add gpick

3 files changed, 22 insertions, 1 deletions

diff --git a/mew.scm b/mew.scm
index 05af49b..a56d4ec 100644
--- a/mew.scm
+++ b/mew.scm
@@ -7,7 +7,7 @@
      empty? eof esc
      fin final for fun*
      gconcatenate gen generic-for-each genumerate get gfix giterate gmatch
-     group-by-accumulator gslice-when gsplit gwindow
+     gpick group-by-accumulator gslice-when gsplit gwindow
      inc inject into
      juxt
      keys
@@ -403,6 +403,16 @@
                   (loop))
                 v)))))))
 
+  (define (gpick f gen)
+    (lambda ()
+      (let loop ((item (gen)))
+        (if (eof-object? item)
+          item
+          (let ((v (f item)))
+            (if (eof-object? v)
+              (loop (gen))
+              v))))))
+
   (define (gwindow gen n)
     (let ((window #f))
       (lambda ()
diff --git a/mew.svnwiki b/mew.svnwiki
index 18ae072..6a8432f 100644
--- a/mew.svnwiki
+++ b/mew.svnwiki
@@ -343,6 +343,12 @@ Generator returning {{<val>}}, {{(<fun> <val>)}}, {{(<fun> (<fun (<val>)))}}...
 
 Generator yielding all values of the all generators yielded by {{<gen>}}.
 
+<procedure>(gpick <function> <gen>)<procedure>
+
+Like {{gmap}}, apply {{<function>}} to all values yielded by
+the generator {{<gen>}}, but skip values when {{<function>}} returns
+an eof object.
+
 <procedure>(gwindow <gen> <len>)</procedure>
 
 Generator yielding a sliding window of length {{<len>}} (as a list)
diff --git a/tests/test.mew b/tests/test.mew
index c8c9d16..903620c 100644
--- a/tests/test.mew
+++ b/tests/test.mew
@@ -328,6 +328,11 @@
 
 ; gconcatenate
 
+(test-group "gpick"
+  (test '(2 4 6) (into '() (gpick (fun (x) (if (even? x) x (eof)))
+                                  (generator 1 2 3 4 5 6))))
+  (test '(0 "" #f ()) (into '() (gpick (op) (generator 0 "" #f '())))))
+
 ; gwindow
 
 ; gslice-when