From 0585569fd3754995ef1196959978911c3e4510b5 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Tue, 18 Jul 2017 06:25:31 -0700
Subject: new function: nth

Just the ANSI CL nth for lists.

* eval.c (eval_init): Register nth intrinsic.

* lib.c (nth): New function.

* lib.h (nth): Declared.

* share/txr/stdlib/place.tl (nth): New place macro,
trivially takes care of making nth an accessor.
Place macros are terrific!

* txr.1: Documented.
---
 share/txr/stdlib/place.tl | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'share')

diff --git a/share/txr/stdlib/place.tl b/share/txr/stdlib/place.tl
index 5b22e589..f8bbd580 100644
--- a/share/txr/stdlib/place.tl
+++ b/share/txr/stdlib/place.tl
@@ -972,3 +972,6 @@
     (have-n
      ^(sub ,obj 0 (- (max ,n 0))))
     (t ^(sub ,obj 0 -1))))
+
+(define-place-macro nth (index obj)
+  ^(car (nthcdr ,index ,obj)))
-- 
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