diff --git a/clox/chunk.h b/clox/chunk.h
index 2b3798f..34d73c4 100644
--- a/clox/chunk.h
+++ b/clox/chunk.h
@@ -6,12 +6,19 @@
 
 typedef enum {
   OP_CONSTANT,
+  OP_NIL,
+  OP_TRUE,
+  OP_FALSE,
+  OP_EQUAL,
+  OP_GREATER,
+  OP_LESS,
   OP_RETURN,
   OP_NEGATE,
   OP_ADD,
   OP_SUBTRACT,
   OP_MULTIPLY,
   OP_DIVIDE,
+  OP_NOT,
 } OpCode;
 
 typedef struct {
diff --git a/clox/clox b/clox/clox
index e1e7feb..109e9f2 100755
Binary files a/clox/clox and b/clox/clox differ
diff --git a/clox/compiler.c b/clox/compiler.c
index 68bd0d0..aafb558 100644
--- a/clox/compiler.c
+++ b/clox/compiler.c
@@ -143,6 +143,15 @@ static void binary() {
   }
 }
 
+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 expression() {
   // What goes here?
   parsePrecedence(PREC_ASSIGNMENT);
@@ -154,7 +163,7 @@ static void grouping() {
 
 static void number() {
   double value = strtod(parser.previous.start, NULL);
-  emitConstant(value);
+  emitConstant(NUMBER_VAL(value));
 }
 
 static void unary() {
@@ -164,6 +173,7 @@ static void unary() {
   parsePrecedence(PREC_UNARY);
   // Emit the operator instruction.
   switch (operatorType) {
+    case TOKEN_BANG: emitByte(OP_NOT); break;
     case TOKEN_MINUS: emitByte(OP_NEGATE); break;
     default: return; // Unreachable.
   }
@@ -200,7 +210,7 @@ ParseRule rules[] = {
   [TOKEN_SEMICOLON]     = {NULL,     NULL,   PREC_NONE},
   [TOKEN_SLASH]         = {NULL,     binary, PREC_FACTOR},
   [TOKEN_STAR]          = {NULL,     binary, PREC_FACTOR},
-  [TOKEN_BANG]          = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_BANG]          = {unary,    NULL,   PREC_NONE},
   [TOKEN_BANG_EQUAL]    = {NULL,     NULL,   PREC_NONE},
   [TOKEN_EQUAL]         = {NULL,     NULL,   PREC_NONE},
   [TOKEN_EQUAL_EQUAL]   = {NULL,     NULL,   PREC_NONE},
@@ -214,17 +224,17 @@ ParseRule rules[] = {
   [TOKEN_AND]           = {NULL,     NULL,   PREC_NONE},
   [TOKEN_CLASS]         = {NULL,     NULL,   PREC_NONE},
   [TOKEN_ELSE]          = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_FALSE]         = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_FALSE]         = {literal,  NULL,   PREC_NONE},
   [TOKEN_FOR]           = {NULL,     NULL,   PREC_NONE},
   [TOKEN_FUN]           = {NULL,     NULL,   PREC_NONE},
   [TOKEN_IF]            = {NULL,     NULL,   PREC_NONE},
-  [TOKEN_NIL]           = {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]          = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_TRUE]          = {literal,  NULL,   PREC_NONE},
   [TOKEN_VAR]           = {NULL,     NULL,   PREC_NONE},
   [TOKEN_WHILE]         = {NULL,     NULL,   PREC_NONE},
   [TOKEN_ERROR]         = {NULL,     NULL,   PREC_NONE},
diff --git a/clox/compiler.o b/clox/compiler.o
index 7e02c78..7f30988 100644
Binary files a/clox/compiler.o and b/clox/compiler.o differ
diff --git a/clox/debug.c b/clox/debug.c
index 8f7af21..4175c21 100644
--- a/clox/debug.c
+++ b/clox/debug.c
@@ -36,6 +36,18 @@ int disassembleInstruction(Chunk* chunk, int offset) {
   switch (instruction) {
     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:
@@ -46,6 +58,8 @@ int disassembleInstruction(Chunk* chunk, int offset) {
       return simpleInstruction("OP_DIVIDE", offset);
     case OP_NEGATE:
       return simpleInstruction("OP_NEGATE", offset);
+    case OP_NOT:
+      return simpleInstruction("OP_NOT", offset);
     case OP_RETURN:
       return simpleInstruction("OP_RETURN", offset);
     default:
diff --git a/clox/debug.o b/clox/debug.o
index 84609a4..1431a55 100644
Binary files a/clox/debug.o and b/clox/debug.o differ
diff --git a/clox/value.c b/clox/value.c
index 5657f68..19b7c0b 100644
--- a/clox/value.c
+++ b/clox/value.c
@@ -24,5 +24,22 @@ void freeValueArray(ValueArray* array) {
   initValueArray(array);
 }
 void printValue(Value value) {
-  printf("%g", value);
+  switch (value.type) {
+    case VAL_BOOL:
+      printf(AS_BOOL(value) ? "true" : "false");
+      break;
+    case VAL_NIL: printf("nil"); break;
+    case VAL_NUMBER: printf("%g", AS_NUMBER(value)); break;
+  }
 }
+
+bool valuesEqual(Value a, Value b) {
+  if (a.type != b.type) return false;
+  switch (a.type) {
+    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);
+    default:         return false; // Unreachable.
+  }
+}
+
diff --git a/clox/value.h b/clox/value.h
index 86d4b1c..ee41d23 100644
--- a/clox/value.h
+++ b/clox/value.h
@@ -3,7 +3,33 @@
 
