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)

evaluator/evaluator_test.go

@@ -251,6 +251,7 @@ func TestAssignmentStatements(t *testing.T) {
 		{"let a = 0; a = 5; let b = 0; b = a; b;", 5},
 		{"let a = 0; a = 5; let b = 0; b = a; let c = 0; c = a + b + 5;", 15},
 		{"let a = 0; a = 5; let b = 0; b = a; let c = 0; c = a + b + 5; c;", 15},
+		{"let a = 5; let b = a; a = 0; b;", 5},
 	}
 
 	for _, tt := range tests {
@@ -474,6 +475,7 @@ func TestArrayIndexExpressions(t *testing.T) {
 	}
 
 	for _, tt := range tests {
+		t.Log(tt.input)
 		evaluated := testEval(tt.input)
 
 		integer, ok := tt.expected.(int)