From 18d143aa6239266cf3bff522289877ff817cc861 Mon Sep 17 00:00:00 2001
From: Jan Nieuwenhuizen <janneke@gnu.org>
Date: Tue, 24 Apr 2018 07:00:35 +0200
Subject: [PATCH] core: last_pair: Move to core.

* src/lib.c (last_pair): New function.
* module/mes/scm.mes (last-pair): Remove.
---
 module/mes/scm.mes | 5 -----
 src/lib.c          | 8 ++++++++
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/module/mes/scm.mes b/module/mes/scm.mes
index 23d4bf53..3aaac56d 100644
--- a/module/mes/scm.mes
+++ b/module/mes/scm.mes
@@ -157,11 +157,6 @@
   (if (= 0 n) x
       (list-tail (cdr x) (- n 1))))
 
-(define (last-pair lst)
-  (let loop ((lst lst))
-    (if (or (null? lst) (null? (cdr lst))) lst
-        (loop (cdr lst)))))
-
 (define (iota n)
   (if (<= n 0) '()
       (append2 (iota (- n 1)) (list (- n 1)))))
diff --git a/src/lib.c b/src/lib.c
index 7b028d5d..18045908 100644
--- a/src/lib.c
+++ b/src/lib.c
@@ -331,3 +331,11 @@ equal2_p (SCM a, SCM b)
     }
   return eq_p (a, b);
 }
+
+SCM
+last_pair (SCM x)
+{
+  while (x != cell_nil && CDR (x) != cell_nil)
+    x = CDR (x);
+  return x;
+}