compiler->scopeDepth = 0;
+  compiler->function = newFunction();
+  current = compiler;
+  if (type != TYPE_SCRIPT) {
+    current->function->name =
+        copyString(parser.previous.start, parser.previous.length);
+  }
+
+  Local *local = &current->locals[current->localCount++];
+  local->depth = 0;
+  local->isCaptured = false;
+  if (type != TYPE_FUNCTION) {
+    local->name.start = "this";
+    local->name.length = 4;
+  } else {
+    local->name.start = "";
+    local->name.length = 0;
+  }
+}
+
+static ObjFunction *endCompiler() {
   emitReturn();
+  ObjFunction *function = current->function;
+
 #ifdef DEBUG_PRINT_CODE
   if (!parser.hadError) {
-    disassembleChunk(currentChunk(), "code");
+    disassembleChunk(currentChunk(), function->name != NULL
+                                         ? function->name->chars
+                                         : "<script>");
   }
 #endif
+
+  current = current->enclosing;
+  return function;
+}
+
+static void beginScope() { current->scopeDepth++; }
+
+static void endScope() {
+  current->scopeDepth--;
+
+  while (current->localCount > 0 &&
+         current->locals[current->localCount - 1].depth > current->scopeDepth) {
+    if (current->locals[current->localCount - 1].isCaptured) {
+      emitByte(OP_CLOSE_UPVALUE);
+    } else {
+      emitByte(OP_POP);
+    }
+    current->localCount--;
+  }
 }
 
 static void expression();
-static ParseRule* getRule(TokenType type);
+static void statement();
+static void declaration();
+static ParseRule *getRule(TokenType type);
 static void parsePrecedence(Precedence precedence);
+static void namedVariable(Token name, bool canAssign);
 
-static void expression() {
-  parsePrecedence(PREC_ASSIGNMENT);
+static void binary(bool canAssign) {
+  TokenType operatorType = parser.previous.type;
+  ParseRule *rule = getRule(operatorType);
+  parsePrecedence((Precedence)(rule->precedence + 1));
+
+  switch (operatorType) {
+  case TOKEN_BANG_EQUAL:
+    emitBytes(OP_EQUAL, OP_NOT);
+    break;
+  case TOKEN_EQUAL_EQUAL:
+    emitByte(OP_EQUAL);
+    break;
+  case TOKEN_GREATER:
+    emitByte(OP_GREATER);
+    break;
+  case TOKEN_GREATER_EQUAL:
+    emitBytes(OP_LESS, OP_NOT);
+    break;
+  case TOKEN_LESS:
+    emitByte(OP_LESS);
+    break;
+  case TOKEN_LESS_EQUAL:
+    emitBytes(OP_GREATER, OP_NOT);
+    break;
+  case TOKEN_PLUS:
+    emitByte(OP_ADD);
+    break;
+  case TOKEN_MINUS:
+    emitByte(OP_SUBTRACT);
+    break;
+  case TOKEN_STAR:
+    emitByte(OP_MULTIPLY);
+    break;
+  case TOKEN_SLASH:
+    emitByte(OP_DIVIDE);
+    break;
+  default:
+    return; // Unreachable.
+  }
 }
 
-static void grouping() {
+static uint8_t argumentList() {
+  uint8_t argCount = 0;
+  if (!check(TOKEN_RIGHT_PAREN)) {
+    do {
+      expression();
+      if (argCount == 255) {
+        error("Can't have more than 255 arguments.");
+      }
+      argCount++;
+    } while (match(TOKEN_COMMA));
+  }
+  consume(TOKEN_RIGHT_PAREN, "Expect ')' after arguments.");
+  return argCount;
+}
+
+static void call(bool canAssign) {
+  uint8_t argCount = argumentList();
+  emitBytes(OP_CALL, argCount);
+}
+
+static void literal(bool canAssign) {
+  switch (parser.previous.type) {
+  case TOKEN_FALSE:
+    emitByte(OP_FALSE);
+    break;
+  case TOKEN_NIL:
+    emitByte(OP_NIL);
+    break;
+  case TOKEN_TRUE:
+    emitByte(OP_TRUE);
+    break;
+  default:
+    return; // Unreachable.
+  }
+}
+
+static void expression() { parsePrecedence(PREC_ASSIGNMENT); }
+
+static void block() {
+  while (!check(TOKEN_RIGHT_BRACE) && !check(TOKEN_EOF)) {
+    declaration();
+  }
+
+  consume(TOKEN_RIGHT_BRACE, "Expect '}' after block.");
+}
+
+static uint8_t identifierConstant(Token *name) {
+  return makeConstant(OBJ_VAL(copyString(name->start, name->length)));
+}
+
+static bool identifiersEqual(Token *a, Token *b) {
+  if (a->length != b->length)
+    return false;
+  return memcmp(a->start, b->start, a->length) == 0;
+}
+
+static void dot(bool canAssign) {
+  consume(TOKEN_IDENTIFIER, "Expect property name after '.'.");
+  uint8_t name = identifierConstant(&parser.previous);
+
+  if (canAssign && match(TOKEN_EQUAL)) {
+    expression();
+    emitBytes(OP_SET_PROPERTY, name);
+  } else if (match(TOKEN_LEFT_PAREN)) {
+    uint8_t argCount = argumentList();
+    emitBytes(OP_INVOKE, name);
+    emitByte(argCount);
+  } else {
+    emitBytes(OP_GET_PROPERTY, name);
+  }
+}
+
+static int resolveLocal(Compiler *compiler, Token *name) {
+  for (int i = compiler->localCount - 1; i >= 0; i--) {
+    Local *local = &compiler->locals[i];
+    if (identifiersEqual(name, &local->name)) {
+      if (local->depth == -1) {
+        error("Can't read local variable in its own initializer.");
+      }
+      return i;
+    }
+  }
+
+  return -1;
+}
+
+static int addUpvalue(Compiler *compiler, uint8_t index, bool isLocal) {
+  int upvalueCount = compiler->function->upvalueCount;
+  for (int i = 0; i < upvalueCount; i++) {
+    Upvalue *upvalue = &compiler->upvalues[i];
+    if (upvalue->index == index && upvalue->isLocal == isLocal) {
+      return i;
+    }
+  }
+
+  if (upvalueCount == UINT8_COUNT) {
+    error("Too many closure variables in function.");
+    return 0;
+  }
+
+  compiler->upvalues[upvalueCount].isLocal = isLocal;
+  compiler->upvalues[upvalueCount].index = index;
+  return compiler->function->upvalueCount++;
+}
+
+static int resolveUpvalue(Compiler *compiler, Token *name) {
+  if (compiler->enclosing == NULL)
+    return -1;
+
+  int local = resolveLocal(compiler->enclosing, name);
+  if (local != -1) {
+    compiler->enclosing->locals[local].isCaptured = true;
+    return addUpvalue(compiler, (uint8_t)local, true);
+  }
+
+  int upvalue = resolveUpvalue(compiler->enclosing, name);
+  if (upvalue != -1) {
+    return addUpvalue(compiler, (uint8_t)upvalue, false);
+  }
+
+  return -1;
+}
+
+static void addLocal(Token name) {
+  if (current->localCount == UINT8_COUNT) {
+    error("Too many local variables in function.");
+    return;
+  }
+
+  Local *local = &current->locals[current->localCount++];
+  local->name = name;
+  local->depth = -1;
+  local->isCaptured = false;
+}
+
+static void declareVariable() {
+  if (current->scopeDepth == 0)
+    return;
+
+  Token *name = &parser.previous;
+  for (int i = current->localCount - 1; i >= 0; i--) {
+    Local *local = &current->locals[i];
+    if (local->depth != -1 && local->depth < current->scopeDepth) {
+      break;
+    }
+
+    if (identifiersEqual(name, &local->name)) {
+      error("Already a variable with this name in this scope.");
+    }
+  }
+  addLocal(*name);
+}
+
+static uint8_t parseVariable(const char *errorMessage) {
+  consume(TOKEN_IDENTIFIER, errorMessage);
+
+  declareVariable();
+  if (current->scopeDepth > 0)
+    return 0;
+
+  return identifierConstant(&parser.previous);
+}
+
+static void markInitialized() {
+  if (current->scopeDepth == 0)
+    return;
+  current->locals[current->localCount - 1].depth = current->scopeDepth;
+}
+
+static void defineVariable(uint8_t global) {
+  if (current->scopeDepth > 0) {
+    markInitialized();
+    return;
+  }
+
+  emitBytes(OP_DEFINE_GLOBAL, global);
+}
+
+static void function(FunctionType type) {
+  Compiler compiler;
+  initCompiler(&compiler, type);
+  beginScope();
+
+  consume(TOKEN_LEFT_PAREN, "Expect '(' after function name.");
+  if (!check(TOKEN_RIGHT_PAREN)) {
+    do {
+      current->function->arity++;
+      if (current->function->arity > 255) {
+        errorAtCurrent("Can't have more than 255 parameters.");
+      }
+      uint8_t constant = parseVariable("Expect parameter name.");
+      defineVariable(constant);
+    } while (match(TOKEN_COMMA));
+  }
+  consume(TOKEN_RIGHT_PAREN, "Expect ')' after parameters.");
+  consume(TOKEN_LEFT_BRACE, "Expect '{' before function body.");
+  block();
+
+  ObjFunction *function = endCompiler();
+  emitBytes(OP_CLOSURE, makeConstant(OBJ_VAL(function)));
+
+  for (int i = 0; i < function->upvalueCount; i++) {
+    emitByte(compiler.upvalues[i].isLocal ? 1 : 0);
+    emitByte(compiler.upvalues[i].index);
+  }
+}
+
+static void method() {
+  consume(TOKEN_IDENTIFIER, "Expect method name.");
+  uint8_t constant = identifierConstant(&parser.previous);
+
+  FunctionType type = TYPE_METHOD;
+  if (parser.previous.length == 4 &&
+      memcmp(parser.previous.start, "init", 4) == 0) {
+    type = TYPE_INITIALIZER;
+  }
+
+  function(type);
+  emitBytes(OP_METHOD, constant);
+}
+
+static void typeDeclaration() {
+  consume(TOKEN_IDENTIFIER, "Expect type name.");
+  Token typeName = parser.previous;
+  uint8_t nameConstant = identifierConstant(&parser.previous);
+  declareVariable();
+
+  emitBytes(OP_TYPE, nameConstant);
+  defineVariable(nameConstant);
+
+  TypeCompiler typeCompiler;
+  typeCompiler.enclosing = currentType;
+  currentType = &typeCompiler;
+
+  namedVariable(typeName, false);
+  consume(TOKEN_LEFT_BRACE, "Expect '{' before type body.");
+  while (!check(TOKEN_RIGHT_BRACE) && !check(TOKEN_EOF)) {
+    method();
+  }
+  consume(TOKEN_RIGHT_BRACE, "Expect '}' after type body.");
+  emitByte(OP_POP);
+
+  currentType = currentType->enclosing;
+}
+
+static void funDeclaration() {
+  uint8_t global = parseVariable("Expect function name.");
+  markInitialized();
+  function(TYPE_FUNCTION);
+  defineVariable(global);
+}
+
+static void and_(bool canAssign) {
+  int endJump = emitJump(OP_JUMP_IF_FALSE);
+
+  emitByte(OP_POP);
+  parsePrecedence(PREC_AND);
+
+  patchJump(endJump);
+}
+
+static void varDeclaration() {
+  uint8_t global = parseVariable("Expect variable name.");
+
+  if (match(TOKEN_EQUAL)) {
+    expression();
+  } else {
+    emitByte(OP_NIL);
+  }
+  consume(TOKEN_SEMICOLON, "Expect ';' after variable declaration.");
+
+  defineVariable(global);
+}
+
+static void expressionStatement() {
+  expression();
+  consume(TOKEN_SEMICOLON, "Expect ';' after expression.");
+  emitByte(OP_POP);
+}
+
+static void forStatement() {
+  beginScope();
+  consume(TOKEN_LEFT_PAREN, "Expect '(' after 'for'.");
+  if (match(TOKEN_SEMICOLON)) {
+    // No initializer.
+  } else if (match(TOKEN_LET)) {
+    varDeclaration();
+  } else {
+    expressionStatement();
+  }
+
+  int loopStart = currentChunk()->count;
+  int exitJump = -1;
+  if (!match(TOKEN_SEMICOLON)) {
+    expression();
+    consume(TOKEN_SEMICOLON, "Expect ';' after loop condition.");
+
+    // Jump out of the loop if the condition is false.
+    exitJump = emitJump(OP_JUMP_IF_FALSE);
+    emitByte(OP_POP); // Condition.
+  }
+
+  if (!match(TOKEN_RIGHT_PAREN)) {
+    int bodyJump = emitJump(OP_JUMP);
+    int incrementStart = currentChunk()->count;
+    expression();
+    emitByte(OP_POP);
+    consume(TOKEN_RIGHT_PAREN, "Expect ')' after for clauses.");
+
+    emitLoop(loopStart);
+    loopStart = incrementStart;
+    patchJump(bodyJump);
+  }
+
+  statement();
+  emitLoop(loopStart);
+
+  if (exitJump != -1) {
+    patchJump(exitJump);
+    emitByte(OP_POP); // Condition.
+  }
+
+  endScope();
+}
+
+static void ifStatement() {
+  consume(TOKEN_LEFT_PAREN, "Expect '(' after 'if'.");
+  expression();
+  consume(TOKEN_RIGHT_PAREN, "Expect ')' after condition.");
+
+  int thenJump = emitJump(OP_JUMP_IF_FALSE);
+  emitByte(OP_POP);
+  statement();
+
+  int elseJump = emitJump(OP_JUMP);
+
+  patchJump(thenJump);
+  emitByte(OP_POP);
+
+  if (match(TOKEN_ELSE))
+    statement();
+  patchJump(elseJump);
+}
+
+static void printStatement() {
+  expression();
+  consume(TOKEN_SEMICOLON, "Expect ';' after value.");
+  emitByte(OP_PRINT);
+}
+
+static void returnStatement() {
+  if (current->type == TYPE_SCRIPT) {
+    error("Can't return from top-level code.");
+  }
+
+  if (match(TOKEN_SEMICOLON)) {
+    emitReturn();
+  } else {
+    if (current->type == TYPE_INITIALIZER) {
+      error("Can't return a value from an initializer.");
+    }
+
+    expression();
+    consume(TOKEN_SEMICOLON, "Expect ';' after return value.");
+    emitByte(OP_RETURN);
+  }
+}
+
+static void whileStatement() {
+  int loopStart = currentChunk()->count;
+  consume(TOKEN_LEFT_PAREN, "Expect '(' after 'while'.");
+  expression();
+  consume(TOKEN_RIGHT_PAREN, "Expect ')' after condition.");
+
+  int exitJump = emitJump(OP_JUMP_IF_FALSE);
+  emitByte(OP_POP);
+  statement();
+  emitLoop(loopStart);
+
+  patchJump(exitJump);
+  emitByte(OP_POP);
+}
+
+static void synchronize() {
+  parser.panicMode = false;
+
+  while (parser.current.type != TOKEN_EOF) {
+    if (parser.previous.type == TOKEN_SEMICOLON)
+      return;
+    switch (parser.current.type) {
+    case TOKEN_TYPE:
+    case TOKEN_FN:
+    case TOKEN_LET:
+    case TOKEN_FOR:
+    case TOKEN_IF:
+    case TOKEN_WHILE:
+    case TOKEN_PRINT:
+    case TOKEN_RETURN:
+      return;
+
+    default:; // Do nothing.
+    }
+
+    advance();
+  }
+}
+
+static void declaration() {
+  if (match(TOKEN_TYPE)) {
+    typeDeclaration();
+  } else if (match(TOKEN_FN)) {
+    funDeclaration();
+  } else if (match(TOKEN_LET)) {
+    varDeclaration();
+  } else {
+    statement();
+  }
+
+  if (parser.panicMode)
+    synchronize();
+}
+
+static void statement() {
+  if (match(TOKEN_PRINT)) {
+    printStatement();
+  } else if (match(TOKEN_FOR)) {
+    forStatement();
+  } else if (match(TOKEN_IF)) {
+    ifStatement();
+  } else if (match(TOKEN_RETURN)) {
+    returnStatement();
+  } else if (match(TOKEN_WHILE)) {
+    whileStatement();
+  } else if (match(TOKEN_LEFT_BRACE)) {
+    beginScope();
+    block();
+    endScope();
+  } else {
+    expressionStatement();
+  }
+}
+
+static void grouping(bool canAssign) {
   expression();
   consume(TOKEN_RIGHT_PAREN, "Expect ')' after expression.");
 }
 
