From d52f0bde95daa57f56ca61e42d732aa052704f6e Mon Sep 17 00:00:00 2001
From: Kevin Ryde <user42@zip.com.au>
Date: Sun, 28 May 2006 00:09:17 +0000
Subject: [PATCH] (append-reverse, append-reverse!): Rewrite in C.

---
 srfi/srfi-1.c   | 59 +++++++++++++++++++++++++++++++++++++++++++++++++
 srfi/srfi-1.h   |  2 ++
 srfi/srfi-1.scm |  9 --------
 3 files changed, 61 insertions(+), 9 deletions(-)

diff --git a/srfi/srfi-1.c b/srfi/srfi-1.c
index c2d9b4e71..8e27ab4e6 100644
--- a/srfi/srfi-1.c
+++ b/srfi/srfi-1.c
@@ -124,6 +124,65 @@ SCM_DEFINE (scm_srfi1_alist_copy, "alist-copy", 1, 0, 0,
 #undef FUNC_NAME
 
 
+
+SCM_DEFINE (scm_srfi1_append_reverse, "append-reverse", 2, 0, 0,
+            (SCM revhead, SCM tail),
+	    "Reverse @var{rev-head}, append @var{tail} to it, and return the\n"
+	    "result.  This is equivalent to @code{(append (reverse\n"
+	    "@var{rev-head}) @var{tail})}, but its implementation is more\n"
+	    "efficient.\n"
+	    "\n"
+	    "@example\n"
+	    "(append-reverse '(1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6)\n"
+	    "@end example")
+#define FUNC_NAME s_scm_srfi1_append_reverse
+{
+  while (scm_is_pair (revhead))
+    {
+      /* copy first element of revhead onto front of tail */
+      tail = scm_cons (SCM_CAR (revhead), tail);
+      revhead = SCM_CDR (revhead);
+    }
+  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (revhead), revhead, SCM_ARG1, FUNC_NAME,
+                   "list");
+  return tail;
+}
+#undef FUNC_NAME
+
+
+SCM_DEFINE (scm_srfi1_append_reverse_x, "append-reverse!", 2, 0, 0,
+            (SCM revhead, SCM tail),
+	    "Reverse @var{rev-head}, append @var{tail} to it, and return the\n"
+	    "result.  This is equivalent to @code{(append! (reverse!\n"
+	    "@var{rev-head}) @var{tail})}, but its implementation is more\n"
+	    "efficient.\n"
+	    "\n"
+	    "@example\n"
+	    "(append-reverse! (list 1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6)\n"
+	    "@end example\n"
+	    "\n"
+	    "@var{rev-head} may be modified in order to produce the result.")
+#define FUNC_NAME s_scm_srfi1_append_reverse_x
+{
+  SCM newtail;
+
+  while (scm_is_pair (revhead))
+    {
+      /* take the first cons cell from revhead */
+      newtail = revhead;
+      revhead = SCM_CDR (revhead);
+
+      /* make it the new start of tail, appending the previous */
+      SCM_SETCDR (newtail, tail);
+      tail = newtail;
+    }
+  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (revhead), revhead, SCM_ARG1, FUNC_NAME,
+                   "list");
+  return tail;
+}
+#undef FUNC_NAME
+
+
 SCM_DEFINE (scm_srfi1_break, "break", 2, 0, 0,
             (SCM pred, SCM lst),
 	    "Return two values, the longest initial prefix of @var{lst}\n"
diff --git a/srfi/srfi-1.h b/srfi/srfi-1.h
index 810f1046d..936586697 100644
--- a/srfi/srfi-1.h
+++ b/srfi/srfi-1.h
@@ -33,6 +33,8 @@
 #endif
 
 SCM_SRFI1_API SCM scm_srfi1_alist_copy (SCM alist);
+SCM_SRFI1_API SCM scm_srfi1_append_reverse (SCM revhead, SCM tail);
+SCM_SRFI1_API SCM scm_srfi1_append_reverse_x (SCM revhead, SCM tail);
 SCM_SRFI1_API SCM scm_srfi1_break (SCM pred, SCM lst);
 SCM_SRFI1_API SCM scm_srfi1_break_x (SCM pred, SCM lst);
 SCM_SRFI1_API SCM scm_srfi1_car_plus_cdr (SCM pair);
diff --git a/srfi/srfi-1.scm b/srfi/srfi-1.scm
index 30e536f5d..a7876b711 100644
--- a/srfi/srfi-1.scm
+++ b/srfi/srfi-1.scm
@@ -324,15 +324,6 @@
 
 ;;; Miscelleneous: length, append, concatenate, reverse, zip & count
 
-(define (append-reverse rev-head tail)
-  (let lp ((l rev-head) (acc tail))
-    (if (null? l)
-      acc
-      (lp (cdr l) (cons (car l) acc)))))
-
-(define (append-reverse! rev-head tail)
-  (append-reverse rev-head tail))	; XXX:optimize
-
 (define (zip clist1 . rest)
   (let lp ((l (cons clist1 rest)) (acc '()))
     (if (any null? l)