Local variables.

example/hello.wren

@@ -1,2 +1,3 @@
-123.ok
-123.yar
+var a = 123
+var b = 345
+a

src/compiler.c

@@ -76,6 +76,9 @@ typedef struct
   Block* block;
   int numCodes;
 
+  // Symbol table for declared local variables in the current block.
+  SymbolTable locals;
+
   // Non-zero if a compile error has occurred.
   int hasError;
 } Compiler;
@@ -105,6 +108,7 @@ static char peekChar(Compiler* compiler);
 static void makeToken(Compiler* compiler, TokenType type);
 
 // Utility:
+static void emit(Compiler* compiler, Code code);
 static void error(Compiler* compiler, const char* format, ...);
 
 Block* compile(VM* vm, const char* source, size_t sourceLength)
@@ -118,7 +122,14 @@ Block* compile(VM* vm, const char* source, size_t sourceLength)
   compiler.tokenStart = 0;
   compiler.currentChar = 0;
 
-  // TODO(bob): Zero-init current token.
+  initSymbolTable(&compiler.locals);
+
+  // Zero-init the current token. This will get copied to previous when
+  // advance() is called below.
+  compiler.current.type = TOKEN_EOF;
+  compiler.current.start = 0;
+  compiler.current.end = 0;
+
   // Read the first token.
   advance(&compiler);
 
@@ -132,37 +143,47 @@ Block* compile(VM* vm, const char* source, size_t sourceLength)
 
   compiler.numCodes = 0;
 
-  do
+  for (;;)
   {
     statement(&compiler);
-    // TODO(bob): Discard previous value.
-  } while (!match(&compiler, TOKEN_EOF));
 
-  compiler.block->bytecode[compiler.numCodes++] = CODE_END;
+    if (match(&compiler, TOKEN_EOF)) break;
+
+    // Discard the result of the previous expression.
+    emit(&compiler, CODE_POP);
+  }
+
+  emit(&compiler, CODE_END);
+
+  compiler.block->numLocals = compiler.locals.count;
 
   return compiler.hasError ? NULL : compiler.block;
 }
 
 void statement(Compiler* compiler)
 {
-  /*
   if (match(compiler, TOKEN_VAR))
   {
-    Token* name = consume(compiler, TOKEN_NAME);
-    Node* initializer = NULL;
-    if (match(compiler, TOKEN_EQ))
-    {
-      initializer = expression(parser);
-    }
-    if (peek(parser) != TOKEN_OUTDENT) consume(compiler, TOKEN_LINE);
+    consume(compiler, TOKEN_NAME);
+    int local = addSymbol(&compiler->locals,
+        compiler->source + compiler->previous.start,
+        compiler->previous.end - compiler->previous.start);
 
-    NodeVar* node = malloc(sizeof(NodeVar));
-    node->node.type = NODE_VAR;
-    node->name = name;
-    node->initializer = initializer;
-    return (Node*)node;
+    if (local == -1)
+    {
+      error(compiler, "Local variable is already defined.");
+    }
+
+    // TODO(bob): Allow uninitialized vars?
+    consume(compiler, TOKEN_EQ);
+
+    // Compile the initializer.
+    expression(compiler);
+
+    emit(compiler, CODE_STORE_LOCAL);
+    emit(compiler, local);
+    return;
   }
-  */
 
   // Statement expression.
   expression(compiler);
@@ -186,23 +207,38 @@ void call(Compiler* compiler)
   if (match(compiler, TOKEN_DOT))
   {
     consume(compiler, TOKEN_NAME);
-    int symbol = getSymbol(compiler->vm,
-                           compiler->source + compiler->previous.start,
-                           compiler->previous.end - compiler->previous.start);
-    printf("symbol %d\n", symbol);
-
+    int symbol = ensureSymbol(&compiler->vm->symbols,
+        compiler->source + compiler->previous.start,
+        compiler->previous.end - compiler->previous.start);
 