-static void number() {
+static void number(bool canAssign) {
   double value = strtod(parser.previous.start, NULL);
   emitConstant(NUMBER_VAL(value));
 }
 
-static void binary() {
-  TokenType operatorType = parser.previous.type;
-  ParseRule* rule = getRule(operatorType);
-  parsePrecedence((Precedence)(rule->precedence + 1));
+static void or_(bool canAssign) {
+  int elseJump = emitJump(OP_JUMP_IF_FALSE);
+  int endJump = emitJump(OP_JUMP);
 
-  switch (operatorType) {
-    case TOKEN_BANG_EQUAL:    emitBytes(OP_EQUAL, OP_NOT); break;
-    case TOKEN_EQUAL_EQUAL:   emitByte(OP_EQUAL); break;
-    case TOKEN_GREATER:       emitByte(OP_GREATER); break;
-    case TOKEN_GREATER_EQUAL: emitBytes(OP_LESS, OP_NOT); break;
-    case TOKEN_LESS:          emitByte(OP_LESS); break;
-    case TOKEN_LESS_EQUAL:    emitBytes(OP_GREATER, OP_NOT); break;
-    case TOKEN_PLUS:          emitByte(OP_ADD); break;
-    case TOKEN_MINUS:         emitByte(OP_SUBTRACT); break;
-    case TOKEN_STAR:          emitByte(OP_MULTIPLY); break;
-    case TOKEN_SLASH:         emitByte(OP_DIVIDE); break;
-    default: return; // Unreachable.
+  patchJump(elseJump);
+  emitByte(OP_POP);
+
+  parsePrecedence(PREC_OR);
+  patchJump(endJump);
+}
+
+static void string(bool canAssign) {
+  emitConstant(OBJ_VAL(
+      copyString(parser.previous.start + 1, parser.previous.length - 2)));
+}
+
+static void namedVariable(Token name, bool canAssign) {
+  uint8_t getOp, setOp;
+  int arg = resolveLocal(current, &name);
+  if (arg != -1) {
+    getOp = OP_GET_LOCAL;
+    setOp = OP_SET_LOCAL;
+  } else if ((arg = resolveUpvalue(current, &name)) != -1) {
+    getOp = OP_GET_UPVALUE;
+    setOp = OP_SET_UPVALUE;
+  } else {
+    arg = identifierConstant(&name);
+    getOp = OP_GET_GLOBAL;
+    setOp = OP_SET_GLOBAL;
+  }
+
+  if (canAssign && match(TOKEN_EQUAL)) {
+    expression();
+    emitBytes(setOp, (uint8_t)arg);
+  } else {
+    emitBytes(getOp, (uint8_t)arg);
   }
 }
 
-static void literal() {
-  switch (parser.previous.type) {
-    case TOKEN_FALSE: emitByte(OP_FALSE); break;
-    case TOKEN_NIL: emitByte(OP_NIL); break;
-    case TOKEN_TRUE: emitByte(OP_TRUE); break;
-    default: return; // Unreachable.
-  }
+static void variable(bool canAssign) {
+  namedVariable(parser.previous, canAssign);
 }
 
-static void unary() {
+static void this_(bool canAssign) {
+  if (currentType == NULL) {
+    error("Can't use 'this' outside of a type.");
+    return;
+  }
+
+  variable(false);
+}
+
+static void unary(bool canAssign) {
   TokenType operatorType = parser.previous.type;
 
   // Compile the operand.
@@ -181,59 +812,60 @@ static void unary() {
 
   // Emit the operator instruction.
   switch (operatorType) {
-    case TOKEN_BANG: emitByte(OP_NOT); break;
-    case TOKEN_MINUS: emitByte(OP_NEGATE); break;
-    default: return; // Unreachable.
+  case TOKEN_MINUS:
+    emitByte(OP_NEGATE);
+    break;
+  case TOKEN_BANG:
+    emitByte(OP_NOT);
+    break;
+  default:
+    return; // Unreachable.
   }
 }
 
 ParseRule rules[] = {
-  [TOKEN_LEFT_PAREN]    = {grouping, NULL,   PREC_NONE},
-  [TOKEN_RIGHT_PAREN]   = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_LEFT_BRACE]    = {NULL,     NULL,   PREC_NONE}, 
-  [TOKEN_RIGHT_BRACE]   = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_COMMA]         = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_DOT]           = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_MINUS]         = {unary,    binary, PREC_TERM},
-  [TOKEN_PLUS]          = {NULL,     binary, PREC_TERM},
-  [TOKEN_SEMICOLON]     = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_SLASH]         = {NULL,     binary, PREC_FACTOR},
-  [TOKEN_STAR]          = {NULL,     binary, PREC_FACTOR},
-  [TOKEN_BANG]          = {unary,    NULL,   PREC_NONE},
-  [TOKEN_BANG_EQUAL]    = {NULL,     binary, PREC_EQUALITY},
-  [TOKEN_EQUAL]         = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_EQUAL_EQUAL]   = {NULL,     binary, PREC_EQUALITY},
-  [TOKEN_GREATER]       = {NULL,     binary, PREC_COMPARISON},
-  [TOKEN_GREATER_EQUAL] = {NULL,     binary, PREC_COMPARISON},
-  [TOKEN_LESS]          = {NULL,     binary, PREC_COMPARISON},
-  [TOKEN_LESS_EQUAL]    = {NULL,     binary, PREC_COMPARISON},
-  [TOKEN_IDENTIFIER]    = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_STRING]        = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_NUMBER]        = {number,   NULL,   PREC_NONE},
-  [TOKEN_AND]           = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_TYPE]          = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_ELSE]          = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_FALSE]         = {literal,  NULL,   PREC_NONE},
-  [TOKEN_FOR]           = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_FN]            = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_IF]            = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_NIL]           = {literal,  NULL,   PREC_NONE},
-  [TOKEN_OR]            = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_PRINT]         = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_RETURN]        = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_SUPER]         = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_THIS]          = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_TRUE]          = {literal,  NULL,   PREC_NONE},
-  [TOKEN_LET]           = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_WHILE]         = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_ERROR]         = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_EOF]           = {NULL,     NULL,   PREC_NONE},
+    [TOKEN_LEFT_PAREN] = {grouping, call, PREC_CALL},
+    [TOKEN_RIGHT_PAREN] = {NULL, NULL, PREC_NONE},
+    [TOKEN_LEFT_BRACE] = {NULL, NULL, PREC_NONE},
+    [TOKEN_RIGHT_BRACE] = {NULL, NULL, PREC_NONE},
+    [TOKEN_COMMA] = {NULL, NULL, PREC_NONE},
+    [TOKEN_DOT] = {NULL, dot, PREC_CALL},
+    [TOKEN_MINUS] = {unary, binary, PREC_TERM},
+    [TOKEN_PLUS] = {NULL, binary, PREC_TERM},
+    [TOKEN_SEMICOLON] = {NULL, NULL, PREC_NONE},
+    [TOKEN_SLASH] = {NULL, binary, PREC_FACTOR},
+    [TOKEN_STAR] = {NULL, binary, PREC_FACTOR},
+    [TOKEN_BANG] = {unary, NULL, PREC_NONE},
+    [TOKEN_BANG_EQUAL] = {NULL, binary, PREC_EQUALITY},
+    [TOKEN_EQUAL] = {NULL, NULL, PREC_NONE},
+    [TOKEN_EQUAL_EQUAL] = {NULL, binary, PREC_EQUALITY},
+    [TOKEN_GREATER] = {NULL, binary, PREC_COMPARISON},
+    [TOKEN_GREATER_EQUAL] = {NULL, binary, PREC_COMPARISON},
+    [TOKEN_LESS] = {NULL, binary, PREC_COMPARISON},
+    [TOKEN_LESS_EQUAL] = {NULL, binary, PREC_COMPARISON},
+    [TOKEN_IDENTIFIER] = {variable, NULL, PREC_NONE},
+    [TOKEN_STRING] = {string, NULL, PREC_NONE},
+    [TOKEN_NUMBER] = {number, NULL, PREC_NONE},
+    [TOKEN_AND] = {NULL, and_, PREC_AND},
+    [TOKEN_TYPE] = {NULL, NULL, PREC_NONE},
+    [TOKEN_ELSE] = {NULL, NULL, PREC_NONE},
+    [TOKEN_FALSE] = {literal, NULL, PREC_NONE},
+    [TOKEN_FOR] = {NULL, NULL, PREC_NONE},
+    [TOKEN_FN] = {NULL, NULL, PREC_NONE},
+    [TOKEN_IF] = {NULL, NULL, PREC_NONE},
+    [TOKEN_NIL] = {literal, NULL, PREC_NONE},
+    [TOKEN_OR] = {NULL, or_, PREC_OR},
+    [TOKEN_PRINT] = {NULL, NULL, PREC_NONE},
+    [TOKEN_RETURN] = {NULL, NULL, PREC_NONE},
+    [TOKEN_SUPER] = {NULL, NULL, PREC_NONE},
+    [TOKEN_THIS] = {this_, NULL, PREC_NONE},
+    [TOKEN_TRUE] = {literal, NULL, PREC_NONE},
+    [TOKEN_LET] = {NULL, NULL, PREC_NONE},
+    [TOKEN_WHILE] = {NULL, NULL, PREC_NONE},
+    [TOKEN_ERROR] = {NULL, NULL, PREC_NONE},
+    [TOKEN_EOF] = {NULL, NULL, PREC_NONE},
 };
 
