mmorph 1.0.6 → 1.0.7

raw patch · 2 files changed

+30/−26 lines, 2 filesdep ~basedep ~mtlPVP: major bump suggested

API removals or changes: PVP suggests a major version bump

Dependency ranges changed: base, mtl

API changes (from Hackage documentation)

Files

• mmorph.cabal +1/−1
• src/Control/Monad/Morph.hs +29/−25

@@ -1,5 +1,5 @@ Name: mmorph-Version: 1.0.6+Version: 1.0.7 Cabal-Version: >= 1.8.0.2 Build-Type: Simple License: BSD3

@@ -1,4 +1,4 @@-{-# LANGUAGE CPP, RankNTypes #-}+{-# LANGUAGE CPP, RankNTypes, PolyKinds #-}  {-| A monad morphism is a natural transformation: @@ -8,13 +8,13 @@  > morph $ do x <- m  =  do x <- morph m >            f x           morph (f x)-> +> > morph (return x) = return x      ... which are equivalent to the following two functor laws:  > morph . (f >=> g) = morph . f >=> morph . g-> +> > morph . return = return      Examples of monad morphisms include:@@ -81,7 +81,7 @@ import qualified Control.Monad.Trans.Reader        as R import qualified Control.Monad.Trans.RWS.Lazy      as RWS import qualified Control.Monad.Trans.RWS.Strict    as RWS'-import qualified Control.Monad.Trans.State.Lazy    as S +import qualified Control.Monad.Trans.State.Lazy    as S import qualified Control.Monad.Trans.State.Strict  as S' import qualified Control.Monad.Trans.Writer.Lazy   as W' import qualified Control.Monad.Trans.Writer.Strict as W@@ -100,14 +100,18 @@ {-| A functor in the category of monads, using 'hoist' as the analog of 'fmap':  > hoist (f . g) = hoist f . hoist g-> +> > hoist id = id -} class MFunctor t where     {-| Lift a monad morphism from @m@ to @n@ into a monad morphism from         @(t m)@ to @(t n)@     -}-    hoist :: (Monad m) => (forall a . m a -> n a) -> t m b -> t n b+#if MIN_VERSION_base(4,8,0)+    hoist :: Functor m => (forall a . m a -> n a) -> t m b -> t n b+#else+    hoist :: Monad m => (forall a . m a -> n a) -> t m b -> t n b+#endif  instance MFunctor (E.ErrorT e) where     hoist nat m = E.ErrorT (nat (E.runErrorT m))@@ -167,9 +171,9 @@     analog of 'return' and 'embed' as the analog of ('=<<'):  > embed lift = id-> +> > embed f (lift m) = f m-> +> > embed g (embed f t) = embed (\m -> embed g (f m)) t -} class (MFunctor t, MonadTrans t) => MMonad t where@@ -231,7 +235,7 @@ {-# INLINABLE (|>=) #-}  instance (E.Error e) => MMonad (E.ErrorT e) where-    embed f m = E.ErrorT (do +    embed f m = E.ErrorT (do         x <- E.runErrorT (f (E.runErrorT m))         return (case x of             Left         e  -> Left e@@ -239,7 +243,7 @@             Right (Right a) -> Right a ) )  instance MMonad (Ex.ExceptT e) where-    embed f m = Ex.ExceptT (do +    embed f m = Ex.ExceptT (do         x <- Ex.runExceptT (f (Ex.runExceptT m))         return (case x of             Left         e  -> Left e@@ -286,7 +290,7 @@     Imagine that some library provided the following 'S.State' code:  > import Control.Monad.Trans.State-> +> > tick :: State Int () > tick = modify (+1) @@ -313,23 +317,23 @@     to be any monad:  > import Data.Functor.Identity-> +> > generalize :: (Monad m) => Identity a -> m a > generalize m = return (runIdentity m)      ... which we can 'hoist' to change @tick@'s base monad:  > hoist :: (Monad m, MFunctor t) => (forall a . m a -> n a) -> t m b -> t n b-> +> > hoist generalize :: (Monad m, MFunctor t) => t Identity b -> t m b-> +> > hoist generalize tick :: (Monad m) => StateT Int m ()      This lets us mix @tick@ alongside 'IO' using 'lift':  > import Control.Monad.Morph > import Control.Monad.Trans.Class-> +> > tock                        ::                   StateT Int IO () > tock = do >     hoist generalize tick   :: (Monad      m) => StateT Int m  ()@@ -348,29 +352,29 @@     morphism laws:  > generalize (return x)-> +> > -- Definition of 'return' for the Identity monad > = generalize (Identity x)-> +> > -- Definition of 'generalize' > = return (runIdentity (Identity x))-> +> > -- runIdentity (Identity x) = x > = return x  > generalize $ do x <- m >                 f x-> +> > -- Definition of (>>=) for the Identity monad > = generalize (f (runIdentity m))-> +> > -- Definition of 'generalize' > = return (runIdentity (f (runIdentity m)))-> +> > -- Monad law: Left identity > = do x <- return (runIdentity m) >      return (runIdentity (f x))-> +> > -- Definition of 'generalize' in reverse > = do x <- generalize m >      generalize (f x)@@ -384,7 +388,7 @@     For example, we might want to combine the following @save@ function:  > import Control.Monad.Trans.Writer-> +> > -- i.e. :: StateT Int (WriterT [Int] Identity) () > save    :: StateT Int (Writer  [Int]) () > save = do@@ -405,7 +409,7 @@     generalizing @save@'s base monad:  > import Control.Monad-> +> > program ::                   StateT Int (WriterT [Int] IO) () > program = replicateM_ 4 $ do >     hoist lift tock@@ -429,7 +433,7 @@ > import Control.Exception > import Control.Monad.Trans.Class > import Control.Monad.Trans.Error-> +> > check :: IO a -> ErrorT IOException IO a > check io = ErrorT (try io)