@@ -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
@@ -22,48 +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− , seqUnliftEff
41− , concUnliftEff
37+ -- ** Low-level unlifts
38+ , seqUnliftIO
39+ , concUnliftIO
4240
4341 -- * Effects
4442
45− -- ** Handler
43+ -- ** Dynamic dispatch
4644 , EffectHandler
4745 , LocalEnv(..)
48− , Handler(..)
46+ , HandlerA(..)
4947 , runHandler
50−
51− -- *** Sending operations
5248 , send
5349
54− -- ** Primitive
55−
56− -- *** Running
57− , runEffect
58− , evalEffect
59− , execEffect
60−
61− -- *** Modification
62− , getEffect
63− , putEffect
64− , stateEffect
65− , stateEffectM
66− , localEffect
50+ -- ** Static dispatch
51+ , DataA(..)
52+ , runData
53+ , evalData
54+ , execData
55+ , getData
56+ , putData
57+ , stateData
58+ , stateDataM
59+ , localData
6760 ) where
6861
6962import Control.Applicative (liftA2)
@@ -86,44 +79,43 @@ import Effectful.Internal.Unlift
8679
8780type role Eff nominal representational
8881
89−-- | The 'Eff' monad provides the implementation of an operation that performs
82+-- | The 'Eff' monad provides the implementation of a computation that performs
9083-- an arbitrary set of effects. In @'Eff' es a@, @es@ is a type-level list that
91−-- contains all the effects that the operation may perform. For example, an
92−-- operation that produces an 'Integer' by consuming a 'String' from the global
93−-- environment and acting upon a single mutable cell containing a 'Bool' would
94−-- 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:
9588--
9689-- @
97−-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.State' 'Bool'] 'Integer'
90+-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.Local.State' 'Bool'] 'Integer'
9891-- @
9992--
10093-- Normally, a concrete list of effects is not used to parameterize 'Eff'.
10194-- Instead, the '(:>)' type class is used to express constraints on the list of
102−-- effects without coupling an operation to a concrete list of effects. For
103−-- example, the above example would more commonly be expressed with the
104−-- 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:
10597--
10698-- @
107−-- ('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'
108100-- @
109101--
110−-- 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
111103-- perform other effects, and it also allows the effects to be handled in any
112104-- order.
113105newtype Eff (es :: [Effect]) a = Eff (Env es -> IO a)
114106 deriving (Monoid, Semigroup)
115107
116−-- | Run a pure 'Eff' operation.
108+-- | Run a pure 'Eff' computation.
117109--
118−-- For running operations with side effects see 'runEff'.
110+-- For running computations with side effects see 'runEff'.
119111runPureEff :: Eff '[] a -> a
120112runPureEff (Eff m) =
121− -- unsafePerformIO is safe here since IOE was not on the stack, so no IO with
122− -- side effects was performed (unless someone sneakily introduced side effects
123− -- 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).
124116 --
125117 -- Moreover, internals don't allocate any resources that require explicit
126− -- cleanup actions to run, so the "Dupable" part should also be just fine.
118+ -- cleanup actions to run.
127119 unsafeDupablePerformIO $ m =<< emptyEnv
128120
129121----------------------------------------
@@ -136,69 +128,29 @@ unEff (Eff m) = m
136128-- | Access the underlying 'IO' monad along with the environment.
137129--
138130-- This function is __unsafe__ because it can be used to introduce arbitrary
139−-- 'IO' actions into pure 'Eff' operations.
131+-- 'IO' actions into pure 'Eff' computations.
140132unsafeEff :: (Env es -> IO a) -> Eff es a
141133unsafeEff m = Eff (oneShot m)
142134
143135-- | Access the underlying 'IO' monad.
144136--
145137-- This function is __unsafe__ because it can be used to introduce arbitrary
146−-- 'IO' actions into pure 'Eff' operations.
138+-- 'IO' actions into pure 'Eff' computations.
147139unsafeEff_ :: IO a -> Eff es a
148140unsafeEff_ m = unsafeEff $ \_ -> m
149141
150−-- | Utility for lifting 'IO' operations of type
151−--
152−-- @'IO' a -> 'IO' b@
153−--
154−-- to
155−--
156−-- @'Eff' es a -> 'Eff' es b@
157−--
158−-- This function is __unsafe__ because:
159−--
160−-- - It can be used to introduce arbitrary 'IO' actions into pure 'Eff'
161−-- operations.
