filter-map tail recursion

[Kevin Ryde]

        * srfi-1.scm (filter-map): Use tail recursion, to avoid stack overflow.

I'm thinking of this for 1.6 too, if 1.8 is still a while away.  And
various other tail recursions I've put just in 1.8 too.  Hitting
overflows on just a few thousand elements is no fun.

--- srfi-1.scm.~1.33.~  2004-08-27 10:14:23.000000000 +1000
+++ srfi-1.scm  2004-09-28 17:59:16.000000000 +1000
@@ -567,20 +567,22 @@
 
 (define (filter-map f clist1 . rest)
   (if (null? rest)
-    (let lp ((l clist1))
+    (let lp ((l clist1)
+            (rl '()))
       (if (null? l)
-       '()
+       (reverse! rl)
        (let ((res (f (car l))))
          (if res
-           (cons res (lp (cdr l)))
-           (lp (cdr l))))))
-    (let lp ((l (cons clist1 rest)))
+           (lp (cdr l) (cons res rl))
+           (lp (cdr l) rl)))))
+    (let lp ((l (cons clist1 rest))
+            (rl '()))
       (if (any1 null? l)
-       '()
+       (reverse! rl)
        (let ((res (apply f (map1 car l))))
          (if res
-           (cons res (lp (map1 cdr l)))
-           (lp (map1 cdr l))))))))
+           (lp (map1 cdr l) (cons res rl))
+           (lp (map1 cdr l) rl)))))))
 
 ;;; Filtering & partitioning
 

--- srfi-1.test.~1.9.~  2003-12-03 08:18:16.000000000 +1100
+++ srfi-1.test 2004-11-30 17:54:42.000000000 +1100
@@ -458,6 +458,50 @@
            (drop '(a b . c) 2))))
 
 ;;
+;; filter-map
+;;
+
+(with-test-prefix "filter-map"
+
+  (with-test-prefix "one list"
+    (pass-if "(1)"
+      (equal? '(1) (filter-map noop '(1))))
+
+    (pass-if "(#f)"
+      (equal? '() (filter-map noop '(#f))))
+
+    (pass-if "(1 2)"
+      (equal? '(1 2) (filter-map noop '(1 2))))
+
+    (pass-if "(#f 2)"
+      (equal? '(2) (filter-map noop '(#f 2))))
+
+    (pass-if "(#f #f)"
+      (equal? '() (filter-map noop '(#f #f))))
+
+    (pass-if "(1 2 3)"
+      (equal? '(1 2 3) (filter-map noop '(1 2 3))))
+
+    (pass-if "(#f 2 3)"
+      (equal? '(2 3) (filter-map noop '(#f 2 3))))
+
+    (pass-if "(1 #f 3)"
+      (equal? '(1 3) (filter-map noop '(1 #f 3))))
+
+    (pass-if "(1 2 #f)"
+      (equal? '(1 2) (filter-map noop '(1 2 #f)))))
+
+  (with-test-prefix "two lists"
+    (pass-if "(1 2 3) (4 5 6)"
+      (equal? '(1 2 3) (filter-map noop '(1 2 3) '(4 5 6))))
+
+    (pass-if "(#f 2 3) (4 5)"
+      (equal? '(2) (filter-map noop '(#f 2 3) '(4 5))))
+
+    (pass-if "(4 #f) (1 2 3)"
+      (equal? '(4) (filter-map noop '(4 #f) '(1 2 3))))))
+  
+;;
 ;; length+
 ;;