From 58b9c7a6e4bd4296852bdfbc819feab1ae637c49 Mon Sep 17 00:00:00 2001
From: Jay McCarthy <jay@racket-lang.org>
Date: Fri, 13 Aug 2010 15:00:42 -0600
Subject: [PATCH] Fixing seqn-count

---
 collects/racket/private/sequence.rkt           |  8 ++++++--
 collects/scribblings/reference/sequences.scrbl |  4 ++--
 collects/tests/racket/for.rktl                 | 15 +++++++++------
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/collects/racket/private/sequence.rkt b/collects/racket/private/sequence.rkt
index 972f0d2258..fdfdd3677b 100644
--- a/collects/racket/private/sequence.rkt
+++ b/collects/racket/private/sequence.rkt
@@ -222,11 +222,15 @@
         (λ _ #t)
         (λ _ #t)))))
   
-  (define (seqn-count s)
+  (define (seqn-count f s)
+    (unless (procedure? f)
+      (error 'seqn-count "expects a procedure as the first argument, given ~e" f))
     (define-values (more? next) (sequence-generate s))
     (let loop ([n 0])
       (if (more?)
-          (begin (next) (loop (add1 n)))
+          (if (call-with-values next f)
+              (loop (add1 n))
+              (loop n))
           n)))
   
   (provide empty-seqn
diff --git a/collects/scribblings/reference/sequences.scrbl b/collects/scribblings/reference/sequences.scrbl
index b0a9ba6724..b523b40be1 100644
--- a/collects/scribblings/reference/sequences.scrbl
+++ b/collects/scribblings/reference/sequences.scrbl
@@ -149,9 +149,9 @@ then operations on this sequence will not terminate during that infinite sub-seq
          sequence?]{
 Returns a sequence whose elements are the elements of @scheme[s] except in between each is @scheme[e]. The new sequence is constructed lazily. }
                    
-@defproc[(seqn-count [s sequence?])
+@defproc[(seqn-count [f procedure?] [s sequence?])
          exact-nonnegative-integer?]{
-Returns the number of elements in @scheme[s]. If @scheme[s] is infinite, this function does not terminate. }
+Returns the number of elements in @scheme[s] for which @scheme[f] returns a true result. If @scheme[s] is infinite, this function does not terminate. }
                   
 @defproc*[([(in-range [end number?]) sequence?]
            [(in-range [start number?] [end number?] [step number? 1]) sequence?])]{
diff --git a/collects/tests/racket/for.rktl b/collects/tests/racket/for.rktl
index 675b9724ff..de8f332360 100644
--- a/collects/tests/racket/for.rktl
+++ b/collects/tests/racket/for.rktl
@@ -385,11 +385,14 @@
 (test 1 'seqn-add-between (seqn-ref (seqn-add-between (in-naturals) #t) 2))
 (test #t 'seqn-add-between (seqn-ref (seqn-add-between (in-naturals) #t) 3))
 
-(arity-test seqn-count 1 1)
-(test 0 'seqn-count (seqn-count empty-seqn))
-(test 1 'seqn-count (seqn-count (in-range 1)))
-(test 10 'seqn-count (seqn-count (in-range 10)))
-(let ([r (random 100)])
-  (test r 'seqn-count (seqn-count (in-range r))))
+(arity-test seqn-count 2 2)
+(test 0 'seqn-count (seqn-count even? empty-seqn))
+(test 1 'seqn-count (seqn-count even? (in-range 1)))
+(test 5 'seqn-count (seqn-count even? (in-range 10)))
+(let* ([r (random 100)]
+       [a (if (even? r)
+              (/ r 2)
+              (ceiling (/ r 2)))])
+  (test a 'seqn-count (seqn-count even? (in-range r))))
 
 (report-errs)