     // Compile the method call.
-    compiler->block->bytecode[compiler->numCodes++] = CODE_CALL;
-    compiler->block->bytecode[compiler->numCodes++] = symbol;
+    emit(compiler, CODE_CALL);
+    emit(compiler, symbol);
   }
 }
 
 void primary(Compiler* compiler)
 {
+  if (match(compiler, TOKEN_NAME))
+  {
+    int local = findSymbol(&compiler->locals,
+        compiler->source + compiler->previous.start,
+        compiler->previous.end - compiler->previous.start);
+    if (local == -1)
+    {
+      // TODO(bob): Look for globals or names in outer scopes.
+      error(compiler, "Unknown variable.");
+    }
+
+    emit(compiler, CODE_LOAD_LOCAL);
+    emit(compiler, local);
+    return;
+  }
+
   if (match(compiler, TOKEN_NUMBER))
   {
     number(compiler, &compiler->previous);
+    return;
   }
 }
 
@@ -219,18 +255,14 @@ void number(Compiler* compiler, Token* token)
 
   // Define a constant for the literal.
   // TODO(bob): See if constant with same value already exists.
-  Value constant = malloc(sizeof(Obj));
-  constant->type = OBJ_INT;
-  constant->flags = 0;
-
   // TODO(bob): Handle truncation!
-  constant->value = (int)value;
+  Value constant = makeNum((int)value);
 
   compiler->block->constants[compiler->block->numConstants++] = constant;
 
   // Compile the code to load the constant.
-  compiler->block->bytecode[compiler->numCodes++] = CODE_CONSTANT;
-  compiler->block->bytecode[compiler->numCodes++] = compiler->block->numConstants - 1;
+  emit(compiler, CODE_CONSTANT);
+  emit(compiler, compiler->block->numConstants - 1);
 }
 
 TokenType peek(Compiler* compiler)
@@ -286,7 +318,17 @@ void readNextToken(Compiler* compiler)
       case '/': makeToken(compiler, TOKEN_SLASH); return;
       case '%': makeToken(compiler, TOKEN_PERCENT); return;
       case '+': makeToken(compiler, TOKEN_PLUS); return;
-      case '-': makeToken(compiler, TOKEN_MINUS); return;
+      case '-':
+        if (isDigit(peekChar(compiler)))
+        {
+          readNumber(compiler);
+        }
+        else
+        {
+          makeToken(compiler, TOKEN_MINUS);
+        }
+        return;
+
       case '|': makeToken(compiler, TOKEN_PIPE); return;
       case '&': makeToken(compiler, TOKEN_AMP); return;
       case '=':
@@ -434,6 +476,11 @@ void makeToken(Compiler* compiler, TokenType type)
   compiler->current.end = compiler->currentChar;
 }
 
+void emit(Compiler* compiler, Code code)
+{
+  compiler->block->bytecode[compiler->numCodes++] = code;
+}
+
 void error(Compiler* compiler, const char* format, ...)
 {
   compiler->hasError = 1;

src/vm.c

@@ -4,68 +4,194 @@
 
 #include "vm.h"
 
+typedef struct
+{
+  // Index of the current (really next-to-be-executed) instruction in the
+  // block's bytecode.
+  int ip;
+
+  // The block being executed.
+  Block* block;
+
+  // Index of the stack slot that contains the first local for this block.
+  int locals;
+} CallFrame;
+
 typedef struct
 {
   Value stack[STACK_SIZE];
   int stackSize;
+
+  CallFrame frames[MAX_CALL_FRAMES];
+  int numFrames;
 } Fiber;
 
+static void callBlock(Fiber* fiber, Block* block, int locals);
+static void push(Fiber* fiber, Value value);
 static Value pop(Fiber* fiber);
+static Value primitiveNumAbs(Value number);
 