 #include "common.h"
 
-typedef double Value;
+
+//typedef double Value;
+
+typedef enum {
+  VAL_BOOL,
+  VAL_NIL, 
+  VAL_NUMBER,
+} ValueType;
+
+typedef struct {
+  ValueType type;
+  union {
+    bool boolean;
+    double number;
+  } as; 
+} 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 AS_BOOL(value)    ((value).as.boolean)
+#define AS_NUMBER(value)  ((value).as.number)
+
+#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}})
 
 typedef struct {
   int capacity;
diff --git a/clox/value.o b/clox/value.o
index 96ee556..2a9e016 100644
Binary files a/clox/value.o and b/clox/value.o differ
diff --git a/clox/vm.c b/clox/vm.c
index 9c6c687..4d4d599 100644
--- a/clox/vm.c
+++ b/clox/vm.c
@@ -1,3 +1,4 @@
+#include <stdarg.h>
 #include <stdio.h>
 #include "common.h"
 #include "compiler.h"
@@ -7,6 +8,20 @@ VM vm;
 static void resetStack() {
   vm.stackTop = vm.stack;
 }
+
+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);
+  resetStack();
+}
+
 void initVM() {
   resetStack();
 }
@@ -23,14 +38,26 @@ Value pop() {
   return *vm.stackTop;
 }
 
+static Value peek(int distance) {
+  return vm.stackTop[-1 - distance];
+}
+
+static bool isFalsey(Value value) {
+  return IS_NIL(value) || (IS_BOOL(value) && !AS_BOOL(value));
+}
+
 static InterpretResult run() {
 #define READ_BYTE() (*vm.ip++)
 #define READ_CONSTANT() (vm.chunk->constants.values[READ_BYTE()])
-#define BINARY_OP(op) \
+#define BINARY_OP(valueType, op) \
     do { \
-      double b = pop(); \
-      double a = pop(); \
-      push(a op b); \
+      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
@@ -53,11 +80,25 @@ static InterpretResult run() {
         push(constant);
         break;
       }
-      case OP_NEGATE:   push(-pop()); break;
-      case OP_ADD:      BINARY_OP(+); break;
-      case OP_SUBTRACT: BINARY_OP(-); break;
-      case OP_MULTIPLY: BINARY_OP(*); break;
-      case OP_DIVIDE:   BINARY_OP(/); 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_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;
+        }
+        push(NUMBER_VAL(-AS_NUMBER(pop())));
+        break;
       case OP_RETURN: {
         printValue(pop());
         printf("\n");
diff --git a/clox/vm.o b/clox/vm.o
index 10f26d5..287fae9 100644
Binary files a/clox/vm.o and b/clox/vm.o differ