@@ -6,7 +6,7 @@
66-- This module is intended for internal use only, and may change without warning
77-- in subsequent releases.
88module Effectful.Internal.Monad
9− ( -- * Monad
9+ ( -- * The 'Eff' monad
1010 Eff
1111 , runPureEff
1212
@@ -22,49 +22,41 @@ module Effectful.Internal.Monad
2222 , IOE
2323 , runEff
2424
25− -- * Primitive
25+ -- * Prim
2626 , Prim
2727 , runPrim
2828
29− -- ** Unlift strategies
29+ -- * Unlift strategies
3030 , UnliftStrategy(..)
3131 , Persistence(..)
3232 , Limit(..)
3333 , unliftStrategy
3434 , withUnliftStrategy
3535 , withEffToIO
36− , UnliftError(..)
3736
38− --- *** Low-level helpers
39− , unsafeLiftMapIO
40− , unsafeUnliftIO
41− , seqUnliftEff
42− , concUnliftEff
37+ -- ** Low-level unlifts
38+ , seqUnliftIO
39+ , concUnliftIO
4340
4441 -- * Effects
4542
46− -- ** Handler
43+ -- ** Dynamic dispatch
4744 , EffectHandler
4845 , LocalEnv(..)
49− , Handler(..)
46+ , HandlerA(..)
5047 , runHandler
51−
52− -- *** Sending operations
5348 , send
5449
55− -- ** Primitive
56−
57− -- *** Running
58− , runEffect
59− , evalEffect
60− , execEffect
61−
62− -- *** Modification
63− , getEffect
64− , putEffect
65− , stateEffect
66− , stateEffectM
67− , localEffect
50+ -- ** Static dispatch
51+ , DataA(..)
52+ , runData
53+ , evalData
54+ , execData
55+ , getData
56+ , putData
57+ , stateData
58+ , stateDataM
59+ , localData
6860 ) where
6961
7062import Control.Applicative (liftA2)
@@ -87,44 +79,43 @@ import Effectful.Internal.Unlift
8779
8880type role Eff nominal representational
8981
90−-- | The 'Eff' monad provides the implementation of an operation that performs
82+-- | The 'Eff' monad provides the implementation of a computation that performs
9183-- an arbitrary set of effects. In @'Eff' es a@, @es@ is a type-level list that
92−-- contains all the effects that the operation may perform. For example, an
93−-- operation that produces an 'Integer' by consuming a 'String' from the global
94−-- environment and acting upon a single mutable cell containing a 'Bool' would
95−-- have the following type:
84+-- contains all the effects that the computation may perform. For example, a
85+-- computation that produces an 'Integer' by consuming a 'String' from the
86+-- global environment and acting upon a single mutable value of type 'Bool'
87+-- would have the following type:
9688--
9789-- @
98−-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.State' 'Bool'] 'Integer'
90+-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.Local.State' 'Bool'] 'Integer'
9991-- @
10092--
10193-- Normally, a concrete list of effects is not used to parameterize 'Eff'.
10294-- Instead, the '(:>)' type class is used to express constraints on the list of
103−-- effects without coupling an operation to a concrete list of effects. For
104−-- example, the above example would more commonly be expressed with the
105−-- following type:
95+-- effects without coupling a computation to a concrete list of effects. For
96+-- example, the above example would be expressed with the following type:
10697--
10798-- @
108−-- ('Effectful.Reader.Reader' 'String' ':>' es, 'Effectful.State.State' 'Bool' ':>' es) => 'Eff' es 'Integer'
99+-- ('Effectful.Reader.Reader' 'String' ':>' es, 'Effectful.State.Local.State' 'Bool' ':>' es) => 'Eff' es 'Integer'
109100-- @
110101--
111−-- This abstraction allows the operation to be used in functions that may
102+-- This abstraction allows the computation to be used in functions that may
112103-- perform other effects, and it also allows the effects to be handled in any
113104-- order.