 VM* newVM()
 {
   VM* vm = malloc(sizeof(VM));
-  vm->numSymbols = 0;
+  initSymbolTable(&vm->symbols);
+
+  for (int i = 0; i < MAX_SYMBOLS; i++)
+  {
+    vm->numClass.methods[i] = NULL;
+  }
+
+  vm->numClass.methods[ensureSymbol(&vm->symbols, "abs", 3)] = primitiveNumAbs;
 
   return vm;
 }
 
 void freeVM(VM* vm)
 {
+  clearSymbolTable(&vm->symbols);
   free(vm);
 }
 
-int getSymbol(VM* vm, const char* name, size_t length)
+Value makeNum(int number)
+{
+  Value value = malloc(sizeof(Obj));
+  value->type = OBJ_INT;
+  value->flags = 0;
+  value->value = number;
+
+  return value;
+}
+
+void initSymbolTable(SymbolTable* symbols)
+{
+  symbols->count = 0;
+}
+
+void clearSymbolTable(SymbolTable* symbols)
+{
+  for (int i = 0; i < symbols->count; i++)
+  {
+    free(symbols->names[i]);
+  }
+}
+
+int addSymbolUnchecked(SymbolTable* symbols, const char* name, size_t length)
+{
+  symbols->names[symbols->count] = malloc(length + 1);
+  strncpy(symbols->names[symbols->count], name, length);
+  symbols->names[symbols->count][length] = '\0';
+
+  return symbols->count++;
+}
+
+int addSymbol(SymbolTable* symbols, const char* name, size_t length)
+{
+  // If already present, return an error.
+  if (findSymbol(symbols, name, length) != -1) return -1;
+
+  return addSymbolUnchecked(symbols, name, length);
+}
+
+int ensureSymbol(SymbolTable* symbols, const char* name, size_t length)
+{
+  // See if the symbol is already defined.
+  int existing = findSymbol(symbols, name, length);
+  if (existing != -1) return existing;
+
+  // New symbol, so add it.
+  return addSymbolUnchecked(symbols, name, length);
+}
+
+int findSymbol(SymbolTable* symbols, const char* name, size_t length)
 {
   // See if the symbol is already defined.
   // TODO(bob): O(n). Do something better.
-  for (int i = 0; i < vm->numSymbols; i++)
+  for (int i = 0; i < symbols->count; i++)
   {
-    if (strncmp(vm->symbols[i], name, length) == 0) return i;
+    if (strlen(symbols->names[i]) == length &&
+        strncmp(symbols->names[i], name, length) == 0) return i;
   }
 
-  // New symbol, so add it.
-  vm->symbols[vm->numSymbols] = malloc(length);
-  strncpy(vm->symbols[vm->numSymbols], name, length);
-  return vm->numSymbols++;
+  return -1;
 }
 
 Value interpret(VM* vm, Block* block)
 {
   Fiber fiber;
   fiber.stackSize = 0;
+  fiber.numFrames = 0;
+
+  callBlock(&fiber, block, 0);
 
-  int ip = 0;
   for (;;)
   {
-    switch (block->bytecode[ip++])
+    CallFrame* frame = &fiber.frames[fiber.numFrames - 1];
+
+    switch (frame->block->bytecode[frame->ip++])
     {
       case CODE_CONSTANT:
       {
-        Value value = block->constants[block->bytecode[ip++]];
+        int constant = frame->block->bytecode[frame->ip++];
+        Value value = frame->block->constants[constant];
         fiber.stack[fiber.stackSize++] = value;
         break;
       }
 
+      case CODE_LOAD_LOCAL:
+      {
+        int local = frame->block->bytecode[frame->ip++];
+        push(&fiber, fiber.stack[frame->locals + local]);
+        break;
+      }
+
+      case CODE_STORE_LOCAL:
+      {
+        int local = frame->block->bytecode[frame->ip++];
+        fiber.stack[frame->locals + local] = pop(&fiber);
+        break;
+      }
+
+      case CODE_POP:
+        pop(&fiber);
+        break;
+
       case CODE_CALL:
       {
-        int symbol = block->bytecode[ip++];
-        printf("call %d\n", symbol);
+        Value receiver = pop(&fiber);
+        // TODO(bob): Arguments.
+
+        int symbol = frame->block->bytecode[frame->ip++];
+
+        // TODO(bob): Support classes for other object types.
+        Class* classObj = &vm->numClass;
+
+        Primitive primitive = classObj->methods[symbol];
+        if (primitive)
+        {
+          Value result = primitive(receiver);
+          push(&fiber, result);
+        }
+        else
+        {
+          // TODO(bob): Should return nil or suspend fiber or something.
+          printf("No method.\n");
+          exit(1);
+        }
         break;
       }
 
