From a443d9e3f6be9d45fb3443401d5940fb5cc67613 Mon Sep 17 00:00:00 2001
From: Yuichi Nishiwaki <yuichi.nishiwaki@gmail.com>
Date: Wed, 22 Jan 2014 20:57:05 +0900
Subject: [PATCH] add pic_list_ref and pic_list_tail

---
 include/picrin/pair.h |  3 +++
 src/pair.c            | 15 +++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/include/picrin/pair.h b/include/picrin/pair.h
index 1aed0d98..02599ff6 100644
--- a/include/picrin/pair.h
+++ b/include/picrin/pair.h
@@ -29,6 +29,9 @@ pic_value pic_cadr(pic_state *, pic_value);
 pic_value pic_cdar(pic_state *, pic_value);
 pic_value pic_cddr(pic_state *, pic_value);
 
+pic_value pic_list_tail(pic_state *, pic_value ,int);
+pic_value pic_list_ref(pic_state *, pic_value, int);
+
 #if defined(__cplusplus)
 }
 #endif
diff --git a/src/pair.c b/src/pair.c
index e6762221..ee443f68 100644
--- a/src/pair.c
+++ b/src/pair.c
@@ -180,6 +180,21 @@ pic_cddr(pic_state *pic, pic_value v)
   return pic_cdr(pic, pic_cdr(pic, v));
 }
 
+pic_value
+pic_list_tail(pic_state *pic, pic_value list, int i)
+{
+  while (i-- > 0) {
+    list = pic_cdr(pic, list);
+  }
+  return list;
+}
+
+pic_value
+pic_list_ref(pic_state *pic, pic_value list, int i)
+{
+  return pic_car(pic, pic_list_tail(pic, list, i));
+}
+
 static pic_value
 pic_pair_pair_p(pic_state *pic)
 {