114105newtype Eff (es :: [Effect]) a = Eff (Env es -> IO a)
115106 deriving (Monoid, Semigroup)
116107
117−-- | Run a pure 'Eff' operation.
108+-- | Run a pure 'Eff' computation.
118109--
119−-- For running operations with side effects see 'runEff'.
110+-- For running computations with side effects see 'runEff'.
120111runPureEff :: Eff '[] a -> a
121112runPureEff (Eff m) =
122− -- unsafePerformIO is safe here since IOE was not on the stack, so no IO with
123− -- side effects was performed (unless someone sneakily introduced side effects
124− -- with unsafeEff, but then all bets are off).
113+ -- unsafeDupablePerformIO is safe here since IOE was not on the stack, so no
114+ -- IO with side effects was performed (unless someone sneakily introduced side
115+ -- effects with unsafeEff, but then all bets are off).
125116 --
126117 -- Moreover, internals don't allocate any resources that require explicit
127− -- cleanup actions to run, so the "Dupable" part should also be just fine.
118+ -- cleanup actions to run.
128119 unsafeDupablePerformIO $ m =<< emptyEnv
129120
130121----------------------------------------
@@ -137,84 +128,29 @@ unEff (Eff m) = m
137128-- | Access the underlying 'IO' monad along with the environment.
138129--
139130-- This function is __unsafe__ because it can be used to introduce arbitrary
140−-- 'IO' actions into pure 'Eff' operations.
131+-- 'IO' actions into pure 'Eff' computations.
141132unsafeEff :: (Env es -> IO a) -> Eff es a
142133unsafeEff m = Eff (oneShot m)
143134
144135-- | Access the underlying 'IO' monad.
145136--
146137-- This function is __unsafe__ because it can be used to introduce arbitrary
147−-- 'IO' actions into pure 'Eff' operations.
138+-- 'IO' actions into pure 'Eff' computations.
148139unsafeEff_ :: IO a -> Eff es a
149140unsafeEff_ m = unsafeEff $ \_ -> m
150141
151−-- | Utility for lifting 'IO' operations of type
152−--
153−-- @'IO' a -> 'IO' b@
154−--
155−-- to
156−--
157−-- @'Eff' es a -> 'Eff' es b@
158−--
159−-- This function is __unsafe__ because:
160−--
161−-- - It can be used to introduce arbitrary 'IO' actions into pure 'Eff'
162−-- operations.
163−--
164−-- - The 'IO' operation must not run its argument in a separate thread, but it's
165−-- not checked anywhere.
166−unsafeLiftMapIO :: (IO a -> IO b) -> Eff es a -> Eff es b
167−unsafeLiftMapIO f m = unsafeEff $ \es -> f (unEff m es)
168−
169−-- | Utility for running 'Eff' computations locally in the 'IO' monad.
170−--
171−-- This function is __unsafe__ because:
172−--
173−-- - It can be used to introduce arbitrary 'IO' actions into pure 'Eff'
174−-- operations.
175−--
176−-- - Unlifted 'Eff' operations must not be run in a thread distinct from the
177−-- caller of 'unsafeUnliftIO', but it's not checked anywhere.
178−unsafeUnliftIO
179− :: HasCallStack
180− => ((forall r. Eff es r -> IO r) -> IO a)
181− -> Eff es a
182−unsafeUnliftIO k = unsafeEff $ \es -> k (`unEff` es)
183−
184142----------------------------------------
185−-- Unlifting Eff
143+-- Unlifting IO
186144
187145-- | Get the current 'UnliftStrategy'.
188146unliftStrategy :: IOE :> es => Eff es UnliftStrategy
189147unliftStrategy = do
190− IdE (IOE unlift) <- getEffect
148+ DataA (IOE unlift) <- getData
191149 pure unlift
192150
193151-- | Locally override the 'UnliftStrategy' with the given value.
194152withUnliftStrategy :: IOE :> es => UnliftStrategy -> Eff es a -> Eff es a
195−withUnliftStrategy unlift = localEffect $ \_ -> IdE (IOE unlift)
196−
197−-- | Lower 'Eff' operations into 'IO' ('SeqUnlift').
