monad-control-1.0.0.4/0000755000000000000000000000000012467453274012632 5ustar0000000000000000monad-control-1.0.0.4/CHANGELOG0000644000000000000000000003155512467453274014055 0ustar00000000000000001.0.0.4 * Support transformers-compat-0.4.*. 1.0.0.3 * Unconditionally add ExceptT instances using transformers-compat. Courtesy of Adam Bergmark. 1.0.0.2 * Add a base >= 4.5 constraint because monad-control only builds on GHC >= 7.4. 1.0.0.1 * Use Safe instead of Trustworthy. This requires a dependency on stm. 1.0.0.0 * Switch the associated data types StT and StM to associated type synonyms. This is an API breaking change. To fix your MonadTransControl or MonadBaseControl instances simply remove the StT or StM constructors and deconstructors for your monad transformers or monad. * Add the embed, embed_ and liftBaseOpDiscard functions. 0.3.3.0 * Support transformers-0.4.0.0 * Drop unicode syntax and symbols 0.3.2.3 * Fix haddock documentation error 0.3.2.2 * Fix preprocessor directive for GHC 7.6.3 0.3.2.1 * Resolve #14. Bump upper version bound of base to 5 0.3.2 * Added defaultLiftWith and defaultRestoreT to simplify defining MonadTransControl for newtypes. 0.3.1.4 * Compatibility with ghc head 0.3.1.3 * Added a Trustworthy flag 0.3.1.2 * Fix issue #9. Replace all Unicode in type variables. 0.3.1.1 * Add MonadBaseControl instances for ST and STM. 0.3 (Released on: Fri Dec 2 09:52:16 UTC 2011) * Major new API which IMHO is easier to understand than the old one. * On average about 60 times faster than the previous release! * New package lifted-base providing lifted versions of functions from the base library. It exports the following modules: - Control.Exception.Lifted - Control.Concurrent.Lifted - Control.Concurrent.MVar.Lifted - System.Timeout.Lifted Not all modules from base are converted yet. If you need a lifted version of some function from base, just ask me to add it or send me a patch. 0.2.0.3 (Released on: Sat Aug 27 21:18:22 UTC 2011) * Fixed issue #2 https://github.com/basvandijk/monad-control/issues/2 0.2.0.2 (Released on: Mon Aug 8 09:16:08 UTC 2011) * Switched to git on github. * Tested with base-4.4 and ghc-7.2.1. * Use the new cabal test-suite feature. 0.2.0.1 (Released on: Wed Mar 16 15:53:50 UTC 2011) * Added laws for MonadTransControl and MonadControlIO * Bug fix: Add proper laziness to the MonadTransControl instances of the lazy StateT, WriteT and RWST These all failed the law: control $ \run -> run t = t where t = return undefined * Add INLINABLE pragmas for most public functions A simple benchmark showed some functions (bracket and mask) improving by 30%. 0.2 (Released on: Wed Feb 9 12:05:26 UTC 2011) * Use RunInBase in the type of idLiftControl. * Added this NEWS file. * Only parameterize Run with t and use RankNTypes to quantify n and o -liftControl :: (Monad m, Monad n, Monad o) => (Run t n o -> m a) -> t m a +liftControl :: Monad m => (Run t -> m a) -> t m a -type Run t n o = forall b. t n b -> n (t o b) +type Run t = forall n o b. (Monad n, Monad o, Monad (t o)) => t n b -> n (t o b) Bumped version from 0.1 to 0.2 to indicate this breaking change in API. * Added example of a derivation of liftControlIO. Really enlightening! 0.1 (Released on: Sat Feb 5 23:36:21 UTC 2011) * Initial release This is the announcement message sent to the Haskell mailinglists: http://www.mail-archive.com/haskell@haskell.org/msg23278.html Dear all, Several attempts have been made to lift control operations (functions that use monadic actions as input instead of just output) through monad transformers: MonadCatchIO-transformers[1] provided a type class that allowed to overload some often used control operations (catch, block and unblock). Unfortunately that library was limited to those operations. It was not possible to use, say, alloca in a monad transformer. More importantly however, the library was broken as was explained[2] by Michael Snoyman. In response Michael created the MonadInvertIO type class which solved the problems. Then Anders Kaseorg created the monad-peel library which provided an even nicer implementation. monad-control is a rewrite of monad-peel that uses CPS style operations and exploits the RankNTypes