Extra Features

compiler/compiler.go

@@ -75,7 +75,10 @@ func (c *Compiler) Compile(node ast.Node) error {
 		if err != nil {
 			return err
 		}
-		c.emit(code.OpPop)
+
+		if !c.lastInstructionIs(code.OpNoop) {
+			c.emit(code.OpPop)
+		}
 
 	case *ast.InfixExpression:
 		if node.Operator == "<" {
@@ -196,7 +199,11 @@ func (c *Compiler) Compile(node ast.Node) error {
 		}
 
 	case *ast.LetStatement:
-		symbol := c.symbolTable.Define(node.Name.Value)
+		symbol, ok := c.symbolTable.Resolve(node.Name.Value)
+		if !ok {
+			symbol = c.symbolTable.Define(node.Name.Value)
+		}
+
 		err := c.Compile(node.Value)
 		if err != nil {
 			return err
@@ -328,6 +335,27 @@ func (c *Compiler) Compile(node ast.Node) error {
 
 		c.emit(code.OpCall, len(node.Arguments))
 
+	case *ast.WhileExpression:
+		jumpConditionPos := len(c.currentInstructions())
+
+		err := c.Compile(node.Condition)
+		if err != nil {
+			return err
+		}
+
+		// Emit an `OpJump`with a bogus value
+		jumpIfFalsePos := c.emit(code.OpJumpNotTruthy, 0xFFFF)
+
+		err = c.Compile(node.Consequence)
+		if err != nil {
+			return err
+		}
+
+		c.emit(code.OpJump, jumpConditionPos)
+
+		afterConsequencePos := c.emit(code.OpNoop)
+		c.changeOperand(jumpIfFalsePos, afterConsequencePos)
+
 	}
 
 	return nil