198−--
199−-- Exceptions thrown by this function:
200−--
201−-- - 'InvalidUseOfSeqUnlift' if the unlift function is used in another thread.
202−seqUnliftEff
203− :: HasCallStack
204− => Env es
205− -> ((forall r. Eff es r -> IO r) -> IO a)
206− -> IO a
207−seqUnliftEff es k = seqUnliftIO k es unEff
208−
209−-- | Lower 'Eff' operations into 'IO' ('ConcUnlift').
210−concUnliftEff
211− :: HasCallStack
212− => Env es
213− -> Persistence
214− -> Limit
215− -> ((forall r. Eff es r -> IO r) -> IO a)
216− -> IO a
217−concUnliftEff es persistence limit k = concUnliftIO persistence limit k es unEff
153+withUnliftStrategy unlift = localData $ \_ -> DataA (IOE unlift)
218154
219155-- | Create an unlifting function with the current 'UnliftStrategy'.
220156--
@@ -222,16 +158,38 @@ concUnliftEff es persistence limit k = concUnliftIO persistence limit k es unEff
222158-- constraint for accurate stack traces in case an insufficiently powerful
223159-- 'UnliftStrategy' is used and the unlifting function fails.
224160--
225−-- /Note:/ the strategy is reset to 'SeqUnlift' for new threads.
161+-- /Note:/ the strategy is reset to 'SeqUnlift' inside the continuation.
226162withEffToIO
227163 :: (HasCallStack, IOE :> es)
228164 => ((forall r. Eff es r -> IO r) -> IO a)
229165 -- ^ Continuation with the unlifting function in scope.
230166 -> Eff es a
231167withEffToIO f = unliftStrategy >>= \case
232− SeqUnlift -> unsafeEff $ \es -> seqUnliftEff es f
168+ SeqUnlift -> unsafeEff $ \es -> seqUnliftIO es f
233169 ConcUnlift p b -> withUnliftStrategy SeqUnlift $ do
234− unsafeEff $ \es -> concUnliftEff es p b f
170+ unsafeEff $ \es -> concUnliftIO es p b f
171+
172+-- | Create an unlifting function with the 'SeqUnlift' strategy.
173+seqUnliftIO
174+ :: HasCallStack
175+ => Env es
176+ -- ^ The environment.
177+ -> ((forall r. Eff es r -> IO r) -> IO a)
178+ -- ^ Continuation with the unlifting function in scope.
179+ -> IO a
180+seqUnliftIO es k = seqUnlift k es unEff
181+
182+-- | Create an unlifting function with the 'ConcUnlift' strategy.
183+concUnliftIO
184+ :: HasCallStack
185+ => Env es
186+ -- ^ The environment.
187+ -> Persistence
188+ -> Limit
189+ -> ((forall r. Eff es r -> IO r) -> IO a)
190+ -- ^ Continuation with the unlifting function in scope.
191+ -> IO a
192+concUnliftIO es persistence limit k = concUnlift persistence limit k es unEff
235193
236194----------------------------------------
237195-- Base
@@ -300,15 +258,15 @@ instance Fail :> es => MonadFail (Eff es) where
300258----------------------------------------
301259-- IO
302260
303−-- | Run arbitrary 'IO' operations via 'MonadIO' or 'MonadUnliftIO'.
261+-- | Run arbitrary 'IO' computations via 'MonadIO' or 'MonadUnliftIO'.
304262newtype IOE :: Effect where
305263 IOE :: UnliftStrategy -> IOE m r
306264
307−-- | Run an 'Eff' operation with side effects.
265+-- | Run an 'Eff' computation with side effects.
308266--
309−-- For running pure operations see 'runPureEff'.
267+-- For running pure computations see 'runPureEff'.