language extension to simplify and speedup most functions. A very preliminary and not yet fully representative, benchmark shows that monad-control is on average about 2.6 times faster than monad-peel: bracket: 2.4 x faster bracket_: 3.1 x faster catch: 1.8 x faster try: 4.0 x faster mask: 2.0 x faster Note that, although the package comes with a test suite that passes, I still consider it highly experimental. API DOCS: http://hackage.haskell.org/package/monad-control INSTALLING: $ cabal update $ cabal install monad-control TESTING: The package contains a copy of the monad-peel test suite written by Anders. You can perform the tests using: $ cabal unpack monad-control $ cd monad-control $ cabal configure -ftest $ cabal test BENCHMARKING: $ darcs get http://bifunctor.homelinux.net/~bas/bench-monad-peel-control/ $ cd bench-monad-peel-control $ cabal configure $ cabal build $ dist/build/bench-monad-peel-control/bench-monad-peel-control DEVELOPING: The darcs repository will be hosted on code.haskell.org ones that server is back online. For the time being you can get the repository from: $ darcs get http://bifunctor.homelinux.net/~bas/monad-control/ TUTORIAL: This short unpolished tutorial will explain how to lift control operations through monad transformers. Our goal is to lift a control operation like: foo ∷ M a → M a where M is some monad, into a transformed monad like 'StateT M': foo' ∷ StateT M a → StateT M a The first thing we need to do is write an instance for the MonadTransControl type class: class MonadTrans t ⇒ MonadTransControl t where liftControl ∷ (Monad m, Monad n, Monad o) ⇒ (Run t n o → m a) → t m a If you ignore the Run argument for now, you'll see that liftControl is identical to the 'lift' method of the MonadTrans type class: class MonadTrans t where lift ∷ Monad m ⇒ m a → t m a So the instance for MonadTransControl will probably look very much like the instance for MonadTrans. Let's see: instance MonadTransControl (StateT s) where liftControl f = StateT $ \s → liftM (\x → (x, s)) (f run) So what is this run function? Let's look at its type: type Run t n o = ∀ b. t n b → n (t o b) The run function executes a transformed monadic action 't n b' in the non-transformed monad 'n'. In our case the 't' will be a StateT computation. The only way to run a StateT computation is to give it some state and the only state we have lying around is the one from the outer computation: 's'. So let's run it on 's': instance MonadTransControl (StateT s) where liftControl f = StateT $ \s → let run t = ... runStateT t s ... in liftM (\x → (x, s)) (f run) Now that we are able to run a transformed monadic action, we're almost done. Look at the type of Run again. The function should leave the result 't o b' in the monad 'n'. This 't o b' computation should contain the final state after running the supplied 't n b' computation. In case of our StateT it should contain the final state s': instance MonadTransControl (StateT s) where liftControl f = StateT $ \s → let run t = liftM (\(x, s') → StateT $ \_ → return (x, s')) (runStateT t s) in liftM (\x → (x, s)) (f run) This final computation, "StateT $ \_ → return (x, s')", can later be used to restore the final state. Now that we have our MonadTransControl instance we can start using it. Recall that our goal was to lift "foo ∷ M a → M a" into our StateT transformer yielding the function "foo' ∷ StateT M a → StateT M a". To define foo', the first thing we need to do is call liftControl: foo' t = liftControl $ \run → ... This captures the current state of the StateT computation and provides us with the run function that allows us to run a StateT computation on this captured state. Now recall the type of liftControl ∷ (Run t n o → m a) → t m a. You can see that in place of the ... we must fill in a value of type 'm a'. In our case this will be a value of type 'M a'. We can construct such a value by calling foo. However, foo expects an argument of type 'M a'. Fortunately we can provide one if we convert the supplied 't' computation of type 'StateT M a' to 'M a' using our run function of type ∀ b. StateT M b → M (StateT o b): foo' t = ... liftControl $ \run → foo $ run t However, note