Change assignment into expressions

vm/vm.go

@@ -186,6 +186,11 @@ func (vm *VM) Run() error {
 			vm.currentFrame().ip += 2
 			vm.globals[globalIndex] = vm.pop()
 
+			err := vm.push(Null)
+			if err != nil {
+				return err
+			}
+
 		case code.OpAssignLocal:
 			localIndex := code.ReadUint8(ins[ip+1:])
 			vm.currentFrame().ip += 1
@@ -193,6 +198,11 @@ func (vm *VM) Run() error {
 			frame := vm.currentFrame()
 			vm.stack[frame.basePointer+int(localIndex)] = vm.pop()
 
+			err := vm.push(Null)
+			if err != nil {
+				return err
+			}
+
 		case code.OpGetGlobal:
 			globalIndex := code.ReadUint16(ins[ip+1:])
 			vm.currentFrame().ip += 2
@@ -229,11 +239,21 @@ func (vm *VM) Run() error {
 				return err
 			}
 
-		case code.OpIndex:
+		case code.OpSetItem:
+			value := vm.pop()
 			index := vm.pop()
 			left := vm.pop()
 
-			err := vm.executeIndexExpressions(left, index)
+			err := vm.executeSetItem(left, index, value)
+			if err != nil {
+				return err
+			}
+
+		case code.OpGetItem:
+			index := vm.pop()
+			left := vm.pop()
+
+			err := vm.executeGetItem(left, index)
 			if err != nil {
 				return err
 			}
@@ -328,20 +348,39 @@ func (vm *VM) Run() error {
 	return nil
 }
 
-func (vm *VM) executeIndexExpressions(left, index object.Object) error {
+func (vm *VM) executeSetItem(left, index, value object.Object) error {
 	switch {
-	case left.Type() == object.STRING_OBJ && index.Type() == object.INTEGER_OBJ:
-		return vm.executeStringIndex(left, index)
 	case left.Type() == object.ARRAY_OBJ && index.Type() == object.INTEGER_OBJ:
-		return vm.executeArrayIndex(left, index)
+		return vm.executeArraySetItem(left, index, value)
 	case left.Type() == object.HASH_OBJ:
-		return vm.executeHashIndex(left, index)
+		return vm.executeHashSetItem(left, index, value)
 	default:
-		return fmt.Errorf("index operator not supported: %s", left.Type())
+		return fmt.Errorf(
+			"set item operation not supported: left=%s index=%s",
+			left.Type(), index.Type(),
+		)
 	}
 }
 
-func (vm *VM) executeArrayIndex(array, index object.Object) error {
+func (vm *VM) executeGetItem(left, index object.Object) error {
+	switch {
+	case left.Type() == object.STRING_OBJ && index.Type() == object.INTEGER_OBJ:
+		return vm.executeStringGetItem(left, index)
+	case left.Type() == object.STRING_OBJ && index.Type() == object.STRING_OBJ:
+		return vm.executeStringIndex(left, index)
+	case left.Type() == object.ARRAY_OBJ && index.Type() == object.INTEGER_OBJ:
+		return vm.executeArrayGetItem(left, index)
+	case left.Type() == object.HASH_OBJ:
+		return vm.executeHashGetItem(left, index)
+	default:
+		return fmt.Errorf(
+			"index operator not supported: left=%s index=%s",
+			left.Type(), index.Type(),
+		)
+	}
+}
+
+func (vm *VM) executeArrayGetItem(array, index object.Object) error {
 	arrayObject := array.(*object.Array)
 	i := index.(*object.Integer).Value
 	max := int64(len(arrayObject.Elements) - 1)
@@ -353,7 +392,20 @@ func (vm *VM) executeArrayIndex(array, index object.Object) error {
 	return vm.push(arrayObject.Elements[i])
 }
 
-func (vm *VM) executeHashIndex(hash, index object.Object) error {
+func (vm *VM) executeArraySetItem(array, index, value object.Object) error {
+	arrayObject := array.(*object.Array)
+	i := index.(*object.Integer).Value
+	max := int64(len(arrayObject.Elements) - 1)
+
+	if i < 0 || i > max {
+		return fmt.Errorf("index out of bounds: %d", i)
+	}
+
+	arrayObject.Elements[i] = value
+	return vm.push(Null)
+}
+
+func (vm *VM) executeHashGetItem(hash, index object.Object) error {
 	hashObject := hash.(*object.Hash)
 
 	key, ok := index.(object.Hashable)
@@ -369,6 +421,20 @@ func (vm *VM) executeHashIndex(hash, index object.Object) error {
 	return vm.push(pair.Value)
 }
 
+func (vm *VM) executeHashSetItem(hash, index, value object.Object) error {
+	hashObject := hash.(*object.Hash)
+
+	key, ok := index.(object.Hashable)
+	if !ok {
+		return fmt.Errorf("unusable as hash key: %s", index.Type())
+	}
+
+	hashed := key.HashKey()
+	hashObject.Pairs[hashed] = object.HashPair{Key: index, Value: value}
+
+	return vm.push(Null)
+}
+
 func (vm *VM) buildHash(startIndex, endIndex int) (object.Object, error) {
 	hashedPairs := make(map[object.HashKey]object.HashPair)
 
@@ -621,7 +687,7 @@ func (vm *VM) pushClosure(constIndex, numFree int) error {
 	return vm.push(closure)
 }
 
-func (vm *VM) executeStringIndex(str, index object.Object) error {
+func (vm *VM) executeStringGetItem(str, index object.Object) error {
 	stringObject := str.(*object.String)
 	i := index.(*object.Integer).Value
 	max := int64(len(stringObject.Value) - 1)
@@ -633,6 +699,17 @@ func (vm *VM) executeStringIndex(str, index object.Object) error {
 	return vm.push(&object.String{Value: string(stringObject.Value[i])})
 }
 
+func (vm *VM) executeStringIndex(str, index object.Object) error {
+	stringObject := str.(*object.String)
+	substr := index.(*object.String).Value
+
+	return vm.push(
+		&object.Integer{
+			Value: int64(strings.Index(stringObject.Value, substr)),
+		},
+	)
+}
+
 func (vm *VM) executeStringComparison(op code.Opcode, left, right object.Object) error {
 	leftValue := left.(*object.String).Value
 	rightValue := right.(*object.String).Value