-static ParseRule* getRule(TokenType type) {
-  return &rules[type];
-}
-
 static void parsePrecedence(Precedence precedence) {
   advance();
   ParseFn prefixRule = getRule(parser.previous.type)->prefix;
@@ -242,25 +874,44 @@ static void parsePrecedence(Precedence precedence) {
     return;
   }
 
-  prefixRule();
+  bool canAssign = precedence <= PREC_ASSIGNMENT;
+  prefixRule(canAssign);
 
   while (precedence <= getRule(parser.current.type)->precedence) {
     advance();
     ParseFn infixRule = getRule(parser.previous.type)->infix;
-    infixRule();
+    infixRule(canAssign);
+  }
+
+  if (canAssign && match(TOKEN_EQUAL)) {
+    error("Invalid assignment target.");
   }
 }
 
-bool compile(const char* source, Chunk* chunk) {
-  newScanner(source);
-  compilingChunk = chunk;
+static ParseRule *getRule(TokenType type) { return &rules[type]; }
+
+ObjFunction *compile(const char *source) {
+  initScanner(source);
+  Compiler compiler;
+  initCompiler(&compiler, TYPE_SCRIPT);
 
   parser.hadError = false;
   parser.panicMode = false;
 
   advance();
-  expression();
-  consume(TOKEN_EOF, "Expect end of expression.");
-  endCompiler();
-  return !parser.hadError;
+
+  while (!match(TOKEN_EOF)) {
+    declaration();
+  }
+
+  ObjFunction *function = endCompiler();
+  return parser.hadError ? NULL : function;
+}
+
+void markCompilerRoots() {
+  Compiler *compiler = current;
+  while (compiler != NULL) {
+    markObject((Obj *)compiler->function);
+    compiler = compiler->enclosing;
+  }
 }
diff --git a/src/compiler.h b/src/compiler.h
index 67eb4d0..1266694 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -1,9 +1,11 @@
-#ifndef ztl_compiler_h
-#define ztl_compiler_h
+#ifndef zlc_compiler_h
+#define zlc_compiler_h
 
 #include "vm.h"
+#include "object.h"
 
-bool compile(const char* source, Chunk* chunk);
+ObjFunction* compile(const char* source);
+void markCompilerRoots();
 
 #endif
 
diff --git a/src/debug.c b/src/debug.c
index dca5802..6a97c53 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -1,9 +1,10 @@
 #include <stdio.h>
 
 #include "debug.h"
+#include "object.h"
 #include "value.h"
 
-void disassembleChunk(Chunk* chunk, const char* name) {
+void disassembleChunk(Chunk *chunk, const char *name) {
   printf("== %s ==\n", name);
 
   for (int offset = 0; offset < chunk->count;) {
@@ -11,8 +12,7 @@ void disassembleChunk(Chunk* chunk, const char* name) {
   }
 }
 
-static int constantInstruction(const char* name, Chunk* chunk,
-                               int offset) {
+static int constantInstruction(const char *name, Chunk *chunk, int offset) {
   uint8_t constant = chunk->code[offset + 1];
   printf("%-16s %4d '", name, constant);
   printValue(chunk->constants.values[constant]);
@@ -20,15 +20,37 @@ static int constantInstruction(const char* name, Chunk* chunk,
   return offset + 2;
 }
 
-static int simpleInstruction(const char* name, int offset) {
+static int invokeInstruction(const char *name, Chunk *chunk, int offset) {
+  uint8_t constant = chunk->code[offset + 1];
+  uint8_t argCount = chunk->code[offset + 2];
+  printf("%-16s (%d args) %4d '", name, argCount, constant);
+  printValue(chunk->constants.values[constant]);
+  printf("'\n");
+  return offset + 3;
+}
+
+static int simpleInstruction(const char *name, int offset) {
   printf("%s\n", name);
   return offset + 1;
 }
 
-int disassembleInstruction(Chunk* chunk, int offset) {
+static int byteInstruction(const char *name, Chunk *chunk, int offset) {
+  uint8_t slot = chunk->code[offset + 1];
+  printf("%-16s %4d\n", name, slot);
+  return offset + 2;
+}
+
+static int jumpInstruction(const char *name, int sign, Chunk *chunk,
+                           int offset) {
+  uint16_t jump = (uint16_t)(chunk->code[offset + 1] << 8);
+  jump |= chunk->code[offset + 2];
+  printf("%-16s %4d -> %d\n", name, offset, offset + 3 + sign * jump);
+  return offset + 3;
+}
+
+int disassembleInstruction(Chunk *chunk, int offset) {
   printf("%04d ", offset);
-  if (offset > 0 &&
-      chunk->lines[offset] == chunk->lines[offset - 1]) {
+  if (offset > 0 && chunk->lines[offset] == chunk->lines[offset - 1]) {
     printf("   | ");
   } else {
     printf("%4d ", chunk->lines[offset]);
@@ -36,38 +58,91 @@ int disassembleInstruction(Chunk* chunk, int offset) {
 
   uint8_t instruction = chunk->code[offset];
   switch (instruction) {
-    case OP_NOOP:
-      return simpleInstruction("OP_NOOP", offset);
-    case OP_NEGATE:
-      return simpleInstruction("OP_NEGATE", offset);     
-    case OP_CONSTANT:
-      return constantInstruction("OP_CONSTANT", chunk, offset);
-    case OP_NIL:
-      return simpleInstruction("OP_NIL", offset);
-    case OP_TRUE:
-      return simpleInstruction("OP_TRUE", offset);
-    case OP_FALSE:
-      return simpleInstruction("OP_FALSE", offset);
-    case OP_EQUAL:
-      return simpleInstruction("OP_EQUAL", offset);
-    case OP_GREATER:
-      return simpleInstruction("OP_GREATER", offset);
-    case OP_LESS:
-      return simpleInstruction("OP_LESS", offset);
-    case OP_ADD:
-      return simpleInstruction("OP_ADD", offset);
-    case OP_SUBTRACT:
-      return simpleInstruction("OP_SUBTRACT", offset);
-    case OP_MULTIPLY:
-      return simpleInstruction("OP_MULTIPLY", offset);
-    case OP_DIVIDE:
-      return simpleInstruction("OP_DIVIDE", offset);
-    case OP_NOT:
-      return simpleInstruction("OP_NOT", offset);
-    case OP_RETURN:
-      return simpleInstruction("OP_RETURN", offset);
-    default:
-      printf("Unknown opcode %d\n", instruction);
-      return offset + 1;
+  case OP_CONSTANT:
+    return constantInstruction("OP_CONSTANT", chunk, offset);
+  case OP_NIL:
+    return simpleInstruction("OP_NIL", offset);
+  case OP_TRUE:
+    return simpleInstruction("OP_TRUE", offset);
+  case OP_FALSE:
+    return simpleInstruction("OP_FALSE", offset);
+  case OP_SET_GLOBAL:
+    return constantInstruction("OP_SET_GLOBAL", chunk, offset);
+  case OP_EQUAL:
+    return simpleInstruction("OP_EQUAL", offset);
+  case OP_GET_PROPERTY:
+    return constantInstruction("OP_GET_PROPERTY", chunk, offset);
+  case OP_SET_PROPERTY:
+    return constantInstruction("OP_SET_PROPERTY", chunk, offset);
+  case OP_GET_UPVALUE:
+    return byteInstruction("OP_GET_UPVALUE", chunk, offset);
+  case OP_SET_UPVALUE:
+    return byteInstruction("OP_SET_UPVALUE", chunk, offset);
+  case OP_POP:
+    return simpleInstruction("OP_POP", offset);
+  case OP_GET_LOCAL:
+    return byteInstruction("OP_GET_LOCAL", chunk, offset);
+  case OP_SET_LOCAL:
+    return byteInstruction("OP_SET_LOCAL", chunk, offset);
+  case OP_GET_GLOBAL:
+    return constantInstruction("OP_GET_GLOBAL", chunk, offset);
+  case OP_DEFINE_GLOBAL:
+    return constantInstruction("OP_DEFINE_GLOBAL", chunk, offset);
+  case OP_GREATER:
+    return simpleInstruction("OP_GREATER", offset);
+  case OP_LESS:
+    return simpleInstruction("OP_LESS", offset);
+  case OP_ADD:
+    return simpleInstruction("OP_ADD", offset);
+  case OP_SUBTRACT:
+    return simpleInstruction("OP_SUBTRACT", offset);
+  case OP_MULTIPLY:
+    return simpleInstruction("OP_MULTIPLY", offset);
+  case OP_DIVIDE:
+    return simpleInstruction("OP_DIVIDE", offset);
+  case OP_NOT:
+    return simpleInstruction("OP_NOT", offset);
+  case OP_NEGATE:
+    return simpleInstruction("OP_NEGATE", offset);
+  case OP_PRINT:
+    return simpleInstruction("OP_PRINT", offset);
+  case OP_JUMP:
+    return jumpInstruction("OP_JUMP", 1, chunk, offset);
+  case OP_JUMP_IF_FALSE:
+    return jumpInstruction("OP_JUMP_IF_FALSE", 1, chunk, offset);
+  case OP_LOOP:
+    return jumpInstruction("OP_LOOP", -1, chunk, offset);
+  case OP_CALL:
+    return byteInstruction("OP_CALL", chunk, offset);
+  case OP_INVOKE:
+    return invokeInstruction("OP_INVOKE", chunk, offset);
+  case OP_CLOSURE: {
+    offset++;
+    uint8_t constant = chunk->code[offset++];
+    printf("%-16s %4d ", "OP_CLOSURE", constant);
+    printValue(chunk->constants.values[constant]);
+    printf("\n");
+
+    ObjFunction *function = AS_FUNCTION(chunk->constants.values[constant]);
+    for (int j = 0; j < function->upvalueCount; j++) {
+      int isLocal = chunk->code[offset++];
+      int index = chunk->code[offset++];
+      printf("%04d      |                     %s %d\n", offset - 2,
+             isLocal ? "local" : "upvalue", index);
+    }
+
+    return offset;
+  }
+  case OP_CLOSE_UPVALUE:
+    return simpleInstruction("OP_CLOSE_UPVALUE", offset);
+  case OP_RETURN:
+    return simpleInstruction("OP_RETURN", offset);
+  case OP_TYPE:
+    return constantInstruction("OP_TYPE", chunk, offset);
+  case OP_METHOD:
+    return constantInstruction("OP_METHOD", chunk, offset);
+  default:
+    printf("Unknown opcode %d\n", instruction);
+    return offset + 1;
   }
 }
diff --git a/src/debug.h b/src/debug.h
index 0495cda..7ab8aed 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -1,5 +1,5 @@
-#ifndef ztl_debug_h
-#define ztl_debug_h
+#ifndef zlc_debug_h
+#define zlc_debug_h
 
 #include "chunk.h"
 
diff --git a/src/main.c b/src/main.c
index 5f73ee6..ece5fd6 100644
--- a/src/main.c
+++ b/src/main.c
@@ -7,6 +7,7 @@
 #include "debug.h"
 #include "vm.h"
 
