[commit: packages/bytestring] master: Fix unfoldrN to call the predicate at most n times. (8c3c7f3)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/bytestring

On branch  : master
Link       : http://git.haskell.org/packages/bytestring.git/commitdiff/8c3c7f34ddc03089b1150c7c188fcaf72ef483de

>---------------------------------------------------------------

commit 8c3c7f34ddc03089b1150c7c188fcaf72ef483de
Author: Duncan Coutts <duncan at community.haskell.org>
Date:   Sun Dec 14 16:19:24 2014 +0000

    Fix unfoldrN to call the predicate at most n times.
    
    As a consequence unfoldrN 0 (const Nothing) 0 is now ("", Just 0) where
    before it was ("", Nothing). The other tests still pass.
    
    This fixes issue #11.


>---------------------------------------------------------------

8c3c7f34ddc03089b1150c7c188fcaf72ef483de
 Data/ByteString.hs | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/Data/ByteString.hs b/Data/ByteString.hs
index 5240930..acd0a0f 100644
--- a/Data/ByteString.hs
+++ b/Data/ByteString.hs
@@ -825,13 +825,13 @@ unfoldrN :: Int -> (a -> Maybe (Word8, a)) -> a -> (ByteString, Maybe a)
 unfoldrN i f x0
     | i < 0     = (empty, Just x0)
     | otherwise = unsafePerformIO $ createAndTrim' i $ \p -> go p x0 0
-  where go !p !x !n =
-          case f x of
-            Nothing      -> return (0, n, Nothing)
-            Just (w,x')
-             | n == i    -> return (0, n, Just x)
-             | otherwise -> do poke p w
-                               go (p `plusPtr` 1) x' (n+1)
+  where
+    go !p !x !n
+      | n == i    = return (0, n, Just x)
+      | otherwise = case f x of
+                      Nothing     -> return (0, n, Nothing)
+                      Just (w,x') -> do poke p w
+                                        go (p `plusPtr` 1) x' (n+1)
 {-# INLINE unfoldrN #-}
 
 -- ---------------------------------------------------------------------