Chapter 21

clox/src/chunk.h

@@ -12,6 +12,7 @@ typedef enum {
   OP_POP,
   OP_GET_GLOBAL,
   OP_DEFINE_GLOBAL,
+  OP_SET_GLOBAL,
   OP_EQUAL,
   OP_GREATER,
   OP_LESS,

clox/src/compiler.c

@@ -30,7 +30,7 @@ typedef enum {
   PREC_PRIMARY
 } Precedence;
 
-typedef void (*ParseFn)();
+typedef void (*ParseFn)(bool canAssign);
 
 typedef struct {
   ParseFn prefix;
@@ -140,7 +140,7 @@ static uint8_t parseVariable(const char *name);
 static void defineVariable(uint8_t global);
 static uint8_t identifierConstant(Token *name);
 
-static void binary() {
+static void binary(bool canAssign) {
   TokenType operatorType = parser.previous.type;
   ParseRule *rule = getRule(operatorType);
   parsePrecedence((Precedence)(rule->precedence + 1));
@@ -181,7 +181,7 @@ static void binary() {
   }
 }
 
-static void literal() {
+static void literal(bool canAssign) {
   switch (parser.previous.type) {
   case TOKEN_FALSE:
     emitByte(OP_FALSE);
@@ -267,26 +267,32 @@ static void statement() {
   }
 }
 
-static void number() {
+static void number(bool canAssign) {
   double value = strtod(parser.previous.start, NULL);
   emitConstant(NUMBER_VAL(value));
 }
 
-static void string() {
+static void string(bool canAssign) {
   emitConstant(OBJ_VAL(
       copyString(parser.previous.start + 1, parser.previous.length - 2)));
 }
 
-static void namedVariable(Token name) {
+static void namedVariable(Token name, bool canAssign) {
   uint8_t arg = identifierConstant(&name);
-  emitBytes(OP_GET_GLOBAL, arg);
+
+  if (canAssign && match(TOKEN_EQUAL)) {
+    expression();
+    emitBytes(OP_SET_GLOBAL, arg);
+  } else {
+    emitBytes(OP_GET_GLOBAL, arg);
+  }
 }
 
-static void variable() {
-  namedVariable(parser.previous);
+static void variable(bool canAssign) {
+  namedVariable(parser.previous, canAssign);
 }
 
-static void unary() {
+static void unary(bool canAssign) {
   TokenType operatorType = parser.previous.type;
 
   // Compile the operand.
@@ -305,7 +311,7 @@ static void unary() {
   }
 }
 
-static void grouping() {
+static void grouping(bool canAssign) {
   expression();
   consume(TOKEN_RIGHT_PAREN, "Expect ')' after expression.");
 }
@@ -361,12 +367,17 @@ 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.");
   }
 }
 

clox/src/debug.c

@@ -48,6 +48,8 @@ int disassembleInstruction(Chunk *chunk, int offset) {
     return constantInstruction("OP_GET_GLOBAL", chunk, offset);
   case OP_DEFINE_GLOBAL:
     return constantInstruction("OP_DEFINE_GLOBAL", chunk, offset);
+  case OP_SET_GLOBAL:
+    return constantInstruction("OP_SET_GLOBAL", chunk, offset);
   case OP_EQUAL:
     return simpleInstruction("OP_EQUAL", offset);
   case OP_GREATER:

clox/src/vm.c

@@ -119,8 +119,8 @@ static InterpretResult run() {
       ObjString *name = READ_STRING();
       Value value;
       if (!tableGet(&vm.globals, name, &value)) {
-	runtimeError("Undefined variable '%s'.", name->chars);
-	return INTERPRET_RUNTIME_ERROR;
+        runtimeError("Undefined variable '%s'.", name->chars);
+        return INTERPRET_RUNTIME_ERROR;
       }
       push(value);
       break;
@@ -131,6 +131,15 @@ static InterpretResult run() {
       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_EQUAL: {
       Value b = pop();
       Value a = pop();