+
 static void repl() {
   char line[1024];
   for (;;) {
@@ -21,8 +22,8 @@ static void repl() {
   }
 }
 
-static char *readFile(const char *path) {
-  FILE *file = fopen(path, "rb");
+static char* readFile(const char* path) {
+  FILE* file = fopen(path, "rb");
   if (file == NULL) {
     fprintf(stderr, "Could not open file \"%s\".\n", path);
     exit(74);
@@ -32,12 +33,11 @@ static char *readFile(const char *path) {
   size_t fileSize = ftell(file);
   rewind(file);
 
-  char *buffer = (char*)malloc(fileSize + 1);
+  char* buffer = (char*)malloc(fileSize + 1);
   if (buffer == NULL) {
     fprintf(stderr, "Not enough memory to read \"%s\".\n", path);
     exit(74);
   }
-
   size_t bytesRead = fread(buffer, sizeof(char), fileSize, file);
   if (bytesRead < fileSize) {
     fprintf(stderr, "Could not read file \"%s\".\n", path);
@@ -50,8 +50,8 @@ static char *readFile(const char *path) {
   return buffer;
 }
 
-static void runFile(const char *path) {
-  char *source = readFile(path);
+static void runFile(const char* path) {
+  char* source = readFile(path);
   InterpretResult result = interpret(source);
   free(source); 
 
@@ -59,15 +59,15 @@ static void runFile(const char *path) {
   if (result == INTERPRET_RUNTIME_ERROR) exit(70);
 }
 
-int main(int argc, const char* *argv) {
-  newVM();
-  
+int main(int argc, const char* argv[]) {
+  initVM();
+
   if (argc == 1) {
     repl();
   } else if (argc == 2) {
     runFile(argv[1]);
   } else {
-    fprintf(stderr, "Usage: clox [path]\n");
+    fprintf(stderr, "Usage: zlc [path]\n");
     exit(64);
   }
 
diff --git a/src/memory.c b/src/memory.c
index 3a928d4..71e15d9 100644
--- a/src/memory.c
+++ b/src/memory.c
@@ -1,16 +1,247 @@
 #include <stdlib.h>
 
-#include "chunk.h"
+#include "compiler.h"
 #include "memory.h"
+#include "vm.h"
+
+#ifdef DEBUG_LOG_GC
+#include "debug.h"
+#include <stdio.h>
+#endif
+
+#define GC_HEAP_GROW_FACTOR 2
+
+void *reallocate(void *pointer, size_t oldSize, size_t newSize) {
+  vm.bytesAllocated += newSize - oldSize;
+  if (newSize > oldSize) {
+#ifdef DEBUG_STRESS_GC
+    collectGarbage();
+#endif
+
+    if (vm.bytesAllocated > vm.nextGC) {
+      collectGarbage();
+    }
+  }
 
-void* reallocate(void *pointer, size_t oldSize, size_t newSize) {
   if (newSize == 0) {
     free(pointer);
     return NULL;
   }
 
   void *result = realloc(pointer, newSize);
-  if (result == NULL) exit(1);
+  if (result == NULL)
+    exit(1);
   return result;
 }
 
+void markObject(Obj *object) {
+  if (object == NULL)
+    return;
+  if (object->isMarked)
+    return;
+#ifdef DEBUG_LOG_GC
+  printf("%p mark ", (void *)object);
+  printValue(OBJ_VAL(object));
+  printf("\n");
+#endif
+
+  object->isMarked = true;
+
+  if (vm.grayCapacity < vm.grayCount + 1) {
+    vm.grayCapacity = GROW_CAPACITY(vm.grayCapacity);
+    vm.grayStack =
+        (Obj **)realloc(vm.grayStack, sizeof(Obj *) * vm.grayCapacity);
+
+    if (vm.grayStack == NULL)
+      exit(1);
+  }
+
+  vm.grayStack[vm.grayCount++] = object;
+}
+
+void markValue(Value value) {
+  if (IS_OBJ(value))
+    markObject(AS_OBJ(value));
+}
+
+static void markArray(ValueArray *array) {
+  for (int i = 0; i < array->count; i++) {
+    markValue(array->values[i]);
+  }
+}
+
+static void blackenObject(Obj *object) {
+#ifdef DEBUG_LOG_GC
+  printf("%p blacken ", (void *)object);
+  printValue(OBJ_VAL(object));
+  printf("\n");
+#endif
+
+  switch (object->type) {
+  case OBJ_BOUND_METHOD: {
+    ObjBoundMethod *bound = (ObjBoundMethod *)object;
+    markValue(bound->receiver);
+    markObject((Obj *)bound->method);
+    break;
+  }
+  case OBJ_TYPE: {
+    TypeObj *t = (TypeObj *)object;
+    markObject((Obj *)t->name);
+    markTable(&t->methods);
+    break;
+  }
+  case OBJ_CLOSURE: {
+    ObjClosure *closure = (ObjClosure *)object;
+    markObject((Obj *)closure->function);
+    for (int i = 0; i < closure->upvalueCount; i++) {
+      markObject((Obj *)closure->upvalues[i]);
+    }
+    break;
+  }
+  case OBJ_FUNCTION: {
+    ObjFunction *function = (ObjFunction *)object;
+    markObject((Obj *)function->name);
+    markArray(&function->chunk.constants);
+    break;
+  }
+  case OBJ_INSTANCE: {
+    ObjInstance *instance = (ObjInstance *)object;
+    markObject((Obj *)instance->t);
+    markTable(&instance->fields);
+    break;
+  }
+  case OBJ_UPVALUE:
+    markValue(((ObjUpvalue *)object)->closed);
+    break;
+  case OBJ_NATIVE:
+  case OBJ_STRING:
+    break;
+  }
+}
+
+static void freeObject(Obj *object) {
+  switch (object->type) {
+  case OBJ_BOUND_METHOD:
+    FREE(ObjBoundMethod, object);
+    break;
+  case OBJ_TYPE: {
+    TypeObj *t = (TypeObj *)object;
+    freeTable(&t->methods);
+    FREE(TypeObj, object);
+    break;
+  }
+  case OBJ_CLOSURE: {
+    ObjClosure *closure = (ObjClosure *)object;
+    FREE_ARRAY(ObjUpvalue *, closure->upvalues, closure->upvalueCount);
+    FREE(ObjClosure, object);
+    break;
+  }
+  case OBJ_FUNCTION: {
+    ObjFunction *function = (ObjFunction *)object;
+    freeChunk(&function->chunk);
+    FREE(ObjFunction, object);
+    break;
+  }
+  case OBJ_INSTANCE: {
+    ObjInstance *instance = (ObjInstance *)object;
+    freeTable(&instance->fields);
+    FREE(ObjInstance, object);
+    break;
+  }
+  case OBJ_NATIVE:
+    FREE(ObjNative, object);
+    break;
+  case OBJ_STRING: {
+    ObjString *string = (ObjString *)object;
+    FREE_ARRAY(char, string->chars, string->length + 1);
+    FREE(ObjString, object);
+    break;
+  }
+  case OBJ_UPVALUE: {
+    FREE(ObjUpvalue, object);
+    break;
+  }
+  }
+}
+
+void freeObjects() {
+  Obj *object = vm.objects;
+  while (object != NULL) {
+#ifdef DEBUG_LOG_GC
+    printf("%p free type %d\n", (void *)object, object->type);
+#endif
+    Obj *next = object->next;
+    freeObject(object);
+    object = next;
+  }
+
+  free(vm.grayStack);
+}
+
+static void markRoots() {
+  for (Value *slot = vm.stack; slot < vm.stackTop; slot++) {
+    markValue(*slot);
+  }
+
+  for (int i = 0; i < vm.frameCount; i++) {
+    markObject((Obj *)vm.frames[i].closure);
+  }
+
+  for (ObjUpvalue *upvalue = vm.openUpvalues; upvalue != NULL;
+       upvalue = upvalue->next) {
+    markObject((Obj *)upvalue);
+  }
+
+  markTable(&vm.globals);
+  markCompilerRoots();
+  markObject((Obj *)vm.initString);
+}
+
+static void traceReferences() {
+  while (vm.grayCount > 0) {
+    Obj *object = vm.grayStack[--vm.grayCount];
+    blackenObject(object);
+  }
+}
+
+static void sweep() {
+  Obj *previous = NULL;
+  Obj *object = vm.objects;
+  while (object != NULL) {
+    if (object->isMarked) {
+      object->isMarked = false;
+      previous = object;
+      object = object->next;
+    } else {
+      Obj *unreached = object;
+      object = object->next;
+      if (previous != NULL) {
+        previous->next = object;
+      } else {
+        vm.objects = object;
+      }
+
+      freeObject(unreached);
+    }
+  }
+}
+
+void collectGarbage() {
+#ifdef DEBUG_LOG_GC
+  printf("-- gc begin\n");
+  size_t before = vm.bytesAllocated;
+#endif
+
+  markRoots();
+  traceReferences();
+  tableRemoveWhite(&vm.strings);
+  sweep();
+
+  vm.nextGC = vm.bytesAllocated * GC_HEAP_GROW_FACTOR;
+
+#ifdef DEBUG_LOG_GC
+  printf("-- gc end\n");
+  printf("   collected %zu bytes (from %zu to %zu) next at %zu\n",
+         before - vm.bytesAllocated, before, vm.bytesAllocated, vm.nextGC);
+#endif
+}
diff --git a/src/memory.h b/src/memory.h
index d5b805d..6d59a02 100644
--- a/src/memory.h
+++ b/src/memory.h
@@ -1,12 +1,17 @@
-#ifndef ztl_memory_h
-#define ztl_memory_h
+#ifndef zlc_memory_h
+#define zlc_memory_h
 
 #include "common.h"
+#include "object.h"
+
+#define ALLOCATE(type, count) \
+    (type*)reallocate(NULL, 0, sizeof(type) * (count))
+
+#define FREE(type, pointer) reallocate(pointer, sizeof(type), 0)
 
 #define GROW_CAPACITY(capacity) \
     ((capacity) < 8 ? 8 : (capacity) * 2)
 
-
 #define GROW_ARRAY(type, pointer, oldCount, newCount) \
     (type*)reallocate(pointer, sizeof(type) * (oldCount), \
         sizeof(type) * (newCount))
@@ -15,7 +20,9 @@
     reallocate(pointer, sizeof(type) * (oldCount), 0)
 
 void* reallocate(void* pointer, size_t oldSize, size_t newSize);
-
+void markObject(Obj* object);
+void markValue(Value value);
+void collectGarbage();
+void freeObjects();
 