that the run function returns the final StateT computation inside M. So the type of the right hand side is now 'StateT M (StateT o b)'. We would like to restore this final state. We can do that using join: foo' t = join $ liftControl $ \run → foo $ run t That's it! Note that because it's so common to join after a liftControl I provide an abstraction for it: control = join ∘ liftControl Allowing you to simplify foo' to: foo' t = control $ \run → foo $ run t Probably the most common control operations that you want to lift through your transformers are IO operations. Think about: bracket, alloca, mask, etc.. For this reason I provide the MonadControlIO type class: class MonadIO m ⇒ MonadControlIO m where liftControlIO ∷ (RunInBase m IO → IO a) → m a Again, if you ignore the RunInBase argument, you will see that liftControlIO is identical to the liftIO method of the MonadIO type class: class Monad m ⇒ MonadIO m where liftIO ∷ IO a → m a Just like Run, RunInBase allows you to run your monadic computation inside your base monad, which in case of liftControlIO is IO: type RunInBase m base = ∀ b. m b → base (m b) The instance for the base monad is trivial: instance MonadControlIO IO where liftControlIO = idLiftControl idLiftControl directly executes f and passes it a run function which executes the given action and lifts the result r into the trivial 'return r' action: idLiftControl ∷ Monad m ⇒ ((∀ b. m b → m (m b)) → m a) → m a idLiftControl f = f $ liftM $ \r -> return r The instances for the transformers are all identical. Let's look at StateT and ReaderT: instance MonadControlIO m ⇒ MonadControlIO (StateT s m) where liftControlIO = liftLiftControlBase liftControlIO instance MonadControlIO m ⇒ MonadControlIO (ReaderT r m) where liftControlIO = liftLiftControlBase liftControlIO The magic function is liftLiftControlBase. This function is used to compose two liftControl operations, the outer provided by a MonadTransControl instance and the inner provided as the argument: liftLiftControlBase ∷ (MonadTransControl t, Monad base, Monad m, Monad (t m)) ⇒ ((RunInBase m base → base a) → m a) → ((RunInBase (t m) base → base a) → t m a) liftLiftControlBase lftCtrlBase = \f → liftControl $ \run → lftCtrlBase $ \runInBase → f $ liftM (join ∘ lift) ∘ runInBase ∘ run Basically it captures the state of the outer monad transformer using liftControl. Then it captures the state of the inner monad using the supplied lftCtrlBase function. If you recall the identical definitions of the liftControlIO methods: 'liftLiftControlBase liftControlIO' you will see that this lftCtrlBase function is the recursive step of liftLiftControlBase. If you use 'liftLiftControlBase liftControlIO' in a stack of monad transformers a chain of liftControl operations is created: liftControl $ \run1 -> liftControl $ \run2 -> liftControl $ \run3 -> ... This will recurse until we hit the base monad. Then liftLiftControlBase will finally run f in the base monad supplying it with a run function that is able to run a 't m a' computation in the base monad. It does this by composing the run and runInBase functions. Note that runInBase is basically the composition: '... ∘ run3 ∘ run2'. However, just composing the run and runInBase functions is not enough. Namely: runInBase ∘ run ∷ ∀ b. t m b → base (m (t m b)) while we need to have ∀ b. t m b → base (t m b). So we need to lift the 'm (t m b)' computation inside t yielding: 't m (t m b)' and then join that to get 't m b'. Now that we have our MonadControlIO instances we can start using them. Let's look at how to lift 'bracket' into a monad supporting MonadControlIO. Before we do that I define a little convenience function similar to 'control': controlIO = join ∘ liftControlIO Bracket just calls controlIO which captures the state of m and provides us with a runInIO function which allows us to run an m computation in IO: bracket ∷ MonadControlIO m ⇒ m a → (a → m b) → (a → m c) → m c bracket before after thing = controlIO $ \runInIO → E.bracket (runInIO before) (\m → runInIO $ m >>= after) (\m → runInIO $ m >>= thing) I welcome any comments, questions or patches. Regards, Bas [1] http://hackage.haskell.org/package/MonadCatchIO-transformers [2] http://docs.yesodweb.com/blog/invertible-monads-exceptions-allocations/ [3] http://hackage.haskell.org/package/monad-peel monad-control-1.0.0.4/LICENSE0000644000000000000000000000274412467453274013646 0ustar0000000000000000Copyright © 2010, Bas van Dijk, Anders Kaseorg All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. • Neither the name of the author nor the names of other contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. monad-control-1.0.0.4/Setup.hs0000644000000000000000000000005612467453274014267 0ustar0000000000000000import Distribution.Simple main = defaultMain monad-control-1.0.0.4/README.markdown0000644000000000000000000000152612467453274015337 0ustar0000000000000000This package defines the type class `MonadControlIO`, a subset of `MonadIO` into which generic control operations such as `catch` can be lifted from `IO`. Instances are based on monad transformers in `MonadTransControl`, which includes all standard monad transformers in the `transformers` library except `ContT`. Note that this package is a rewrite of Anders Kaseorg's `monad-peel` library. The main difference is that this package provides CPS style operators and exploits the `RankNTypes` language extension to simplify most definitions. The package includes a copy of the `monad-peel` testsuite written by Anders Kaseorg The tests can be performed by using `cabal test`. [This `criterion`](https://github.com/basvandijk/bench-monad-peel-control) based benchmark shows that `monad-control` is on average about 2.5 times faster than `monad-peel`. monad-control-1.0.0.4/monad-control.cabal0000644000000000000000000000411312467453274016371 0ustar0000000000000000Name: monad-control Version: 1.0.0.4 Synopsis: Lift control operations, like exception catching, through monad transformers License: BSD3 License-file: LICENSE Author: Bas van Dijk, Anders Kaseorg Maintainer: Bas van Dijk Copyright: (c) 2011 Bas van Dijk, Anders Kaseorg Homepage: https://github.com/basvandijk/monad-control Bug-reports: https://github.com/basvandijk/monad-control/issues Category: Control Build-type: Simple Cabal-version: >= 1.6 Description: This package defines the type class @MonadBaseControl@, a subset of @MonadBase@ into which generic control operations such as @catch@ can be lifted from @IO@ or any other base monad. Instances are based on monad transformers in @MonadTransControl@, which includes all standard monad transformers in the @transformers@ library except @ContT@. . See the @lifted-base@ package which uses @monad-control@ to lift @IO@ operations from the @base@ library (like @catch@ or @bracket@) into any monad that is an instance of @MonadBase@ or @MonadBaseControl@. . Note that this package is a rewrite of Anders Kaseorg's @monad-peel@ library. The main difference is that this package provides CPS style operators and exploits the @RankNTypes@ and @TypeFamilies@ language extensions to simplify and speedup most definitions. extra-source-files: README.markdown, CHANGELOG -------------------------------------------------------------------------------- source-repository head type: git location: git://github.com/basvandijk/monad-control.git -------------------------------------------------------------------------------- Library Exposed-modules: Control.Monad.Trans.Control Build-depends: base >= 4.5 && < 5 , stm >= 2.3 && < 3 , transformers >= 0.2 && < 0.5 , transformers-compat >= 0.3 && < 0.5 , transformers-base >= 0.4.4 && < 0.5 Ghc-options: -Wall monad-control-1.0.0.4/Control/0000755000000000000000000000000012467453274014252 5ustar0000000000000000monad-control-1.0.0.4/Control/Monad/0000755000000000000000000000000012467453274015310 5ustar0000000000000000monad-control-1.0.0.4/Control/Monad/Trans/0000755000000000000000000000000012467453274016377 5ustar0000000000000000monad-control-1.0.0.4/Control/Monad/Trans/Control.hs0000644000000000000000000004450512467453274020363 0ustar0000000000000000{-# LANGUAGE CPP , NoImplicitPrelude , RankNTypes , TypeFamilies , FunctionalDependencies , FlexibleInstances , UndecidableInstances , MultiParamTypeClasses #-} #if __GLASGOW_HASKELL__ >= 702 {-# LANGUAGE Safe #-} #endif #if MIN_VERSION_transformers(0,4,0) -- Hide