310268runEff :: Eff '[IOE] a -> IO a
311−runEff m = unEff (evalEffect (IdE (IOE SeqUnlift)) m) =<< emptyEnv
269+runEff m = unEff (evalData (DataA (IOE SeqUnlift)) m) =<< emptyEnv
312270
313271instance IOE :> es => MonadIO (Eff es) where
314272 liftIO = unsafeEff_
@@ -332,20 +290,20 @@ instance IOE :> es => MonadBaseControl IO (Eff es) where
332290----------------------------------------
333291-- Primitive
334292
335−-- | An effect to perform primitive state-transformer actions.
293+-- | Provide the ability to perform primitive state-transformer actions.
336294data Prim :: Effect where
337295 Prim :: Prim m r
338296
339−-- | Run an 'Eff' operation with primitive state-transformer actions.
297+-- | Run an 'Eff' computation with primitive state-transformer actions.
340298runPrim :: IOE :> es => Eff (Prim : es) a -> Eff es a
341−runPrim = evalEffect (IdE Prim)
299+runPrim = evalData (DataA Prim)
342300
343301instance Prim :> es => PrimMonad (Eff es) where
344302 type PrimState (Eff es) = RealWorld
345303 primitive = unsafeEff_ . IO
346304
347305----------------------------------------
348−-- Handler
306+-- Dynamic dispatch
349307
350308type role LocalEnv nominal nominal
351309
@@ -361,76 +319,97 @@ newtype LocalEnv (localEs :: [Effect]) (handlerEs :: [Effect]) = LocalEnv (Env l
361319type EffectHandler e es
362320 = forall a localEs. HasCallStack
363321 => LocalEnv localEs es
364− -- ^ Capture of the local environment for handling local 'Eff' operations when
365− -- @e@ is a higher order effect.
322+ -- ^ Capture of the local environment for handling local 'Eff' computations
323+ -- when @e@ is a higher order effect.
366324 -> e (Eff localEs) a
367325 -- ^ The effect performed in the local environment.
368326 -> Eff es a
369327
370−-- | An effect handler bundled along with its environment.
371−data Handler :: Effect -> Type where
372− Handler :: !(Env es) -> !(EffectHandler e es) -> Handler e
328+-- | An adapter for dynamically dispatched effects.
329+--
330+-- Represents the effect handler bundled with its environment.
331+data HandlerA :: Effect -> Type where
332+ HandlerA :: !(Env es) -> !(EffectHandler e es) -> HandlerA e
373333
374−-- | Run the effect with the given handler.
375−runHandler :: Handler e -> Eff (e : es) a -> Eff es a
334+-- | Run a dynamically dispatched effect with the given handler.
335+runHandler :: HandlerA e -> Eff (e : es) a -> Eff es a
376336runHandler e m = unsafeEff $ \es0 -> do
377337 size0 <- sizeEnv es0
378338 E.bracket (unsafeConsEnv e relinker es0)
379339 (unsafeTailEnv size0)
380340 (\es -> unEff m es)
381341 where
382− relinker :: Relinker Handler e
383− relinker = Relinker $ \relink (Handler env handle) -> do
384− newEnv <- relink env
385− pure $ Handler newEnv handle
342+ relinker :: Relinker HandlerA e
343+ relinker = Relinker $ \relink (HandlerA handlerEs handle) -> do
344+ newHandlerEs <- relink handlerEs
345+ pure $ HandlerA newHandlerEs handle
386346
387347-- | Send an operation of the given effect to its handler for execution.
388348send :: (HasCallStack, e :> es) => e (Eff es) a -> Eff es a
389349send op = unsafeEff $ \es -> do
390− Handler env handle <- getEnv es
391− unEff (handle (LocalEnv es) op) env
350+ HandlerA handlerEs handle <- getEnv es
351+ unEff (handle (LocalEnv es) op) handlerEs
392352
393353----------------------------------------
394−-- Helpers
354+-- Static dispatch
395355
396−runEffect :: handler e -> Eff (e : es) a -> Eff es (a, handler e)
397−runEffect e0 m = unsafeEff $ \es0 -> do
356+-- | An adapter for statically dispatched effects.