 #endif
-
diff --git a/src/object.c b/src/object.c
new file mode 100644
index 0000000..aa24c82
--- /dev/null
+++ b/src/object.c
@@ -0,0 +1,163 @@
+#include <stdio.h>
+#include <string.h>
+
+#include "memory.h"
+#include "object.h"
+#include "table.h"
+#include "value.h"
+#include "vm.h"
+
+#define ALLOCATE_OBJ(type, objectType)                                         \
+  (type *)allocateObject(sizeof(type), objectType)
+
+static Obj *allocateObject(size_t size, ObjType type) {
+  Obj *object = (Obj *)reallocate(NULL, 0, size);
+  object->type = type;
+  object->isMarked = false;
+  object->next = vm.objects;
+  vm.objects = object;
+
+#ifdef DEBUG_LOG_GC
+  printf("%p allocate %zu for %d\n", (void *)object, size, type);
+#endif
+
+  return object;
+}
+
+ObjBoundMethod *newBoundMethod(Value receiver, ObjClosure *method) {
+  ObjBoundMethod *bound = ALLOCATE_OBJ(ObjBoundMethod, OBJ_BOUND_METHOD);
+  bound->receiver = receiver;
+  bound->method = method;
+  return bound;
+}
+
+TypeObj *newType(ObjString *name) {
+  TypeObj *t = ALLOCATE_OBJ(TypeObj, OBJ_TYPE);
+  t->name = name;
+  initTable(&t->methods);
+  return t;
+}
+
+ObjClosure *newClosure(ObjFunction *function) {
+  ObjUpvalue **upvalues = ALLOCATE(ObjUpvalue *, function->upvalueCount);
+  for (int i = 0; i < function->upvalueCount; i++) {
+    upvalues[i] = NULL;
+  }
+
+  ObjClosure *closure = ALLOCATE_OBJ(ObjClosure, OBJ_CLOSURE);
+  closure->function = function;
+  closure->upvalues = upvalues;
+  closure->upvalueCount = function->upvalueCount;
+  return closure;
+}
+
+ObjFunction *newFunction() {
+  ObjFunction *function = ALLOCATE_OBJ(ObjFunction, OBJ_FUNCTION);
+  function->arity = 0;
+  function->upvalueCount = 0;
+  function->name = NULL;
+  initChunk(&function->chunk);
+  return function;
+}
+
+ObjInstance *newInstance(TypeObj *t) {
+  ObjInstance *instance = ALLOCATE_OBJ(ObjInstance, OBJ_INSTANCE);
+  instance->t = t;
+  initTable(&instance->fields);
+  return instance;
+}
+
+ObjNative *newNative(NativeFn function) {
+  ObjNative *native = ALLOCATE_OBJ(ObjNative, OBJ_NATIVE);
+  native->function = function;
+  return native;
+}
+
+static ObjString *allocateString(char *chars, int length, uint32_t hash) {
+  ObjString *string = ALLOCATE_OBJ(ObjString, OBJ_STRING);
+  string->length = length;
+  string->chars = chars;
+  string->hash = hash;
+  push(OBJ_VAL(string));
+  tableSet(&vm.strings, string, NIL_VAL);
+  pop();
+  return string;
+}
+
+static uint32_t hashString(const char *key, int length) {
+  uint32_t hash = 2166136261u;
+  for (int i = 0; i < length; i++) {
+    hash ^= (uint8_t)key[i];
+    hash *= 16777619;
+  }
+  return hash;
+}
+
+ObjString *takeString(char *chars, int length) {
+  uint32_t hash = hashString(chars, length);
+  ObjString *interned = tableFindString(&vm.strings, chars, length, hash);
+  if (interned != NULL) {
+    FREE_ARRAY(char, chars, length + 1);
+    return interned;
+  }
+
+  return allocateString(chars, length, hash);
+}
+
+ObjString *copyString(const char *chars, int length) {
+  uint32_t hash = hashString(chars, length);
+  ObjString *interned = tableFindString(&vm.strings, chars, length, hash);
+  if (interned != NULL)
+    return interned;
+
+  char *heapChars = ALLOCATE(char, length + 1);
+  memcpy(heapChars, chars, length);
+  heapChars[length] = '\0';
+  return allocateString(heapChars, length, hash);
+}
+
+ObjUpvalue *newUpvalue(Value *slot) {
+  ObjUpvalue *upvalue = ALLOCATE_OBJ(ObjUpvalue, OBJ_UPVALUE);
+  upvalue->closed = NIL_VAL;
+  upvalue->location = slot;
+  upvalue->next = NULL;
+  return upvalue;
+}
+
+static void printFunction(ObjFunction *function) {
+  if (function->name == NULL) {
+    printf("<script>");
+    return;
+  }
+
+  printf("<fn %s>", function->name->chars);
+}
+
+void printObject(Value value) {
+  switch (OBJ_TYPE(value)) {
+  case OBJ_BOUND_METHOD:
+    printFunction(AS_BOUND_METHOD(value)->method->function);
+    break;
+  case OBJ_TYPE:
+    printf("%s", AS_TYPE(value)->name->chars);
+    break;
+  case OBJ_CLOSURE:
+    printFunction(AS_CLOSURE(value)->function);
+    break;
+  case OBJ_FUNCTION:
+    printFunction(AS_FUNCTION(value));
+    break;
+  case OBJ_INSTANCE:
+    printf("%s instance", AS_INSTANCE(value)->t->name->chars);
+    break;
+  case OBJ_NATIVE:
+    printf("<native fn>");
+    break;
+  case OBJ_STRING:
+    printf("%s", AS_CSTRING(value));
+    break;
+  case OBJ_UPVALUE:
+    printf("upvalue");
+    break;
+  }
+}
diff --git a/src/object.h b/src/object.h
new file mode 100644
index 0000000..f4a49da
--- /dev/null
+++ b/src/object.h
@@ -0,0 +1,114 @@
+#ifndef zlc_object_h
+#define zlc_object_h
+
+#include "chunk.h"
+#include "common.h"
+#include "table.h"
+#include "value.h"
+
+#define OBJ_TYPE(value) (AS_OBJ(value)->type)
+
+#define IS_BOUND_METHOD(value) isObjType(value, OBJ_BOUND_METHOD)
+#define IS_TYPE(value) isObjType(value, OBJ_TYPE)
+#define IS_CLOSURE(value) isObjType(value, OBJ_CLOSURE)
+#define IS_FUNCTION(value) isObjType(value, OBJ_FUNCTION)
+#define IS_INSTANCE(value) isObjType(value, OBJ_INSTANCE)
+#define IS_NATIVE(value) isObjType(value, OBJ_NATIVE)
+#define IS_STRING(value) isObjType(value, OBJ_STRING)
+
+#define AS_BOUND_METHOD(value) ((ObjBoundMethod *)AS_OBJ(value))
+#define AS_TYPE(value) ((TypeObj *)AS_OBJ(value))
+#define AS_CLOSURE(value) ((ObjClosure *)AS_OBJ(value))
+#define AS_FUNCTION(value) ((ObjFunction *)AS_OBJ(value))
+#define AS_INSTANCE(value) ((ObjInstance *)AS_OBJ(value))
+#define AS_NATIVE(value) (((ObjNative *)AS_OBJ(value))->function)
+#define AS_STRING(value) ((ObjString *)AS_OBJ(value))
+#define AS_CSTRING(value) (((ObjString *)AS_OBJ(value))->chars)
+
+typedef enum {
+  OBJ_BOUND_METHOD,
+  OBJ_TYPE,
+  OBJ_CLOSURE,
+  OBJ_FUNCTION,
+  OBJ_INSTANCE,
+  OBJ_NATIVE,
+  OBJ_STRING,
+  OBJ_UPVALUE
+} ObjType;
+
+struct Obj {
+  ObjType type;
+  bool isMarked;
+  struct Obj *next;
+};
+
+typedef struct {
+  Obj obj;
+  int arity;
+  int upvalueCount;
+  Chunk chunk;
+  ObjString *name;
+} ObjFunction;
+
+typedef Value (*NativeFn)(int argCount, Value *args);
+
+typedef struct {
+  Obj obj;
+  NativeFn function;
+} ObjNative;
+
+struct ObjString {
+  Obj obj;
+  int length;
+  char *chars;
+  uint32_t hash;
+};
+
+typedef struct ObjUpvalue {
+  Obj obj;
+  Value *location;
+  Value closed;
+  struct ObjUpvalue *next;
+} ObjUpvalue;
+
+typedef struct {
+  Obj obj;
+  ObjFunction *function;
+  ObjUpvalue **upvalues;
+  int upvalueCount;
+} ObjClosure;
+
+typedef struct {
+  Obj obj;
+  ObjString *name;
+  Table methods;
+} TypeObj;
+
+typedef struct {
+  Obj obj;
+  TypeObj *t;
+  Table fields;
+} ObjInstance;
+
+typedef struct {
+  Obj obj;
+  Value receiver;
+  ObjClosure *method;
+} ObjBoundMethod;
+
+ObjBoundMethod *newBoundMethod(Value receiver, ObjClosure *method);
+TypeObj *newType(ObjString *name);
+ObjClosure *newClosure(ObjFunction *function);
+ObjFunction *newFunction();
+ObjInstance *newInstance(TypeObj *t);
+ObjNative *newNative(NativeFn function);
+ObjString *takeString(char *chars, int length);
+ObjString *copyString(const char *chars, int length);
+ObjUpvalue *newUpvalue(Value *slot);
+void printObject(Value value);
+
+static inline bool isObjType(Value value, ObjType type) {
+  return IS_OBJ(value) && AS_OBJ(value)->type == type;
+}
+
+#endif
diff --git a/src/scanner.c b/src/scanner.c
index 505167d..6b8a3aa 100644
--- a/src/scanner.c
+++ b/src/scanner.c
@@ -12,13 +12,43 @@ typedef struct {
 
 Scanner scanner;
 
-void newScanner(const char* source) {
+void initScanner(const char *source) {
   scanner.start = source;
   scanner.current = source;
   scanner.line = 1;
 }
 
-static Token newToken(TokenType type) {
+static bool isAlpha(char c) {
+  return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_';
+}
+
+static bool isDigit(char c) { return c >= '0' && c <= '9'; }
+
+static bool isAtEnd() { return *scanner.current == '\0'; }
+
+static char advance() {
+  scanner.current++;
+  return scanner.current[-1];
+}
+
+static char peek() { return *scanner.current; }
+
+static char peekNext() {
+  if (isAtEnd())
+    return '\0';
+  return scanner.current[1];
+}
+
+static bool match(char expected) {
+  if (isAtEnd())
+    return false;
+  if (*scanner.current != expected)
+    return false;
+  scanner.current++;
+  return true;
+}
+
+static Token makeToken(TokenType type) {
   Token token;
   token.type = type;
   token.start = scanner.start;
@@ -27,7 +57,7 @@ static Token newToken(TokenType type) {
   return token;
 }
 
-static Token errorToken(const char* message) {
+static Token errorToken(const char *message) {
   Token token;
   token.type = TOKEN_ERROR;
   token.start = message;
@@ -36,95 +66,34 @@ static Token errorToken(const char* message) {
   return token;
 }
 
-static bool isAtEnd() {
-  return *scanner.current == '\0';
-}
-
-static char peek() {
-  return *scanner.current;
-}
-
-static char peekNext() {
-  if (isAtEnd()) return '\0';
-  return scanner.current[1];
-}
-
-static char advance() {
-  scanner.current++;
-  return scanner.current[-1];
-}
-
-static bool match(char expected) {
-  if (isAtEnd()) return false;
-  if (*scanner.current != expected) return false;
-  scanner.current++;
-  return true;
-}
-
 static void skipWhitespace() {
   for (;;) {
     char c = peek();
     switch (c) {
-      case ' ':
-      case '\r':
-      case '\t':
-        advance();
-        break;
-      case '\n':
-        scanner.line++;
-        advance();
-        break;
-      case '/':
-        if (peekNext() == '/') {
-          // A comment goes until the end of the line.
-          while (peek() != '\n' && !isAtEnd()) advance();
-        } else {
-          return;
-        }
-        break;
-      default:
+    case ' ':
+    case '\r':
+    case '\t':
+      advance();
+      break;
+    case '\n':
+      scanner.line++;
+      advance();
+      break;
+    case '/':
+      if (peekNext() == '/') {
+        // A comment goes until the end of the line.
+        while (peek() != '\n' && !isAtEnd())
+          advance();
+      } else {
         return;
+      }
+      break;
+    default:
+      return;
     }
   }
 }
 
-static bool isDigit(char c) {
-  return c >= '0' && c <= '9';
-}
-
-static bool isAlpha(char c) {
-  return (c >= 'a' && c <= 'z') ||
-         (c >= 'A' && c <= 'Z') ||
-          c == '_';
-}
-
-static Token number() {
-  while (isDigit(peek())) advance();
-
-  // Look for a fractional part.
-  if (peek() == '.' && isDigit(peekNext())) {
-    // Consume the ".".
-    advance();
-
-    while (isDigit(peek())) advance();
-  }
-
-  return newToken(TOKEN_NUMBER);
-}
-
-static Token string() {
-  while (peek() != '"' && !isAtEnd()) {
-    if (peek() == '\n') scanner.line++;
-    advance();
-  }
-
-  if (isAtEnd()) return errorToken("Unterminated string.");
-
-  // The closing quote.
-  advance();
-  return newToken(TOKEN_STRING);
-}
-
 static TokenType checkKeyword(int start, int length, const char *rest,
                               TokenType type) {
   if (scanner.current - scanner.start == start + length &&
@@ -139,6 +108,8 @@ static TokenType identifierType() {
   switch (scanner.start[0]) {
   case 'a':
     return checkKeyword(1, 2, "nd", TOKEN_AND);
+  case 'b':
+    return checkKeyword(1, 4, "reak", TOKEN_BREAK);
   case 'e':
     return checkKeyword(1, 3, "lse", TOKEN_ELSE);
   case 'f':
@@ -181,60 +152,110 @@ static TokenType identifierType() {
   case 'w':
     return checkKeyword(1, 4, "hile", TOKEN_WHILE);
   }
+
   return TOKEN_IDENTIFIER;
 }
 
 static Token identifier() {
-  while (isAlpha(peek()) || isDigit(peek())) advance();
-  return newToken(identifierType());
+  while (isAlpha(peek()) || isDigit(peek()))
+    advance();
+  return makeToken(identifierType());
+}
+
+static Token number() {
+  while (isDigit(peek()))
+    advance();
+
+  // Look for a fractional part.
+  if (peek() == '.' && isDigit(peekNext())) {
+    // Consume the ".".
+    advance();
+
+    while (isDigit(peek()))
+      advance();
+  }
+
+  return makeToken(TOKEN_NUMBER);
+}
+
+static Token string() {
+  while (peek() != '"' && !isAtEnd()) {
+    if (peek() == '\n')
+      scanner.line++;
+    advance();
+  }
+
+  if (isAtEnd())
+    return errorToken("Unterminated string.");
+
+  // The closing quote.
+  advance();
+  return makeToken(TOKEN_STRING);
 }
 