warnings for the deprecated ErrorT transformer: {-# OPTIONS_GHC -fno-warn-warnings-deprecations #-} #endif {- | Module : Control.Monad.Trans.Control Copyright : Bas van Dijk, Anders Kaseorg License : BSD-style Maintainer : Bas van Dijk Stability : experimental -} module Control.Monad.Trans.Control ( -- * MonadTransControl MonadTransControl(..), Run -- ** Defaults for MonadTransControl -- $MonadTransControlDefaults , RunDefault, defaultLiftWith, defaultRestoreT -- * MonadBaseControl , MonadBaseControl (..), RunInBase -- ** Defaults for MonadBaseControl -- $MonadBaseControlDefaults , ComposeSt, RunInBaseDefault, defaultLiftBaseWith, defaultRestoreM -- * Utility functions , control, embed, embed_ , liftBaseOp, liftBaseOp_ , liftBaseDiscard, liftBaseOpDiscard ) where -------------------------------------------------------------------------------- -- Imports -------------------------------------------------------------------------------- -- from base: import Data.Function ( (.), ($), const ) import Data.Monoid ( Monoid, mempty ) import Control.Monad ( Monad, (>>=), return, liftM ) import System.IO ( IO ) import Data.Maybe ( Maybe ) import Data.Either ( Either ) #if MIN_VERSION_base(4,4,0) import Control.Monad.ST.Lazy.Safe ( ST ) import qualified Control.Monad.ST.Safe as Strict ( ST ) #endif -- from stm: import Control.Monad.STM ( STM ) -- from transformers: import Control.Monad.Trans.Class ( MonadTrans ) import Control.Monad.Trans.Identity ( IdentityT(IdentityT), runIdentityT ) import Control.Monad.Trans.List ( ListT (ListT), runListT ) import Control.Monad.Trans.Maybe ( MaybeT (MaybeT), runMaybeT ) import Control.Monad.Trans.Error ( ErrorT (ErrorT), runErrorT, Error ) import Control.Monad.Trans.Reader ( ReaderT (ReaderT), runReaderT ) import Control.Monad.Trans.State ( StateT (StateT), runStateT ) import Control.Monad.Trans.Writer ( WriterT (WriterT), runWriterT ) import Control.Monad.Trans.RWS ( RWST (RWST), runRWST ) import Control.Monad.Trans.Except ( ExceptT (ExceptT), runExceptT ) import qualified Control.Monad.Trans.RWS.Strict as Strict ( RWST (RWST), runRWST ) import qualified Control.Monad.Trans.State.Strict as Strict ( StateT (StateT), runStateT ) import qualified Control.Monad.Trans.Writer.Strict as Strict ( WriterT(WriterT), runWriterT ) import Data.Functor.Identity ( Identity ) -- from transformers-base: import Control.Monad.Base ( MonadBase ) #if MIN_VERSION_base(4,3,0) import Control.Monad ( void ) #else import Data.Functor (Functor, fmap) void :: Functor f => f a -> f () void = fmap (const ()) #endif import Prelude (id) -------------------------------------------------------------------------------- -- MonadTransControl type class -------------------------------------------------------------------------------- class MonadTrans t => MonadTransControl t where -- | Monadic state of @t@. type StT t a :: * -- | @liftWith@ is similar to 'lift' in that it lifts a computation from -- the argument monad to the constructed monad. -- -- Instances should satisfy similar laws as the 'MonadTrans' laws: -- -- @liftWith . const . return = return@ -- -- @liftWith (const (m >>= f)) = liftWith (const m) >>= liftWith . const . f@ -- -- The difference with 'lift' is that before lifting the @m@ computation -- @liftWith@ captures the state of @t@. It then provides the @m@ -- computation with a 'Run' function that allows running @t n@ computations in -- @n@ (for all @n@) on the captured state. liftWith :: Monad m => (Run t -> m a) -> t m a -- | Construct a @t@ computation from the monadic state of @t@ that is -- returned from a 'Run' function. -- -- Instances should satisfy: -- -- @liftWith (\\run -> run t) >>= restoreT . return = t@ restoreT :: Monad m => m (StT t a) -> t m a -- | A function that runs a transformed monad @t n@ on the monadic state that -- was captured by 'liftWith' -- -- A @Run t@ function yields a computation in @n@ that returns the monadic state -- of @t@. This state can later be used to restore a @t@ computation using -- 'restoreT'. type Run t = forall n b. Monad n => t n b -> n (StT t b) -------------------------------------------------------------------------------- -- Defaults for MonadTransControl -------------------------------------------------------------------------------- -- $MonadTransControlDefaults -- -- The following functions can be used to define a 'MonadTransControl' instance -- for a monad transformer which simply wraps another monad transformer which -- already has a @MonadTransControl@ instance. For example: -- -- @ -- {-\# LANGUAGE GeneralizedNewtypeDeriving \#-} -- -- newtype CounterT m a = CounterT {unCounterT :: StateT Int m a} -- deriving (Monad, MonadTrans) -- -- instance MonadTransControl CounterT where -- type StT CounterT a = StT (StateT Int) a -- liftWith = 'defaultLiftWith' CounterT unCounterT -- restoreT = 'defaultRestoreT' CounterT -- @ -- | A function like 'Run' that runs a monad transformer @t@ which wraps the -- monad transformer @t'@. This is used in 'defaultLiftWith'. type RunDefault t t' = forall n b. Monad n => t n b -> n (StT t' b) -- | Default definition for the 'liftWith' method. defaultLiftWith :: (Monad m, MonadTransControl n) => (forall b. n m b -> t m b) -- ^ Monad constructor -> (forall o b. t o b -> n o b) -- ^ Monad deconstructor -> (RunDefault t n -> m a) -> t m a defaultLiftWith t unT = \f -> t $ liftWith $ \run -> f $ run . unT {-# INLINABLE defaultLiftWith #-} -- | Default definition for the 'restoreT' method. defaultRestoreT :: (Monad m, MonadTransControl n) => (n m a -> t m a) -- ^ Monad constructor -> m (StT n a) -> t m a defaultRestoreT t = t . restoreT {-# INLINABLE defaultRestoreT #-} -------------------------------------------------------------------------------- -- MonadTransControl instances -------------------------------------------------------------------------------- instance MonadTransControl IdentityT where type StT IdentityT a = a liftWith f = IdentityT $ f $ runIdentityT restoreT = IdentityT {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance MonadTransControl MaybeT where type StT MaybeT a = Maybe a liftWith f = MaybeT $ liftM return $ f $ runMaybeT restoreT = MaybeT {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance Error e => MonadTransControl (ErrorT e) where type StT (ErrorT e) a = Either e a liftWith f = ErrorT $ liftM return $ f $ runErrorT restoreT = ErrorT {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance MonadTransControl (ExceptT e) where type StT (ExceptT e) a = Either e a liftWith f = ExceptT $ liftM return $ f $ runExceptT restoreT = ExceptT {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance MonadTransControl ListT where type StT ListT a = [a] liftWith f = ListT $ liftM return $ f $ runListT restoreT = ListT {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance MonadTransControl (ReaderT r) where type StT (ReaderT r) a = a liftWith f = ReaderT $ \r -> f $ \t -> runReaderT t r restoreT = ReaderT . const {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance MonadTransControl (StateT s) where type StT (StateT s) a = (a, s) liftWith f = StateT $ \s -> liftM (\x -> (x, s)) (f $ \t -> runStateT t s) restoreT = StateT . const {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance MonadTransControl (Strict.StateT s) where type StT (Strict.StateT s) a = (a, s) liftWith f = Strict.StateT $ \s -> liftM (\x -> (x, s)) (f $ \t -> Strict.runStateT t s) restoreT = Strict.StateT . const {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance Monoid w => MonadTransControl (WriterT w) where type StT (WriterT w) a = (a, w) liftWith f = WriterT $ liftM (\x -> (x, mempty)) (f $ runWriterT) restoreT = WriterT {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance Monoid w => MonadTransControl (Strict.WriterT w) where type StT (Strict.WriterT w) a = (a, w) liftWith f = Strict.WriterT $ liftM (\x -> (x, mempty)) (f $ Strict.runWriterT) restoreT = Strict.WriterT {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance Monoid w => MonadTransControl (RWST r w s) where type StT (RWST r w s) a = (a, s, w) liftWith f = RWST $ \r s -> liftM (\x -> (x, s, mempty)) (f $ \t -> runRWST t r s) restoreT mSt = RWST $ \_ _ -> mSt {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} instance Monoid w => MonadTransControl (Strict.RWST r w s) where type StT (Strict.RWST r w s) a = (a, s, w) liftWith f = Strict.RWST $ \r