162−--
163−-- - The 'IO' operation must not run its argument in a separate thread, but it's
164−-- not checked anywhere.
165−unsafeLiftMapIO :: (IO a -> IO b) -> Eff es a -> Eff es b
166−unsafeLiftMapIO f m = unsafeEff $ \es -> f (unEff m es)
167−
168142----------------------------------------
169−-- Unlifting Eff
143+-- Unlifting IO
170144
171145-- | Get the current 'UnliftStrategy'.
172146unliftStrategy :: IOE :> es => Eff es UnliftStrategy
173147unliftStrategy = do
174− IdE (IOE unlift) <- getEffect
148+ DataA (IOE unlift) <- getData
175149 pure unlift
176150
177151-- | Locally override the 'UnliftStrategy' with the given value.
178152withUnliftStrategy :: IOE :> es => UnliftStrategy -> Eff es a -> Eff es a
179−withUnliftStrategy unlift = localEffect $ \_ -> IdE (IOE unlift)
180−
181−-- | Lower 'Eff' operations into 'IO' ('SeqUnlift').
182−--
183−-- Exceptions thrown by this function:
184−--
185−-- - 'InvalidUseOfSeqUnlift' if the unlift function is used in another thread.
186−seqUnliftEff
187− :: HasCallStack
188− => Env es
189− -> ((forall r. Eff es r -> IO r) -> IO a)
190− -> IO a
191−seqUnliftEff es k = seqUnliftIO k es unEff
192−
193−-- | Lower 'Eff' operations into 'IO' ('ConcUnlift').
194−concUnliftEff
195− :: HasCallStack
196− => Env es
197− -> Persistence
198− -> Limit
199− -> ((forall r. Eff es r -> IO r) -> IO a)
200− -> IO a
201−concUnliftEff es persistence limit k = concUnliftIO persistence limit k es unEff
153+withUnliftStrategy unlift = localData $ \_ -> DataA (IOE unlift)
202154
203155-- | Create an unlifting function with the current 'UnliftStrategy'.
204156--
@@ -206,16 +158,38 @@ concUnliftEff es persistence limit k = concUnliftIO persistence limit k es unEff
206158-- constraint for accurate stack traces in case an insufficiently powerful
207159-- 'UnliftStrategy' is used and the unlifting function fails.
208160--
209−-- /Note:/ the strategy is reset to 'SeqUnlift' for new threads.
161+-- /Note:/ the strategy is reset to 'SeqUnlift' inside the continuation.
210162withEffToIO
211163 :: (HasCallStack, IOE :> es)
212164 => ((forall r. Eff es r -> IO r) -> IO a)
213165 -- ^ Continuation with the unlifting function in scope.
214166 -> Eff es a
215167withEffToIO f = unliftStrategy >>= \case
216− SeqUnlift -> unsafeEff $ \es -> seqUnliftEff es f
168+ SeqUnlift -> unsafeEff $ \es -> seqUnliftIO es f
217169 ConcUnlift p b -> withUnliftStrategy SeqUnlift $ do
218− 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
219193
220194----------------------------------------
221195-- Base
@@ -284,15 +258,15 @@ instance Fail :> es => MonadFail (Eff es) where
284258----------------------------------------
285259-- IO
286260
287−-- | Run arbitrary 'IO' operations via 'MonadIO' or 'MonadUnliftIO'.
261+-- | Run arbitrary 'IO' computations via 'MonadIO' or 'MonadUnliftIO'.
288262newtype IOE :: Effect where
289263 IOE :: UnliftStrategy -> IOE m r
290264
291−-- | Run an 'Eff' operation with side effects.
265+-- | Run an 'Eff' computation with side effects.
292266--
293−-- For running pure operations see 'runPureEff'.
267+-- For running pure computations see 'runPureEff'.
294268runEff :: Eff '[IOE] a -> IO a
295−runEff m = unEff (evalEffect (IdE (IOE SeqUnlift)) m) =<< emptyEnv
269+runEff m = unEff (evalData (DataA (IOE SeqUnlift)) m) =<< emptyEnv
296270
297271instance IOE :> es => MonadIO (Eff es) where
298272 liftIO = unsafeEff_
@@ -316,20 +290,20 @@ instance IOE :> es => MonadBaseControl IO (Eff es) where
316290----------------------------------------
317291-- Primitive
318292
319−-- | An effect to perform primitive state-transformer actions.
