Extra Features

evaluator/evaluator.go

@@ -35,6 +35,9 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 	case *ast.IfExpression:
 		return evalIfExpression(node, env)
 
+	case *ast.WhileExpression:
+		return evalWhileExpression(node, env)
+
 	case *ast.ReturnStatement:
 		val := Eval(node.ReturnValue, env)
 		if isError(val) {
@@ -123,6 +126,29 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 	return nil
 }
 
+func evalWhileExpression(we *ast.WhileExpression, env *object.Environment) object.Object {
+	var result object.Object
+
+	for {
+		condition := Eval(we.Condition, env)
+		if isError(condition) {
+			return condition
+		}
+
+		if isTruthy(condition) {
+			result = Eval(we.Consequence, env)
+		} else {
+			break
+		}
+	}
+
+	if result != nil {
+		return result
+	} else {
+		return NULL
+	}
+}
+
 func evalProgram(program *ast.Program, env *object.Environment) object.Object {
 	var result object.Object