       case CODE_END:
-        return pop(&fiber);
+      {
+        Value result = pop(&fiber);
+        fiber.numFrames--;
+
+        // If we are returning from the top-level block, just return the value.
+        if (fiber.numFrames == 0) return result;
+
+        // Store the result of the block in the first slot, which is where the
+        // caller expects it.
+        fiber.stack[frame->locals] = result;
+      }
     }
   }
 }
@@ -80,7 +206,29 @@ void printValue(Value value)
   }
 }
 
+void callBlock(Fiber* fiber, Block* block, int locals)
+{
+  fiber->frames[fiber->numFrames].block = block;
+  fiber->frames[fiber->numFrames].ip = 0;
+  fiber->frames[fiber->numFrames].locals = locals;
+  fiber->numFrames++;
+}
+
+void push(Fiber* fiber, Value value)
+{
+  // TODO(bob): Check for stack overflow.
+  fiber->stack[fiber->stackSize++] = value;
+}
+
 Value pop(Fiber* fiber)
 {
   return fiber->stack[--fiber->stackSize];
 }
+
+Value primitiveNumAbs(Value number)
+{
+  int value = number->value;
+  if (value < 0) value = -value;
+
+  return makeNum(value);
+}

src/vm.h

@@ -1,8 +1,10 @@
 #ifndef wren_vm_h
 #define wren_vm_h
 
-// TODO(bob): Make this externally controllable.
+// TODO(bob): Make these externally controllable.
 #define STACK_SIZE 1024
+#define MAX_CALL_FRAMES 256
+
 
 typedef enum {
   OBJ_INT
@@ -31,6 +33,15 @@ typedef enum
   CODE_CONSTANT,
   // Load the constant at index [arg].
 
+  CODE_POP,
+  // Pop and discard the top of stack.
+
+  CODE_LOAD_LOCAL,
+  // Pushes the value in local slot [arg]. 
+
+  CODE_STORE_LOCAL,
+  // Pops and stores the value in local slot [arg].
+
   CODE_CALL,
   // Invoke the method with symbol [arg].
 
@@ -44,22 +55,54 @@ typedef struct
   unsigned char* bytecode;
   Value* constants;
   int numConstants;
+  int numLocals;
 } Block;
 
 #define MAX_SYMBOLS 256
 
+typedef Value (*Primitive)(Value receiver);
+
 typedef struct
 {
   // TODO(bob): Make this dynamically sized.
-  char* symbols[MAX_SYMBOLS];
-  int numSymbols;
+  char* names[MAX_SYMBOLS];
+  int count;
+} SymbolTable;
 
+typedef struct
+{
+  // TODO(bob): Hack. Probably don't want to use this much space.
+  Primitive methods[MAX_SYMBOLS];
+} Class;
+
+typedef struct
+{
+  SymbolTable symbols;
+  Class numClass;
 } VM;
 
 VM* newVM();
 void freeVM(VM* vm);
 
-int getSymbol(VM* vm, const char* name, size_t length);
+Value makeNum(int number);
+
+// Initializes the symbol table.
+void initSymbolTable(SymbolTable* symbols);
+
+// Frees all dynamically allocated memory used by the symbol table, but not the
+// SymbolTable itself.
+void clearSymbolTable(SymbolTable* symbols);
+
+// Adds name to the symbol table. Returns the index of it in the table. Returns
+// -1 if the symbol is already present.
+int addSymbol(SymbolTable* symbols, const char* name, size_t length);
+
+// Adds name to the symbol table. Returns the index of it in the table. Will
+// use an existing symbol if already present.
+int ensureSymbol(SymbolTable* symbols, const char* name, size_t length);
+
+// Looks up name in the symbol table. Returns its index if found or -1 if not.
+int findSymbol(SymbolTable* symbols, const char* name, size_t length);
 
 Value interpret(VM* vm, Block* block);