From 5dba94ed1eec7a808cab022a23480b4d39518307 Mon Sep 17 00:00:00 2001
From: Teddy <ted.sybil@gmail.com>
Date: Mon, 5 Aug 2013 10:14:07 +0800
Subject: empty-list fix

---
 builtin.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/builtin.cpp b/builtin.cpp
index 17c5e94..79ecdfb 100644
--- a/builtin.cpp
+++ b/builtin.cpp
@@ -280,7 +280,7 @@ EvalObj *builtin_car(ArgList *args) {
     if (args == empty_list ||
         args->cdr != empty_list)
         throw TokenError("car", RUN_ERR_WRONG_NUM_OF_ARGS);
-    if (!args->car->is_cons_obj())
+    if (args->car == empty_list || !args->car->is_cons_obj())
         throw TokenError("pair", RUN_ERR_WRONG_TYPE);
 
     return TO_CONS(args->car)->car;
@@ -290,7 +290,7 @@ EvalObj *builtin_cdr(ArgList *args) {
     if (args == empty_list ||
         args->cdr != empty_list)
         throw TokenError("cdr", RUN_ERR_WRONG_NUM_OF_ARGS);
-    if (!args->car->is_cons_obj())
+    if (args->car == empty_list || !args->car->is_cons_obj())
         throw TokenError("pair", RUN_ERR_WRONG_TYPE);
 
     return TO_CONS(args->car)->cdr;
-- 
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