Repository : ssh://darcs.haskell.org//srv/darcs/packages/base On branch : monad-comp
http://hackage.haskell.org/trac/ghc/changeset/41839f14458d79ac02ad11087885c7f4f1144a73 >--------------------------------------------------------------- commit 41839f14458d79ac02ad11087885c7f4f1144a73 Author: Nils Schweinsberg <[email protected]> Date: Fri Apr 29 18:16:56 2011 +0200 monad comprehensions: Group and Zip monad ticket #4370 >--------------------------------------------------------------- Control/Monad/Group.hs | 33 +++++++++++++++++++++++++++++++++ Control/Monad/Zip.hs | 46 ++++++++++++++++++++++++++++++++++++++++++++++ base.cabal | 2 ++ 3 files changed, 81 insertions(+), 0 deletions(-) diff --git a/Control/Monad/Group.hs b/Control/Monad/Group.hs new file mode 100644 index 0000000..baab7da --- /dev/null +++ b/Control/Monad/Group.hs @@ -0,0 +1,33 @@ +----------------------------------------------------------------------------- +-- | +-- Module : Control.Monad.Group +-- Copyright : (c) Nils Schweinsberg 2011, +-- (c) University Tuebingen 2011 +-- License : BSD-style (see the file libraries/base/LICENSE) +-- Maintainer : [email protected] +-- Stability : experimental +-- Portability : non-portable +-- +-- Monadic grouping (used for monad comprehensions) +-- +----------------------------------------------------------------------------- + +{-# LANGUAGE CPP, MultiParamTypeClasses, FlexibleInstances #-} + +module Control.Monad.Group where + +import Prelude +#if defined(__GLASGOW_HASKELL__) +import GHC.Exts (groupWith) +#endif + +-- | `MonadGroup` type class without restrictions on the type `t` +class Monad m => MonadGroup m t where + mgroupWith :: (a -> t) -> m a -> m (m a) + +#if defined(__GLASGOW_HASKELL__) +-- | Grouping instance for lists using the `groupWith` function from the +-- "GHC.Exts" library +instance Ord t => MonadGroup [] t where + mgroupWith = groupWith +#endif diff --git a/Control/Monad/Zip.hs b/Control/Monad/Zip.hs new file mode 100644 index 0000000..d6475b8 --- /dev/null +++ b/Control/Monad/Zip.hs @@ -0,0 +1,46 @@ +----------------------------------------------------------------------------- +-- | +-- Module : Control.Monad.Zip +-- Copyright : (c) Nils Schweinsberg 2011, +-- (c) University Tuebingen 2011 +-- License : BSD-style (see the file libraries/base/LICENSE) +-- Maintainer : [email protected] +-- Stability : experimental +-- Portability : portable +-- +-- Monadic zipping (used for monad comprehensions) +-- +----------------------------------------------------------------------------- + +module Control.Monad.Zip where + +import Prelude +import Control.Monad (liftM) + +-- | `MonadZip` type class. Minimal definition: `mzip` or `mzipWith` +-- +-- Instances should satisfy the laws: +-- +-- * Naturality : +-- +-- > liftM (f *** g) (mzip ma mb) = mzip (liftM f ma) (liftM g mb) +-- +-- * Information Preservation: +-- +-- > liftM (const ()) ma = liftM (const ()) mb +-- > ==> +-- > munzip (mzip ma mb) = (ma, mb) +-- +class Monad m => MonadZip m where + + mzip :: m a -> m b -> m (a,b) + mzip = mzipWith (,) + + 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 :: MonadZip m => m (a,b) -> (m a, m b) +munzip mab = (liftM fst mab, liftM snd mab) diff --git a/base.cabal b/base.cabal index b4a6ee7..5478cc3 100644 --- a/base.cabal +++ b/base.cabal @@ -121,6 +121,8 @@ Library { Control.Monad.ST Control.Monad.ST.Lazy Control.Monad.ST.Strict + Control.Monad.Group + Control.Monad.Zip Data.Bits, Data.Bool, Data.Char, _______________________________________________ Cvs-libraries mailing list [email protected] http://www.haskell.org/mailman/listinfo/cvs-libraries