 Token scanToken() {
   skipWhitespace();
   scanner.start = scanner.current;
 
-  if (isAtEnd()) return newToken(TOKEN_EOF);
+  if (isAtEnd())
+    return makeToken(TOKEN_EOF);
 
   char c = advance();
-  if (isAlpha(c)) return identifier();
-  if (isDigit(c)) return number();
+  if (isAlpha(c))
+    return identifier();
+  if (isDigit(c))
+    return number();
 
   switch (c) {
-    case '(': return newToken(TOKEN_LEFT_PAREN);
-    case ')': return newToken(TOKEN_RIGHT_PAREN);
-    case '{': return newToken(TOKEN_LEFT_BRACE);
-    case '}': return newToken(TOKEN_RIGHT_BRACE);
-    case '[': return newToken(TOKEN_LEFT_BRACKET);
-    case ']': return newToken(TOKEN_RIGHT_BRACKET);
-    case ';': return newToken(TOKEN_SEMICOLON);
-    case ':': return newToken(TOKEN_COLON);
-    case '#': return newToken(TOKEN_MESH);
-    case '$': return newToken(TOKEN_DOLLAR);
-    case '%': return newToken(TOKEN_PERCENT);
-    case '&': return newToken(TOKEN_AMPERSAND);
-    case '@': return newToken(TOKEN_AT);
-    case ',': return newToken(TOKEN_COMMA);
-    case '.': return newToken(TOKEN_DOT);
-    case '-': return newToken(TOKEN_MINUS);
-    case '+': return newToken(TOKEN_PLUS);
-    case '/': return newToken(TOKEN_SLASH);
-    case '*': return newToken(TOKEN_STAR);
-    case '!':
-      return newToken(
-          match('=') ? TOKEN_BANG_EQUAL : TOKEN_BANG);
-    case '=':
-      return newToken(
-          match('=') ? TOKEN_EQUAL_EQUAL : TOKEN_EQUAL);
-    case '<':
-      return newToken(
-          match('=') ? TOKEN_LESS_EQUAL : TOKEN_LESS);
-    case '>':
-      return newToken(
-          match('=') ? TOKEN_GREATER_EQUAL : TOKEN_GREATER);
-
-    case '"': return string();
+  case '(':
+    return makeToken(TOKEN_LEFT_PAREN);
+  case ')':
+    return makeToken(TOKEN_RIGHT_PAREN);
+  case '{':
+    return makeToken(TOKEN_LEFT_BRACE);
+  case '}':
+    return makeToken(TOKEN_RIGHT_BRACE);
+  case '[':
+    return makeToken(TOKEN_LEFT_BRACKET);
+  case ']':
+    return makeToken(TOKEN_RIGHT_BRACKET);
+  case ';':
+    return makeToken(TOKEN_SEMICOLON);
+  case ':':
+    return makeToken(TOKEN_COLON);
+  case '#':
+    return makeToken(TOKEN_MESH);
+  case '$':
+    return makeToken(TOKEN_DOLLAR);
+  case '%':
+    return makeToken(TOKEN_PERCENT);
+  case '&':
+    return makeToken(TOKEN_AMPERSAND);
+  case '@':
+    return makeToken(TOKEN_AT);
+  case ',':
+    return makeToken(TOKEN_COMMA);
+  case '.':
+    return makeToken(TOKEN_DOT);
+  case '-':
+    return makeToken(TOKEN_MINUS);
+  case '+':
+    return makeToken(TOKEN_PLUS);
+  case '/':
+    return makeToken(TOKEN_SLASH);
+  case '*':
+    return makeToken(TOKEN_STAR);
+  case '!':
+    return makeToken(match('=') ? TOKEN_BANG_EQUAL : TOKEN_BANG);
+  case '=':
+    return makeToken(match('=') ? TOKEN_EQUAL_EQUAL : TOKEN_EQUAL);
+  case '<':
+    return makeToken(match('=') ? TOKEN_LESS_EQUAL : TOKEN_LESS);
+  case '>':
+    return makeToken(match('=') ? TOKEN_GREATER_EQUAL : TOKEN_GREATER);
+  case '"':
+    return string();
   }
 
   return errorToken("Unexpected character.");
 }
-
diff --git a/src/scanner.h b/src/scanner.h
index 70c9f4f..280951e 100644
--- a/src/scanner.h
+++ b/src/scanner.h
@@ -1,5 +1,5 @@
-#ifndef ztl_scanner_h
-#define ztl_scanner_h
+#ifndef zlc_scanner_h
+#define zlc_scanner_h
 
 typedef enum {
   // End of file
@@ -54,6 +54,7 @@ typedef enum {
   TOKEN_TRUE,
   TOKEN_LET,
   TOKEN_WHILE,
+  TOKEN_BREAK,
   TOKEN_ERROR,
 } TokenType;
 
@@ -64,7 +65,7 @@ typedef struct {
   int line;
 } Token;
 
-void newScanner(const char *source);
+void initScanner(const char *source);
 Token scanToken();
 
 #endif
diff --git a/src/table.c b/src/table.c
new file mode 100644
index 0000000..cc634f7
--- /dev/null
+++ b/src/table.c
@@ -0,0 +1,151 @@
+#include <stdlib.h>
+#include <string.h>
+
+#include "memory.h"
+#include "object.h"
+#include "table.h"
+#include "value.h"
+
+#define TABLE_MAX_LOAD 0.75
+
+void initTable(Table* table) {
+  table->count = 0;
+  table->capacity = 0;
+  table->entries = NULL;
+}
+
+void freeTable(Table* table) {
+  FREE_ARRAY(Entry, table->entries, table->capacity);
+  initTable(table);
+}
+
+static Entry* findEntry(Entry* entries, int capacity,
+                        ObjString* key) {
+  uint32_t index = key->hash % capacity;
+  Entry* tombstone = NULL;
+  for (;;) {
+    Entry* entry = &entries[index];
+    if (entry->key == NULL) {
+      if (IS_NIL(entry->value)) {
+        // Empty entry.
+        return tombstone != NULL ? tombstone : entry;
+      } else {
+        // We found a tombstone.
+        if (tombstone == NULL) tombstone = entry;
+      }
+    } else if (entry->key == key) {
+      // We found the key.
+      return entry;
+    }
+
+    index = (index + 1) % capacity;
+  }
+}
+
+bool tableGet(Table* table, ObjString* key, Value* value) {
+  if (table->count == 0) return false;
+
+  Entry* entry = findEntry(table->entries, table->capacity, key);
+  if (entry->key == NULL) return false;
+
+  *value = entry->value;
+  return true;
+}
+
+static void adjustCapacity(Table* table, int capacity) {
+  Entry* entries = ALLOCATE(Entry, capacity);
+  for (int i = 0; i < capacity; i++) {
+    entries[i].key = NULL;
+    entries[i].value = NIL_VAL;
+  }
+
+  table->count = 0;
+  for (int i = 0; i < table->capacity; i++) {
+    Entry* entry = &table->entries[i];
+    if (entry->key == NULL) continue;
+
+    Entry* dest = findEntry(entries, capacity, entry->key);
+    dest->key = entry->key;
+    dest->value = entry->value;
+    table->count++;
+  }
+
+  FREE_ARRAY(Entry, table->entries, table->capacity);
+  table->entries = entries;
+  table->capacity = capacity;
+}
+
+bool tableSet(Table* table, ObjString* key, Value value) {
+  if (table->count + 1 > table->capacity * TABLE_MAX_LOAD) {
+    int capacity = GROW_CAPACITY(table->capacity);
+    adjustCapacity(table, capacity);
+  }
+
+  Entry* entry = findEntry(table->entries, table->capacity, key);
+  bool isNewKey = entry->key == NULL;
+  if (isNewKey && IS_NIL(entry->value)) table->count++;
+
+  entry->key = key;
+  entry->value = value;
+  return isNewKey;
+}
+
+bool tableDelete(Table* table, ObjString* key) {
+  if (table->count == 0) return false;
+
+  // Find the entry.
+  Entry* entry = findEntry(table->entries, table->capacity, key);
+  if (entry->key == NULL) return false;
+
+  // Place a tombstone in the entry.
+  entry->key = NULL;
+  entry->value = BOOL_VAL(true);
+  return true;
+}
+
+void tableAddAll(Table* from, Table* to) {
+  for (int i = 0; i < from->capacity; i++) {
+    Entry* entry = &from->entries[i];
+    if (entry->key != NULL) {
+      tableSet(to, entry->key, entry->value);
+    }
+  }
+}
+
+ObjString* tableFindString(Table* table, const char* chars,
+                           int length, uint32_t hash) {
+  if (table->count == 0) return NULL;
+
+  uint32_t index = hash % table->capacity;
+  for (;;) {
+    Entry* entry = &table->entries[index];
+    if (entry->key == NULL) {
+      // Stop if we find an empty non-tombstone entry.
+      if (IS_NIL(entry->value)) return NULL;
+    } else if (entry->key->length == length &&
+        entry->key->hash == hash &&
+        memcmp(entry->key->chars, chars, length) == 0) {
+      // We found it.
+      return entry->key;
+    }
+
+    index = (index + 1) % table->capacity;
+  }
+}
+
+void tableRemoveWhite(Table* table) {
+  for (int i = 0; i < table->capacity; i++) {
+    Entry* entry = &table->entries[i];
+    if (entry->key != NULL && !entry->key->obj.isMarked) {
+      tableDelete(table, entry->key);
+    }
+  }
+}
+
+void markTable(Table* table) {
+  for (int i = 0; i < table->capacity; i++) {
+    Entry* entry = &table->entries[i];
+    markObject((Obj*)entry->key);
+    markValue(entry->value);
+  }
+}
diff --git a/src/table.h b/src/table.h
new file mode 100644
index 0000000..c1142b5
--- /dev/null
+++ b/src/table.h
@@ -0,0 +1,29 @@
+#ifndef zlc_table_h
+#define zlc_table_h
+
+#include "common.h"
+#include "value.h"
+
+typedef struct {
+  ObjString* key;
+  Value value;
+} Entry;
+
+typedef struct {
+  int count;
+  int capacity;
+  Entry* entries;
+} Table;
+
+void initTable(Table* table);
+void freeTable(Table* table);
+bool tableGet(Table* table, ObjString* key, Value* value);
+bool tableSet(Table* table, ObjString* key, Value value);
+bool tableDelete(Table* table, ObjString* key);
+void tableAddAll(Table* from, Table* to);
+ObjString* tableFindString(Table* table, const char* chars,
+                           int length, uint32_t hash);
+void tableRemoveWhite(Table* table);
+void markTable(Table* table);
+
+#endif
diff --git a/src/value.c b/src/value.c
index 13d4591..627a8ef 100644
--- a/src/value.c
+++ b/src/value.c
@@ -1,15 +1,17 @@
 #include <stdio.h>
+#include <string.h>
 
+#include "object.h"
 #include "memory.h"
 #include "value.h"
 
-void newValueArray(ValueArray *array) {
+void initValueArray(ValueArray* array) {
   array->values = NULL;
   array->capacity = 0;
   array->count = 0;
 }
 
-void writeValueArray(ValueArray *array, Value value) {
+void writeValueArray(ValueArray* array, Value value) {
   if (array->capacity < array->count + 1) {
     int oldCapacity = array->capacity;
     array->capacity = GROW_CAPACITY(oldCapacity);
@@ -21,9 +23,9 @@ void writeValueArray(ValueArray *array, Value value) {
   array->count++;
 }
 
