From ec3a32ef2485e1ffc905dc0080eba945ceed4349 Mon Sep 17 00:00:00 2001
From: Yuichi Nishiwaki <yuichi.nishiwaki@gmail.com>
Date: Tue, 29 Oct 2013 02:50:26 +0900
Subject: [PATCH] implement some list functions in built-in.scm

---
 piclib/built-in.scm | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/piclib/built-in.scm b/piclib/built-in.scm
index d7070353..334b412d 100644
--- a/piclib/built-in.scm
+++ b/piclib/built-in.scm
@@ -21,3 +21,29 @@
 
 (define (list . args)
   args)
+
+(define (list? obj)
+  (if (null? obj)
+      #t
+      (if (pair? obj)
+	  (list? (cdr obj))
+	  #f)))
+
+(define (length list)
+  (if (null? list)
+      0
+      (+ 1 (length (cdr list)))))
+
+(define (append xs ys)
+  (if (null? xs)
+      ys
+      (cons (car xs)
+	    (append (cdr xs) ys))))
+
+(define (list-tail list k)
+  (if (zero? k)
+      list
+      (list-tail (cdr list) (- k 1))))
+
+(define (list-ref list k)
+  (car (list-tail list k)))