diff options
| -rw-r--r-- | libraries/base/Control/Monad/Zip.hs | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/libraries/base/Control/Monad/Zip.hs b/libraries/base/Control/Monad/Zip.hs index 8c431bdbfb..9d71a53878 100644 --- a/libraries/base/Control/Monad/Zip.hs +++ b/libraries/base/Control/Monad/Zip.hs @@ -3,6 +3,7 @@ -- | -- Module : Control.Monad.Zip -- Copyright : (c) Nils Schweinsberg 2011, +-- (c) George Giorgidze 2011 -- (c) University Tuebingen 2011 -- License : BSD-style (see the file libraries/base/LICENSE) -- Maintainer : libraries@haskell.org @@ -40,8 +41,13 @@ class Monad m => MonadZip m where mzipWith :: (a -> b -> c) -> m a -> m b -> m c mzipWith f ma mb = liftM (uncurry f) (mzip ma mb) -instance MonadZip [] where - mzip = zip + munzip :: m (a,b) -> (m a, m b) + munzip mab = (liftM fst mab, liftM snd mab) + -- munzip is a member of the class because sometimes + -- you can implement it more efficiently than the + -- above default code. See Trac #4370 comment by giorgidze -munzip :: MonadZip m => m (a,b) -> (m a, m b) -munzip mab = (liftM fst mab, liftM snd mab) +instance MonadZip [] where + mzip = zip + mzipWith = zipWith + munzip = unzip
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