293+-- | Provide the ability to perform primitive state-transformer actions.
320294data Prim :: Effect where
321295 Prim :: Prim m r
322296
323−-- | Run an 'Eff' operation with primitive state-transformer actions.
297+-- | Run an 'Eff' computation with primitive state-transformer actions.
324298runPrim :: IOE :> es => Eff (Prim : es) a -> Eff es a
325−runPrim = evalEffect (IdE Prim)
299+runPrim = evalData (DataA Prim)
326300
327301instance Prim :> es => PrimMonad (Eff es) where
328302 type PrimState (Eff es) = RealWorld
329303 primitive = unsafeEff_ . IO
330304
331305----------------------------------------
332−-- Handler
306+-- Dynamic dispatch
333307
334308type role LocalEnv nominal nominal
335309
@@ -345,76 +319,97 @@ newtype LocalEnv (localEs :: [Effect]) (handlerEs :: [Effect]) = LocalEnv (Env l
345319type EffectHandler e es
346320 = forall a localEs. HasCallStack
347321 => LocalEnv localEs es
348− -- ^ Capture of the local environment for handling local 'Eff' operations when
349− -- @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.
350324 -> e (Eff localEs) a
351325 -- ^ The effect performed in the local environment.
352326 -> Eff es a
353327
354−-- | An effect handler bundled along with its environment.
355−data Handler :: Effect -> Type where
356− 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
357333
358−-- | Run the effect with the given handler.
359−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
360336runHandler e m = unsafeEff $ \es0 -> do
361337 size0 <- sizeEnv es0
362338 E.bracket (unsafeConsEnv e relinker es0)
363339 (unsafeTailEnv size0)
364340 (\es -> unEff m es)
365341 where
366− relinker :: Relinker Handler e
367− relinker = Relinker $ \relink (Handler env handle) -> do
368− newEnv <- relink env
369− 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
370346
371347-- | Send an operation of the given effect to its handler for execution.
372348send :: (HasCallStack, e :> es) => e (Eff es) a -> Eff es a
373349send op = unsafeEff $ \es -> do
374− Handler env handle <- getEnv es
375− unEff (handle (LocalEnv es) op) env
350+ HandlerA handlerEs handle <- getEnv es
351+ unEff (handle (LocalEnv es) op) handlerEs
376352
377353----------------------------------------
378−-- Helpers
354+-- Static dispatch
379355
380−runEffect :: handler e -> Eff (e : es) a -> Eff es (a, handler e)
381−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
382367 size0 <- sizeEnv es0
383368 E.bracket (unsafeConsEnv e0 noRelinker es0)
384369 (unsafeTailEnv size0)
385370 (\es -> (,) <$> unEff m es <*> getEnv es)
386371
387−evalEffect :: handler e -> Eff (e : es) a -> Eff es a
388−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
389376 size0 <- sizeEnv es0
390377 E.bracket (unsafeConsEnv e noRelinker es0)
391378 (unsafeTailEnv size0)
392379 (\es -> unEff m es)
393380
394−execEffect :: handler e -> Eff (e : es) a -> Eff es (handler e)
395−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
396385 size0 <- sizeEnv es0
397386 E.bracket (unsafeConsEnv e0 noRelinker es0)
398387 (unsafeTailEnv size0)
399388 (\es -> unEff m es *> getEnv es)
400389
401−getEffect :: e :> es => Eff es (handler e)
402−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
403393
404−putEffect :: e :> es => handler e -> Eff es ()
405−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
406397
407−stateEffect :: e :> es => (handler e -> (a, handler e)) -> Eff es a
408−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
409401
410−stateEffectM :: e :> es => (handler e -> Eff es (a, handler e)) -> Eff es a
411−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
412406 (a, e) <- (\e -> release $ unEff (f e) es) =<< getEnv es
413407 putEnv es e
414408 pure a
415409
416−localEffect :: e :> es => (handler e -> handler e) -> Eff es a -> Eff es a
417−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
418413 E.bracket (stateEnv es $ \e -> (e, f e))
419414 (\e -> putEnv es e)
420415 (\_ -> unEff m es)