s -> liftM (\x -> (x, s, mempty)) (f $ \t -> Strict.runRWST t r s) restoreT mSt = Strict.RWST $ \_ _ -> mSt {-# INLINABLE liftWith #-} {-# INLINABLE restoreT #-} -------------------------------------------------------------------------------- -- MonadBaseControl type class -------------------------------------------------------------------------------- class MonadBase b m => MonadBaseControl b m | m -> b where -- | Monadic state of @m@. type StM m a :: * -- | @liftBaseWith@ is similar to 'liftIO' and 'liftBase' in that it -- lifts a base computation to the constructed monad. -- -- Instances should satisfy similar laws as the 'MonadIO' and 'MonadBase' laws: -- -- @liftBaseWith . const . return = return@ -- -- @liftBaseWith (const (m >>= f)) = liftBaseWith (const m) >>= liftBaseWith . const . f@ -- -- The difference with 'liftBase' is that before lifting the base computation -- @liftBaseWith@ captures the state of @m@. It then provides the base -- computation with a 'RunInBase' function that allows running @m@ -- computations in the base monad on the captured state. liftBaseWith :: (RunInBase m b -> b a) -> m a -- | Construct a @m@ computation from the monadic state of @m@ that is -- returned from a 'RunInBase' function. -- -- Instances should satisfy: -- -- @liftBaseWith (\\runInBase -> runInBase m) >>= restoreM = m@ restoreM :: StM m a -> m a -- | A function that runs a @m@ computation on the monadic state that was -- captured by 'liftBaseWith' -- -- A @RunInBase m@ function yields a computation in the base monad of @m@ that -- returns the monadic state of @m@. This state can later be used to restore the -- @m@ computation using 'restoreM'. type RunInBase m b = forall a. m a -> b (StM m a) -------------------------------------------------------------------------------- -- MonadBaseControl instances for all monads in the base library -------------------------------------------------------------------------------- #define BASE(M) \ instance MonadBaseControl (M) (M) where { \ type StM (M) a = a; \ liftBaseWith f = f id; \ restoreM = return; \ {-# INLINABLE liftBaseWith #-}; \ {-# INLINABLE restoreM #-}} BASE(IO) BASE(Maybe) BASE(Either e) BASE([]) BASE((->) r) BASE(Identity) BASE(STM) #if MIN_VERSION_base(4,4,0) BASE(Strict.ST s) BASE( ST s) #endif #undef BASE -------------------------------------------------------------------------------- -- Defaults for MonadBaseControl -------------------------------------------------------------------------------- -- $MonadBaseControlDefaults -- -- Note that by using the following default definitions it's easy to make a -- monad transformer @T@ an instance of 'MonadBaseControl': -- -- @ -- instance MonadBaseControl b m => MonadBaseControl b (T m) where -- type StM (T m) a = 'ComposeSt' T m a -- liftBaseWith = 'defaultLiftBaseWith' -- restoreM = 'defaultRestoreM' -- @ -- -- Defining an instance for a base monad @B@ is equally straightforward: -- -- @ -- instance MonadBaseControl B B where -- type StM B a = a -- liftBaseWith f = f 'id' -- restoreM = 'return' -- @ -- | Handy type synonym that composes the monadic states of @t@ and @m@. -- -- It can be used to define the 'StM' for new 'MonadBaseControl' instances. type ComposeSt t m a = StM m (StT t a) -- | A function like 'RunInBase' that runs a monad transformer @t@ in its base -- monad @b@. It is used in 'defaultLiftBaseWith'. type RunInBaseDefault t m b = forall a. t m a -> b (ComposeSt t m a) -- | Default defintion for the 'liftBaseWith' method. -- -- Note that it composes a 'liftWith' of @t@ with a 'liftBaseWith' of @m@ to -- give a 'liftBaseWith' of @t m@: -- -- @ -- defaultLiftBaseWith = \\f -> 'liftWith' $ \\run -> -- 'liftBaseWith' $ \\runInBase -> -- f $ runInBase . run -- @ defaultLiftBaseWith :: (MonadTransControl t, MonadBaseControl b m) => (RunInBaseDefault t m b -> b a) -> t m a defaultLiftBaseWith = \f -> liftWith $ \run -> liftBaseWith $ \runInBase -> f $ runInBase . run {-# INLINABLE defaultLiftBaseWith #-} -- | Default definition for the 'restoreM' method. -- -- Note that: @defaultRestoreM = 'restoreT' . 