-void freeValueArray(ValueArray *array) {
+void freeValueArray(ValueArray* array) {
   FREE_ARRAY(Value, array->values, array->capacity);
-  newValueArray(array);
+  initValueArray(array);
 }
 
 void printValue(Value value) {
@@ -33,6 +35,7 @@ void printValue(Value value) {
       break;
     case VAL_NIL: printf("nil"); break;
     case VAL_NUMBER: printf("%g", AS_NUMBER(value)); break;
+    case VAL_OBJ: printObject(value); break;
   }
 }
 
@@ -42,6 +45,7 @@ bool valuesEqual(Value a, Value b) {
     case VAL_BOOL:   return AS_BOOL(a) == AS_BOOL(b);
     case VAL_NIL:    return true;
     case VAL_NUMBER: return AS_NUMBER(a) == AS_NUMBER(b);
+    case VAL_OBJ:    return AS_OBJ(a) == AS_OBJ(b);
     default:         return false; // Unreachable.
   }
 }
diff --git a/src/value.h b/src/value.h
index 19ac3b5..9376112 100644
--- a/src/value.h
+++ b/src/value.h
@@ -1,12 +1,16 @@
-#ifndef ztl_value_h
-#define ztl_value_h
+#ifndef zlc_value_h
+#define zlc_value_h
 
 #include "common.h"
 
+typedef struct Obj Obj;
+typedef struct ObjString ObjString;
+
 typedef enum {
   VAL_BOOL,
   VAL_NIL, 
   VAL_NUMBER,
+  VAL_OBJ,
 } ValueType;
 
 typedef struct {
@@ -14,30 +18,35 @@ typedef struct {
   union {
     bool boolean;
     double number;
+    Obj* obj;
   } as; 
 } Value;
 
-#define BOOL_VAL(value)   ((Value){VAL_BOOL,{.boolean = value}})
+
+#define IS_BOOL(value)    ((value).type == VAL_BOOL)
+#define IS_NIL(value)     ((value).type == VAL_NIL)
+#define IS_NUMBER(value)  ((value).type == VAL_NUMBER)
+#define IS_OBJ(value)     ((value).type == VAL_OBJ)
+
+#define AS_BOOL(value)    ((value).as.boolean)
+#define AS_NUMBER(value)  ((value).as.number)
+#define AS_OBJ(value)     ((value).as.obj)
+
+#define BOOL_VAL(value)   ((Value){VAL_BOOL, {.boolean = value}})
 #define NIL_VAL           ((Value){VAL_NIL, {.number = 0}})
-#define NUMBER_VAL(value) ((Value){VAL_NUMBER, {.number = value}}) 
-
-#define AS_BOOL(value)   ((value).as.boolean)
-#define AS_NUMBER(value) ((value).as.number) 
-
-#define IS_BOOL(value)   ((value).type == VAL_BOOL)
-#define IS_NIL(value)    ((value).type == VAL_NIL)
-#define IS_NUMBER(value) ((value).type == VAL_NUMBER) 
+#define NUMBER_VAL(value) ((Value){VAL_NUMBER, {.number = value}})
+#define OBJ_VAL(object)   ((Value){VAL_OBJ, {.obj = (Obj*)object}})
 
 typedef struct {
   int capacity;
   int count;
-  Value *values;
+  Value* values;
 } ValueArray;
 
 bool valuesEqual(Value a, Value b);
-void newValueArray(ValueArray *array);
-void writeValueArray(ValueArray *array, Value value);
-void freeValueArray(ValueArray *array);
+void initValueArray(ValueArray* array);
+void writeValueArray(ValueArray* array, Value value);
+void freeValueArray(ValueArray* array);
 void printValue(Value value);
 
 #endif
diff --git a/src/vm.c b/src/vm.c
index da00e48..e02c542 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1,36 +1,54 @@
+#include "vm.h"
 #include "common.h"
 #include "compiler.h"
 #include "debug.h"
-#include "vm.h"
+#include "memory.h"
+#include "object.h"
 
-#include <stdio.h>
 #include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
 
-VM vm; 
+VM vm;
+
+static Value clockNative(int argCount, Value *args) {
+  return NUMBER_VAL((double)clock() / CLOCKS_PER_SEC);
+}
 
 static void resetStack() {
   vm.stackTop = vm.stack;
+  vm.frameCount = 0;
+  vm.openUpvalues = NULL;
 }
 
-static void runtimeError(const char* format, ...) {
+static void runtimeError(const char *format, ...) {
   va_list args;
   va_start(args, format);
   vfprintf(stderr, format, args);
   va_end(args);
   fputs("\n", stderr);
 
-  size_t instruction = vm.ip - vm.chunk->code - 1;
-  int line = vm.chunk->lines[instruction];
-  fprintf(stderr, "[line %d] in script\n", line);
+  for (int i = vm.frameCount - 1; i >= 0; i--) {
+    CallFrame *frame = &vm.frames[i];
+    ObjFunction *function = frame->closure->function;
+    size_t instruction = frame->ip - function->chunk.code - 1;
+    fprintf(stderr, "[line %d] in ", function->chunk.lines[instruction]);
+    if (function->name == NULL) {
+      fprintf(stderr, "script\n");
+    } else {
+      fprintf(stderr, "%s()\n", function->name->chars);
+    }
+  }
   resetStack();
 }
 
-void newVM() {
-  resetStack();
-}
-
-void freeVM() {
-
+static void defineNative(const char *name, NativeFn function) {
+  push(OBJ_VAL(copyString(name, (int)strlen(name))));
+  push(OBJ_VAL(newNative(function)));
+  tableSet(&vm.globals, AS_STRING(vm.stack[0]), vm.stack[1]);
+  pop();
+  pop();
 }
 
 void push(Value value) {
@@ -43,102 +61,456 @@ Value pop() {
   return *vm.stackTop;
 }
 
-static Value peek(int distance) {
-  return vm.stackTop[-1 - distance];
+static Value peek(int distance) { return vm.stackTop[-1 - distance]; }
+
+static bool call(ObjClosure *closure, int argCount) {
+  if (argCount != closure->function->arity) {
+    runtimeError("Expected %d arguments but got %d.", closure->function->arity,
+                 argCount);
+    return false;
+  }
+  if (vm.frameCount == FRAMES_MAX) {
+    runtimeError("Stack overflow.");
+    return false;
+  }
+
+  CallFrame *frame = &vm.frames[vm.frameCount++];
+  frame->closure = closure;
+  frame->ip = closure->function->chunk.code;
+  frame->slots = vm.stackTop - argCount - 1;
+  return true;
+}
+
+static bool callValue(Value callee, int argCount) {
+  if (IS_OBJ(callee)) {
+    switch (OBJ_TYPE(callee)) {
+    case OBJ_BOUND_METHOD: {
+      ObjBoundMethod *bound = AS_BOUND_METHOD(callee);
+      vm.stackTop[-argCount - 1] = bound->receiver;
+      return call(bound->method, argCount);
+    }
+    case OBJ_TYPE: {
+      TypeObj *t = AS_TYPE(callee);
+      vm.stackTop[-argCount - 1] = OBJ_VAL(newInstance(t));
+      Value initializer;
+      if (tableGet(&t->methods, vm.initString, &initializer)) {
+        return call(AS_CLOSURE(initializer), argCount);
+      } else if (argCount != 0) {
+        runtimeError("Expected 0 arguments but got %d.", argCount);
+        return false;
+      }
+      return true;
+    }
+    case OBJ_CLOSURE:
+      return call(AS_CLOSURE(callee), argCount);
+    case OBJ_NATIVE: {
+      NativeFn native = AS_NATIVE(callee);
+      Value result = native(argCount, vm.stackTop - argCount);
+      vm.stackTop -= argCount + 1;
+      push(result);
+      return true;
+    }
+    default:
+      break; // Non-callable object type.
+    }
+  }
+  runtimeError("Can only call functions and typees.");
+  return false;
+}
+
+static bool invokeFromType(TypeObj *t, ObjString *name, int argCount) {
+  Value method;
+  if (!tableGet(&t->methods, name, &method)) {
+    runtimeError("Undefined property '%s'.", name->chars);
+    return false;
+  }
+  return call(AS_CLOSURE(method), argCount);
+}
+
+static bool invoke(ObjString *name, int argCount) {
+  Value receiver = peek(argCount);
+  if (!IS_INSTANCE(receiver)) {
+    runtimeError("Only instances have methods.");
+    return false;
+  }
+
+  ObjInstance *instance = AS_INSTANCE(receiver);
+  Value value;
+  if (tableGet(&instance->fields, name, &value)) {
+    vm.stackTop[-argCount - 1] = value;
+    return callValue(value, argCount);
+  }
+  return invokeFromType(instance->t, name, argCount);
+}
+
+static bool bindMethod(TypeObj *t, ObjString *name) {
+  Value method;
+  if (!tableGet(&t->methods, name, &method)) {
+    runtimeError("Undefined property '%s'.", name->chars);
+    return false;
+  }
+
+  ObjBoundMethod *bound = newBoundMethod(peek(0), AS_CLOSURE(method));
+  pop();
+  push(OBJ_VAL(bound));
+  return true;
+}
+
+static ObjUpvalue *captureUpvalue(Value *local) {
+  ObjUpvalue *prevUpvalue = NULL;
+  ObjUpvalue *upvalue = vm.openUpvalues;
+  while (upvalue != NULL && upvalue->location > local) {
+    prevUpvalue = upvalue;
+    upvalue = upvalue->next;
+  }
+
+  if (upvalue != NULL && upvalue->location == local) {
+    return upvalue;
+  }
+
+  ObjUpvalue *createdUpvalue = newUpvalue(local);
+  createdUpvalue->next = upvalue;
+
+  if (prevUpvalue == NULL) {
+    vm.openUpvalues = createdUpvalue;
+  } else {
+    prevUpvalue->next = createdUpvalue;
+  }
+  return createdUpvalue;
+}
+
+static void closeUpvalues(Value *last) {
+  while (vm.openUpvalues != NULL && vm.openUpvalues->location >= last) {
+    ObjUpvalue *upvalue = vm.openUpvalues;
+    upvalue->closed = *upvalue->location;
+    upvalue->location = &upvalue->closed;
+    vm.openUpvalues = upvalue->next;
+  }
+}
+
+static void defineMethod(ObjString *name) {
+  Value method = peek(0);
+  TypeObj *t = AS_TYPE(peek(1));
+  tableSet(&t->methods, name, method);
+  pop();
 }
 
 static bool isFalsey(Value value) {
   return IS_NIL(value) || (IS_BOOL(value) && !AS_BOOL(value));
 }
 
