clone

evaluator/evaluator.go

@@ -70,7 +70,12 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 		if isError(val) {
 			return val
 		}
-		env.Set(node.Name.Value, val)
+
+		if mutable, ok := val.(object.Mutable); ok {
+			env.Set(node.Name.Value, mutable.Clone())
+		} else {
+			env.Set(node.Name.Value, val)
+		}
 
 	case *ast.Identifier:
 		return evalIdentifier(node, env)