From 293fef52359ed3691dd707392df53359c5969e5f Mon Sep 17 00:00:00 2001
From: Yuichi Nishiwaki <yuichi.nishiwaki@gmail.com>
Date: Mon, 20 Jan 2014 16:43:54 +0900
Subject: [PATCH] add pic_list_ref

---
 include/picrin/pair.h | 2 ++
 src/pair.c            | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/include/picrin/pair.h b/include/picrin/pair.h
index 1aed0d98..e42a041a 100644
--- a/include/picrin/pair.h
+++ b/include/picrin/pair.h
@@ -29,6 +29,8 @@ 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_ref(pic_state *, pic_value, int);
+
 #if defined(__cplusplus)
 }
 #endif
diff --git a/src/pair.c b/src/pair.c
index e6762221..b597e64f 100644
--- a/src/pair.c
+++ b/src/pair.c
@@ -180,6 +180,15 @@ pic_cddr(pic_state *pic, pic_value v)
   return pic_cdr(pic, pic_cdr(pic, v));
 }
 
+pic_value
+pic_list_ref(pic_state *pic, pic_value list, int i)
+{
+  while (i-- > 0) {
+    list = pic_cdr(pic, list);
+  }
+  return pic_car(pic, list);
+}
+
 static pic_value
 pic_pair_pair_p(pic_state *pic)
 {