mtl-unleashed (empty) → 0.2

raw patch · 4 files changed

+142/−0 lines, 4 filesdep +basedep +mtlsetup-changed

Dependencies added: base, mtl

Files

• Control/Monad/Readers.hs +54/−0
• Control/Monad/States.hs +54/−0
• Setup.hs +3/−0
• mtl-unleashed.cabal +31/−0

@@ -0,0 +1,54 @@+-- | MonadState without the function dependency @m -> s@.+{-# LANGUAGE FlexibleInstances #-}+{-# LANGUAGE MultiParamTypeClasses #-}+module Control.Monad.Readers+    ( module Control.Monad.Reader+    , MonadReaders(ask, local)+    , asks+    ) where++import Control.Monad.Reader hiding (MonadReader(ask, local, reader), asks)+import qualified Control.Monad.Reader as MTL (ask, local)+import Control.Monad.State (StateT, get, evalStateT)+import Control.Monad.Writer (runWriterT, WriterT)++-- | Version of MonadReader modified to remove the functional dependency.+class Monad m => MonadReaders r m where+    ask :: m r+    ask = reader id++    local :: (r -> r) -> m a -> m a++    reader :: (r -> a) -> m a+    reader f = do+      r <- ask+      return (f r)++instance Monad m => MonadReaders r (ReaderT r m) where+    ask = MTL.ask+    local = MTL.local++instance (Monad m, MonadReaders r m) => MonadReaders r (StateT s m) where+    ask = lift ask+    local f action = get >>= lift . local f . evalStateT action++instance (Monad m, Monoid w, MonadReaders r m) => MonadReaders r (WriterT w m) where+    ask = lift ask+    local f action = lift (local f (runWriterT action >>= return . fst))++{-+-- Here is how you create a MonadReaders instance for a type that is+-- nested inside another MonadReaders instances.   You need to declare+-- this with the exact parent type (here Bar) or you will get+-- overlapping instances.++instance (Monad m, MonadReaders Foo m) => MonadReaders Foo (ReaderT Bar m) where+    ask = lift ask+    local f action = MTL.ask >>= runReaderT (local f (lift action))+-}++-- | Retrieves a function of the current environment.+asks :: MonadReaders r m+    => (r -> a) -- ^ The selector function to apply to the environment.+    -> m a+asks = reader

@@ -0,0 +1,54 @@+-- | MonadState without the function dependency @m -> s@.+{-# LANGUAGE FlexibleInstances #-}+{-# LANGUAGE MultiParamTypeClasses #-}+module Control.Monad.States+    ( module Control.Monad.State+    , MonadStates(get, put)+    , modify+    , modify'+    , gets+    ) where++import Control.Monad.Reader+import Control.Monad.State hiding (MonadState(get, put, state), modify, modify', gets)+import qualified Control.Monad.State as MTL (get, put)+import Control.Monad.Writer (WriterT)++-- | Copy of 'Control.Monad.State.MonadState' with functional dependency m -> s removed.+class Monad m => MonadStates s m where+    get :: m s+    get = state (\s -> (s, s))+    put :: s -> m ()+    put s = state (\_ -> ((), s))+    state :: (s -> (a, s)) -> m a+    state f = do+      s <- get+      let ~(a, s') = f s+      put s'+      return a++-- | Copy of 'Control.Monad.State.mondify'+modify :: MonadStates s m => (s -> s) -> m ()+modify f = state (\s -> ((), f s))++-- | Copy of 'Control.Monad.State.modify''+modify' :: MonadStates s m => (s -> s) -> m ()+modify' f = state (\s -> let s' = f s in s' `seq` ((), s'))++-- | Copy of 'Control.Monad.State.gets'+gets :: MonadStates s m => (s -> a) -> m a+gets f = do+    s <- get+    return (f s)++instance Monad m => MonadStates s (StateT s m) where+    get = MTL.get+    put = MTL.put++instance (Monad m, MonadStates s m) => MonadStates s (ReaderT r m) where+    get = lift get+    put s = lift $ put s++instance (Monad m, Monoid w, MonadStates s m) => MonadStates s (WriterT w m) where+    get = lift get+    put = lift . put

@@ -0,0 +1,3 @@+import Distribution.Simple+main :: IO ()+main = defaultMain

@@ -0,0 +1,31 @@+name:               mtl-unleashed+version:            0.2+cabal-version:      >= 1.10+build-type:         Simple+license:            BSD3+category:           Control+author:             David Fox+copyright:          (c) 2015 David Fox+maintainer:         David Fox <dsf@seereason.com>+homepage:           https://github.com/seereason/mtl-unleashed+bug-reports:        https://github.com/seereason/mtl-unleashed/issues+stability:          experimental+synopsis:           MTL classes without the functional dependency+description:+  Classes MonadState and MonadReader without the functional+  dependency from the monad to the contained type.  This allows+  more flexibility to extract bits and pieces of state based on+  type, but increases ambiguities that need to be resolved with+  extra type signatures.++library+  build-depends: base < 5, mtl+  ghc-options: -Wall -O2+  exposed-modules:+    Control.Monad.Readers+    Control.Monad.States+  default-language: Haskell2010++source-repository head+  type:     git+  location: git://github.com/seereason/mtl-unleashed.git