+static void concatenate() {
+  ObjString *b = AS_STRING(peek(0));
+  ObjString *a = AS_STRING(peek(1));
+
+  int length = a->length + b->length;
+  char *chars = ALLOCATE(char, length + 1);
+  memcpy(chars, a->chars, a->length);
+  memcpy(chars + a->length, b->chars, b->length);
+  chars[length] = '\0';
+
+  ObjString *result = takeString(chars, length);
+  pop();
+  pop();
+  push(OBJ_VAL(result));
+}
+
+void initVM() {
+  resetStack();
+  vm.objects = NULL;
+  vm.bytesAllocated = 0;
+  vm.nextGC = 1024 * 1024;
+  vm.grayCount = 0;
+  vm.grayCapacity = 0;
+  vm.grayStack = NULL;
+
+  initTable(&vm.globals);
+  initTable(&vm.strings);
+
+  vm.initString = NULL;
+  vm.initString = copyString("init", 4);
+
+  defineNative("clock", clockNative);
+}
+
+void freeVM() {
+  freeTable(&vm.globals);
+  freeTable(&vm.strings);
+  vm.initString = NULL;
+  freeObjects();
+}
+
 static InterpretResult run() {
-#define READ_BYTE() (*vm.ip++)
-#define READ_CONSTANT() (vm.chunk->constants.values[READ_BYTE()])
-#define BINARY_OP(valueType, op) \
-    do { \
-      if (!IS_NUMBER(peek(0)) || !IS_NUMBER(peek(1))) { \
-        runtimeError("Operands must be numbers."); \
-        return INTERPRET_RUNTIME_ERROR; \
-      } \
-      double b = AS_NUMBER(pop()); \
-      double a = AS_NUMBER(pop()); \
-      push(valueType(a op b)); \
-    } while (false)
+  CallFrame *frame = &vm.frames[vm.frameCount - 1];
+
+#define READ_BYTE() (*frame->ip++)
+#define READ_SHORT()                                                           \
+  (frame->ip += 2, (uint16_t)((frame->ip[-2] << 8) | frame->ip[-1]))
+#define READ_CONSTANT()                                                        \
+  (frame->closure->function->chunk.constants.values[READ_BYTE()])
+#define READ_STRING() AS_STRING(READ_CONSTANT())
+#define BINARY_OP(valueType, op)                                               \
+  do {                                                                         \
+    if (!IS_NUMBER(peek(0)) || !IS_NUMBER(peek(1))) {                          \
+      runtimeError("Operands must be numbers.");                               \
+      return INTERPRET_RUNTIME_ERROR;                                          \
+    }                                                                          \
+    double b = AS_NUMBER(pop());                                               \
+    double a = AS_NUMBER(pop());                                               \
+    push(valueType(a op b));                                                   \
+  } while (false)
 
   for (;;) {
 #ifdef DEBUG_TRACE_EXECUTION
     printf("          ");
-    for (Value* slot = vm.stack; slot < vm.stackTop; slot++) {
+    for (Value *slot = vm.stack; slot < vm.stackTop; slot++) {
       printf("[ ");
       printValue(*slot);
       printf(" ]");
     }
     printf("\n");
-    disassembleInstruction(vm.chunk,
-                           (int)(vm.ip - vm.chunk->code));
+    disassembleInstruction(
+        &frame->closure->function->chunk,
+        (int)(frame->ip - frame->closure->function->chunk.code));
 #endif
-
     uint8_t instruction;
     switch (instruction = READ_BYTE()) {
-      case OP_CONSTANT: {
-        Value constant = READ_CONSTANT();
-	push(constant);
+    case OP_CONSTANT: {
+      Value constant = READ_CONSTANT();
+      push(constant);
+      break;
+    }
+    case OP_NIL:
+      push(NIL_VAL);
+      break;
+    case OP_TRUE:
+      push(BOOL_VAL(true));
+      break;
+    case OP_FALSE:
+      push(BOOL_VAL(false));
+      break;
+    case OP_POP:
+      pop();
+      break;
+    case OP_GET_LOCAL: {
+      uint8_t slot = READ_BYTE();
+      push(frame->slots[slot]);
+      break;
+    }
+    case OP_SET_LOCAL: {
+      uint8_t slot = READ_BYTE();
+      vm.stack[slot] = peek(0);
+      break;
+    }
+    case OP_GET_GLOBAL: {
+      ObjString *name = READ_STRING();
+      Value value;
+      if (!tableGet(&vm.globals, name, &value)) {
+        runtimeError("Undefined variable '%s'.", name->chars);
+        return INTERPRET_RUNTIME_ERROR;
+      }
+      push(value);
+      break;
+    }
+    case OP_DEFINE_GLOBAL: {
+      ObjString *name = READ_STRING();
+      tableSet(&vm.globals, name, peek(0));
+      pop();
+      break;
+    }
+    case OP_SET_GLOBAL: {
+      ObjString *name = READ_STRING();
+      if (tableSet(&vm.globals, name, peek(0))) {
+        tableDelete(&vm.globals, name);
+        runtimeError("Undefined variable '%s'.", name->chars);
+        return INTERPRET_RUNTIME_ERROR;
+      }
+      break;
+    }
+    case OP_GET_UPVALUE: {
+      uint8_t slot = READ_BYTE();
+      push(*frame->closure->upvalues[slot]->location);
+      break;
+    }
+    case OP_SET_UPVALUE: {
+      uint8_t slot = READ_BYTE();
+      *frame->closure->upvalues[slot]->location = peek(0);
+      break;
+    }
+    case OP_GET_PROPERTY: {
+      if (!IS_INSTANCE(peek(0))) {
+        runtimeError("Only instances have properties.");
+        return INTERPRET_RUNTIME_ERROR;
+      }
+
+      ObjInstance *instance = AS_INSTANCE(peek(0));
+      ObjString *name = READ_STRING();
+
+      Value value;
+      if (tableGet(&instance->fields, name, &value)) {
+        pop(); // Instance.
+        push(value);
         break;
       }
-      case OP_NIL: push(NIL_VAL); break;
-      case OP_TRUE: push(BOOL_VAL(true)); break;
-      case OP_FALSE: push(BOOL_VAL(false)); break;
-      case OP_EQUAL: {
-        Value b = pop();
-        Value a = pop();
-        push(BOOL_VAL(valuesEqual(a, b)));
-        break;
+
+      if (!bindMethod(instance->t, name)) {
+        return INTERPRET_RUNTIME_ERROR;
       }
-      case OP_GREATER:  BINARY_OP(BOOL_VAL, >); break;
-      case OP_LESS:     BINARY_OP(BOOL_VAL, <); break;
-      case OP_ADD:      BINARY_OP(NUMBER_VAL, +); break;
-      case OP_SUBTRACT: BINARY_OP(NUMBER_VAL, -); break;
-      case OP_MULTIPLY: BINARY_OP(NUMBER_VAL, *); break;
-      case OP_DIVIDE:   BINARY_OP(NUMBER_VAL, /); break;
-      case OP_NOT:
-        push(BOOL_VAL(isFalsey(pop())));
-        break;
-      case OP_NEGATE:
-        if (!IS_NUMBER(peek(0))) {
-          runtimeError("Operand must be a number.");
-          return INTERPRET_RUNTIME_ERROR;
+      break;
+    }
+    case OP_SET_PROPERTY: {
+      if (!IS_INSTANCE(peek(1))) {
+        runtimeError("Only instances have fields.");
+        return INTERPRET_RUNTIME_ERROR;
+      }
+
+      ObjInstance *instance = AS_INSTANCE(peek(1));
+      tableSet(&instance->fields, READ_STRING(), peek(0));
+      Value value = pop();
+      pop();
+      push(value);
+      break;
+    }
+    case OP_EQUAL: {
+      Value b = pop();
+      Value a = pop();
+      push(BOOL_VAL(valuesEqual(a, b)));
+      break;
+    }
+    case OP_GREATER:
+      BINARY_OP(BOOL_VAL, >);
+      break;
+    case OP_LESS:
+      BINARY_OP(BOOL_VAL, <);
+      break;
+    case OP_ADD: {
+      if (IS_STRING(peek(0)) && IS_STRING(peek(1))) {
+        concatenate();
+      } else if (IS_NUMBER(peek(0)) && IS_NUMBER(peek(1))) {
+        double b = AS_NUMBER(pop());
+        double a = AS_NUMBER(pop());
+        push(NUMBER_VAL(a + b));
+      } else {
+        runtimeError("Operands must be two numbers or two strings.");
+        return INTERPRET_RUNTIME_ERROR;
+      }
+      break;
+    }
+    case OP_SUBTRACT:
+      BINARY_OP(NUMBER_VAL, -);
+      break;
+    case OP_MULTIPLY:
+      BINARY_OP(NUMBER_VAL, *);
+      break;
+    case OP_DIVIDE:
+      BINARY_OP(NUMBER_VAL, /);
+      break;
+    case OP_NOT:
+      push(BOOL_VAL(isFalsey(pop())));
+      break;
+    case OP_NEGATE:
+      if (!IS_NUMBER(peek(0))) {
+        runtimeError("Operand must be a number.");
+        return INTERPRET_RUNTIME_ERROR;
+      }
+      push(NUMBER_VAL(-AS_NUMBER(pop())));
+      break;
+    case OP_PRINT: {
+      printValue(pop());
+      printf("\n");
+      break;
+    }
+    case OP_JUMP: {
+      uint16_t offset = READ_SHORT();
+      frame->ip += offset;
+      break;
+    }
+    case OP_JUMP_IF_FALSE: {
+      uint16_t offset = READ_SHORT();
+      if (isFalsey(peek(0)))
+        frame->ip += offset;
+      break;
+    }
+    case OP_LOOP: {
+      uint16_t offset = READ_SHORT();
+      frame->ip -= offset;
+      break;
+    }
+    case OP_CALL: {
+      int argCount = READ_BYTE();
+      if (!callValue(peek(argCount), argCount)) {
+        return INTERPRET_RUNTIME_ERROR;
+      }
+      frame = &vm.frames[vm.frameCount - 1];
+      break;
+    }
+    case OP_INVOKE: {
+      ObjString *method = READ_STRING();
+      int argCount = READ_BYTE();
+      if (!invoke(method, argCount)) {
+        return INTERPRET_RUNTIME_ERROR;
+      }
+      frame = &vm.frames[vm.frameCount - 1];
+      break;
+    }
+    case OP_CLOSURE: {
+      ObjFunction *function = AS_FUNCTION(READ_CONSTANT());
+      ObjClosure *closure = newClosure(function);
+      push(OBJ_VAL(closure));
+      for (int i = 0; i < closure->upvalueCount; i++) {
+        uint8_t isLocal = READ_BYTE();
+        uint8_t index = READ_BYTE();
+        if (isLocal) {
+          closure->upvalues[i] = captureUpvalue(frame->slots + index);
+        } else {
+          closure->upvalues[i] = frame->closure->upvalues[index];
         }
-        push(NUMBER_VAL(-AS_NUMBER(pop())));
-        break;
-      case OP_RETURN: {
-	printValue(pop());
-	printf("\n");
+      }
+      break;
+    }
+    case OP_CLOSE_UPVALUE:
+      closeUpvalues(vm.stackTop - 1);
+      pop();
+      break;
+    case OP_TYPE:
+      push(OBJ_VAL(newType(READ_STRING())));
+      break;
+    case OP_METHOD:
+      defineMethod(READ_STRING());
+      break;
+    case OP_RETURN:
+      Value result = pop();
+      closeUpvalues(frame->slots);
+      vm.frameCount--;
+      if (vm.frameCount == 0) {
+        pop();
         return INTERPRET_OK;
       }
+
+      vm.stackTop = frame->slots;
+      push(result);
+      frame = &vm.frames[vm.frameCount - 1];
+      break;
     }
   }
 
 #undef READ_BYTE
+#undef READ_SHORT
 #undef READ_CONSTANT
+#undef READ_STRING
 #undef BINARY_OP
 }
 
-InterpretResult interpret(const char* source) {
-  Chunk chunk;
-  newChunk(&chunk);
-
-  if (!compile(source, &chunk)) {
-    freeChunk(&chunk);
+InterpretResult interpret(const char *source) {
+  ObjFunction *function = compile(source);
+  if (function == NULL)
     return INTERPRET_COMPILE_ERROR;
-  }
 
-  vm.chunk = &chunk;
-  vm.ip = vm.chunk->code;
+  push(OBJ_VAL(function));
+  ObjClosure *closure = newClosure(function);
+  pop();
+  push(OBJ_VAL(closure));
+  call(closure, 0);
 
-  InterpretResult result = run();
-
-  freeChunk(&chunk);
-  return result;
+  return run();
 }
-
-
diff --git a/src/vm.h b/src/vm.h
index 50cd09b..83b76a8 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -1,16 +1,36 @@
-#ifndef ztl_vm_h
-#define ztl_vm_h
+#ifndef zlc_vm_h
+#define zlc_vm_h
 
-#include "chunk.h"
+#include "object.h"
+#include "table.h"
 #include "value.h"
 
-#define STACK_MAX 256
+#define FRAMES_MAX 64
+#define STACK_MAX (FRAMES_MAX * UINT8_COUNT)
 
 typedef struct {
-  Chunk *chunk;
-  uint8_t *ip;
+  ObjClosure* closure;
+  uint8_t* ip;
+  Value* slots;
+} CallFrame;
+
+typedef struct {
+  CallFrame frames[FRAMES_MAX];
+  int frameCount;
+
   Value stack[STACK_MAX];
-  Value *stackTop;
+  Value* stackTop;
+  Table globals;
+  Table strings;
+  ObjString* initString;
+  ObjUpvalue* openUpvalues;
+
+  size_t bytesAllocated;
+  size_t nextGC;
+  Obj* objects;
+  int grayCount;
+  int grayCapacity;
+  Obj** grayStack;
 } VM;
 
 typedef enum {
@@ -19,11 +39,12 @@ typedef enum {
   INTERPRET_RUNTIME_ERROR
 } InterpretResult;
 
-void newVM();
+extern VM vm;
+
+void initVM();
 void freeVM();
 InterpretResult interpret(const char* source);
 void push(Value value);
 Value pop();
 
 #endif
-