From 848458d99068f7542b5f63d52eb2338595a5fb1e Mon Sep 17 00:00:00 2001
From: Gary Houston <ghouston@arglist.com>
Date: Sat, 4 Aug 2001 18:37:08 +0000
Subject: [PATCH] 	* srfi-1.scm (filter): replaced with a tail-recursive
 version. 	(remove): implement using filter, to make it tail-recursive.

---
 srfi/ChangeLog  |  5 +++++
 srfi/srfi-1.scm | 20 ++++++++++----------
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/srfi/ChangeLog b/srfi/ChangeLog
index 109ff9940..d4b650181 100644
--- a/srfi/ChangeLog
+++ b/srfi/ChangeLog
@@ -1,3 +1,8 @@
+2001-08-04  Gary Houston  <ghouston@arglist.com>
+
+	* srfi-1.scm (filter): replaced with a tail-recursive version.
+	(remove): implement using filter, to make it tail-recursive.
+
 2001-07-31  Gary Houston  <ghouston@arglist.com>
 
 	* srfi-14.c (scm_char_set_diff_plus_intersection): wasn't correctly
diff --git a/srfi/srfi-1.scm b/srfi/srfi-1.scm
index 4c361a57e..cd2ca757d 100644
--- a/srfi/srfi-1.scm
+++ b/srfi/srfi-1.scm
@@ -720,11 +720,15 @@
 ;;; Filtering & partitioning
 
 (define (filter pred list)
-  (if (null? list)
-    '()
-    (if (pred (car list))
-      (cons (car list) (filter pred (cdr list)))
-      (filter pred (cdr list)))))
+  (letrec ((filiter (lambda (pred rest result)
+		      (if (null? rest)
+			  (reverse! result)
+			  (filiter pred (cdr rest)
+				   (cond ((pred (car rest))
+					  (cons (car rest) result))
+					 (else
+					  result)))))))
+    (filiter pred list '())))
 
 (define (partition pred list)
   (if (null? list)
@@ -736,11 +740,7 @@
 	       (values in (cons (car list) out))))))
 
 (define (remove pred list)
-  (if (null? list)
-    '()
-    (if (pred (car list))
-      (remove pred (cdr list))
-      (cons (car list) (remove pred (cdr list))))))
+  (filter (lambda (x) (not (pred x))) list))
 
 (define (filter! pred list)
   (filter pred list))			; XXX:optimize