'restoreM'@ defaultRestoreM :: (MonadTransControl t, MonadBaseControl b m) => ComposeSt t m a -> t m a defaultRestoreM = restoreT . restoreM {-# INLINABLE defaultRestoreM #-} -------------------------------------------------------------------------------- -- MonadBaseControl transformer instances -------------------------------------------------------------------------------- #define BODY(T) { \ type StM (T m) a = ComposeSt (T) m a; \ liftBaseWith = defaultLiftBaseWith; \ restoreM = defaultRestoreM; \ {-# INLINABLE liftBaseWith #-}; \ {-# INLINABLE restoreM #-}} #define TRANS( T) \ instance ( MonadBaseControl b m) => MonadBaseControl b (T m) where BODY(T) #define TRANS_CTX(CTX, T) \ instance (CTX, MonadBaseControl b m) => MonadBaseControl b (T m) where BODY(T) TRANS(IdentityT) TRANS(MaybeT) TRANS(ListT) TRANS(ReaderT r) TRANS(Strict.StateT s) TRANS( StateT s) TRANS(ExceptT e) TRANS_CTX(Error e, ErrorT e) TRANS_CTX(Monoid w, Strict.WriterT w) TRANS_CTX(Monoid w, WriterT w) TRANS_CTX(Monoid w, Strict.RWST r w s) TRANS_CTX(Monoid w, RWST r w s) -------------------------------------------------------------------------------- -- * Utility functions -------------------------------------------------------------------------------- -- | An often used composition: @control f = 'liftBaseWith' f >>= 'restoreM'@ control :: MonadBaseControl b m => (RunInBase m b -> b (StM m a)) -> m a control f = liftBaseWith f >>= restoreM {-# INLINABLE control #-} -- | Embed a transformer function as an function in the base monad returning a -- mutated transformer state. embed :: MonadBaseControl b m => (a -> m c) -> m (a -> b (StM m c)) embed f = liftBaseWith $ \runInBase -> return (runInBase . f) {-# INLINABLE embed #-} -- | Performs the same function as 'embed', but discards transformer state -- from the embedded function. embed_ :: MonadBaseControl b m => (a -> m ()) -> m (a -> b ()) embed_ f = liftBaseWith $ \runInBase -> return (void . runInBase . f) {-# INLINABLE embed_ #-} -- | @liftBaseOp@ is a particular application of 'liftBaseWith' that allows -- lifting control operations of type: -- -- @((a -> b c) -> b c)@ to: @('MonadBaseControl' b m => (a -> m c) -> m c)@. -- -- For example: -- -- @liftBaseOp alloca :: 'MonadBaseControl' 'IO' m => (Ptr a -> m c) -> m c@ liftBaseOp :: MonadBaseControl b m => ((a -> b (StM m c)) -> b (StM m d)) -> ((a -> m c) -> m d) liftBaseOp f = \g -> control $ \runInBase -> f $ runInBase . g {-# INLINABLE liftBaseOp #-} -- | @liftBaseOp_@ is a particular application of 'liftBaseWith' that allows -- lifting control operations of type: -- -- @(b a -> b a)@ to: @('MonadBaseControl' b m => m a -> m a)@. -- -- For example: -- -- @liftBaseOp_ mask_ :: 'MonadBaseControl' 'IO' m => m a -> m a@ liftBaseOp_ :: MonadBaseControl b m => (b (StM m a) -> b (StM m c)) -> ( m a -> m c) liftBaseOp_ f = \m -> control $ \runInBase -> f $ runInBase m {-# INLINABLE liftBaseOp_ #-} -- | @liftBaseDiscard@ is a particular application of 'liftBaseWith' that allows -- lifting control operations of type: -- -- @(b () -> b a)@ to: @('MonadBaseControl' b m => m () -> m a)@. -- -- Note that, while the argument computation @m ()@ has access to the captured -- state, all its side-effects in @m@ are discarded. It is run only for its -- side-effects in the base monad @b@. -- -- For example: -- -- @liftBaseDiscard forkIO :: 'MonadBaseControl' 'IO' m => m () -> m ThreadId@ liftBaseDiscard :: MonadBaseControl b m => (b () -> b a) -> (m () -> m a) liftBaseDiscard f = \m -> liftBaseWith $ \runInBase -> f $ void $ runInBase m {-# INLINABLE liftBaseDiscard #-} -- | @liftBaseOpDiscard@ is a particular application of 'liftBaseWith' that allows -- lifting control operations of type: -- -- @((a -> b ()) -> b c)@ to: @('MonadBaseControl' b m => (a -> m ()) -> m c)@. -- -- Note that, while the argument computation @m ()@ has access to the captured -- state, all its side-effects in @m@ are discarded. It is run only for its -- side-effects in the base monad @b@. -- -- For example: -- -- @liftBaseDiscard (runServer addr port) :: 'MonadBaseControl' 'IO' m => m () -> m ()@ liftBaseOpDiscard :: MonadBaseControl b m => ((a -> b ()) -> b c) -> (a -> m ()) -> m c liftBaseOpDiscard f g = liftBaseWith $ \runInBase -> f $ void . runInBase . g {-# INLINABLE liftBaseOpDiscard #-}