rearrange builtins

builtins/push.go

@@ -0,0 +1,28 @@
+package builtins
+
+import "monkey/object"
+
+// Push ...
+func Push(args ...object.Object) object.Object {
+	if len(args) != 2 {
+		return newError("wrong number of arguments. got=%d, want=2",
+			len(args))
+	}
+	if args[0].Type() != object.ARRAY_OBJ {
+		return newError("argument to `push` must be array, got %s",
+			args[0].Type())
+	}
+
+	arr := args[0].(*object.Array)
+	length := len(arr.Elements)
+
+	newElements := make([]object.Object, length+1)
+	copy(newElements, arr.Elements)
+	if immutable, ok := args[1].(object.Immutable); ok {
+		newElements[length] = immutable.Clone()
+	} else {
+		newElements[length] = args[1]
+	}
+
+	return &object.Array{Elements: newElements}
+}