357+--
358+-- Represents an arbitrary data type with the appropriate number of phantom type
359+-- parameters.
360+newtype DataA :: Effect -> Type where
361+ DataA :: (forall m r. e m r) -> DataA e
362+
363+-- | Run a statically dispatched effect with the given initial state and return
364+-- the final value along with the final state.
365+runData :: DataA e -> Eff (e : es) a -> Eff es (a, DataA e)
366+runData e0 m = unsafeEff $ \es0 -> do
398367 size0 <- sizeEnv es0
399368 E.bracket (unsafeConsEnv e0 noRelinker es0)
400369 (unsafeTailEnv size0)
401370 (\es -> (,) <$> unEff m es <*> getEnv es)
402371
403−evalEffect :: handler e -> Eff (e : es) a -> Eff es a
404−evalEffect e m = unsafeEff $ \es0 -> do
372+-- | Run a statically dispatched effect with the given initial state and return
373+-- the final value, discarding the final state.
374+evalData :: DataA e -> Eff (e : es) a -> Eff es a
375+evalData e m = unsafeEff $ \es0 -> do
405376 size0 <- sizeEnv es0
406377 E.bracket (unsafeConsEnv e noRelinker es0)
407378 (unsafeTailEnv size0)
408379 (\es -> unEff m es)
409380
410−execEffect :: handler e -> Eff (e : es) a -> Eff es (handler e)
411−execEffect e0 m = unsafeEff $ \es0 -> do
381+-- | Run a statically dispatched effect with the given initial state and return
382+-- the final state, discarding the final value.
383+execData :: DataA e -> Eff (e : es) a -> Eff es (DataA e)
384+execData e0 m = unsafeEff $ \es0 -> do
412385 size0 <- sizeEnv es0
413386 E.bracket (unsafeConsEnv e0 noRelinker es0)
414387 (unsafeTailEnv size0)
415388 (\es -> unEff m es *> getEnv es)
416389
417−getEffect :: e :> es => Eff es (handler e)
418−getEffect = unsafeEff $ \es -> getEnv es
390+-- | Fetch the current state of the effect.
391+getData :: e :> es => Eff es (DataA e)
392+getData = unsafeEff $ \es -> getEnv es
419393
420−putEffect :: e :> es => handler e -> Eff es ()
421−putEffect e = unsafeEff $ \es -> putEnv es e
394+-- | Set the current state of the effect to the given value.
395+putData :: e :> es => DataA e -> Eff es ()
396+putData e = unsafeEff $ \es -> putEnv es e
422397
423−stateEffect :: e :> es => (handler e -> (a, handler e)) -> Eff es a
424−stateEffect f = unsafeEff $ \es -> stateEnv es f
398+-- | Apply the function to the current state of the effect and return a value.
399+stateData :: e :> es => (DataA e -> (a, DataA e)) -> Eff es a
400+stateData f = unsafeEff $ \es -> stateEnv es f
425401
426−stateEffectM :: e :> es => (handler e -> Eff es (a, handler e)) -> Eff es a
427−stateEffectM f = unsafeEff $ \es -> E.mask $ \release -> do
402+-- | Apply the monadic function to the current state of the effect and return a
403+-- value.
404+stateDataM :: e :> es => (DataA e -> Eff es (a, DataA e)) -> Eff es a
405+stateDataM f = unsafeEff $ \es -> E.mask $ \release -> do
428406 (a, e) <- (\e -> release $ unEff (f e) es) =<< getEnv es
429407 putEnv es e
430408 pure a
431409
432−localEffect :: e :> es => (handler e -> handler e) -> Eff es a -> Eff es a
433−localEffect f m = unsafeEff $ \es -> do
410+-- | Execute a computation with a temporarily modified state of the effect.
411+localData :: e :> es => (DataA e -> DataA e) -> Eff es a -> Eff es a
412+localData f m = unsafeEff $ \es -> do
434413 E.bracket (stateEnv es $ \e -> (e, f e))
435414 (\e -> putEnv es e)
436415 (\_ -> unEff m es)