@@ -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
@@ -16,18 +16,17 @@ module Effectful.Internal.Monad
1616 , unsafeEff_
1717
1818 -- * Fail
19− , Fail
20− , runFail
19+ , Fail(..)
2120
2221 -- * IO
2322 , IOE
2423 , runEff
2524
26− -- * Primitive
25+ -- * Prim
2726 , Prim
2827 , runPrim
2928
30− -- ** Unlift strategies
29+ -- * Unlift strategies
3130 , UnliftStrategy(..)
3231 , Persistence(..)
3332 , Limit(..)
@@ -35,87 +34,88 @@ module Effectful.Internal.Monad
3534 , withUnliftStrategy
3635 , withEffToIO
3736
38− --- *** Low-level helpers
39− , unsafeWithLiftMapIO
40− , seqUnliftEff
41− , concUnliftEff
42−
43− -- * Primitive effects
44−
45− -- ** Running
46− , runEffect
47− , evalEffect
48− , execEffect
49−
50− -- ** Modification
51− , getEffect
52− , putEffect
53− , stateEffect
54− , stateEffectM
55− , localEffect
37+ -- ** Low-level unlifts
38+ , seqUnliftIO
39+ , concUnliftIO
40+
41+ -- * Effects
42+
43+ -- ** Dynamic dispatch
44+ , EffectHandler
45+ , LocalEnv(..)
46+ , HandlerA(..)
47+ , runHandler
48+ , send
49+
50+ -- ** Static dispatch
51+ , DataA(..)
52+ , runData
53+ , evalData
54+ , execData
55+ , getData
56+ , putData
57+ , stateData
58+ , stateDataM
59+ , localData
5660 ) where
5761
5862import Control.Applicative (liftA2)
59−import Control.Concurrent (myThreadId)
60−import Control.Exception
6163import Control.Monad.Base
6264import Control.Monad.Fix
6365import Control.Monad.IO.Class
6466import Control.Monad.IO.Unlift
6567import Control.Monad.Primitive
6668import Control.Monad.Trans.Control
67−import Data.Unique
6869import GHC.Exts (oneShot)
6970import GHC.IO (IO(..))
7071import GHC.Stack (HasCallStack)
7172import System.IO.Unsafe (unsafeDupablePerformIO)
72−import qualified Control.Monad.Catch as E
73+import qualified Control.Exception as E
74+import qualified Control.Monad.Catch as C
7375
7476import Effectful.Internal.Effect
7577import Effectful.Internal.Env
7678import Effectful.Internal.Unlift
77−import Effectful.Internal.Utils
7879
7980type role Eff nominal representational
8081
81−-- | The 'Eff' monad provides the implementation of an operation that performs
82+-- | The 'Eff' monad provides the implementation of a computation that performs
8283-- an arbitrary set of effects. In @'Eff' es a@, @es@ is a type-level list that
83−-- contains all the effects that the operation may perform. For example, an
84−-- operation that produces an 'Integer' by consuming a 'String' from the global
85−-- environment and acting upon a single mutable cell containing a 'Bool' would
86−-- 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:
8788--
8889-- @
89−-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.State' 'Bool'] 'Integer'
90+-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.Local.State' 'Bool'] 'Integer'
9091-- @
9192--
9293-- Normally, a concrete list of effects is not used to parameterize 'Eff'.
9394-- Instead, the '(:>)' type class is used to express constraints on the list of
94−-- effects without coupling an operation to a concrete list of effects. For
95−-- example, the above example would more commonly be expressed with the
96−-- 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:
9797--
9898-- @
99−-- ('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'
100100-- @
101101--
102−-- 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
103103-- perform other effects, and it also allows the effects to be handled in any
104104-- order.
105105newtype Eff (es :: [Effect]) a = Eff (Env es -> IO a)
106106 deriving (Monoid, Semigroup)
107107
108−-- | Run a pure 'Eff' operation.
108+-- | Run a pure 'Eff' computation.
109109--
110−-- For running operations with side effects see 'runEff'.
110+-- For running computations with side effects see 'runEff'.
111111runPureEff :: Eff '[] a -> a
112112runPureEff (Eff m) =
113− -- unsafePerformIO is safe here since IOE was not on the stack, so no IO with
114− -- side effects was performed (unless someone sneakily introduced side effects
115− -- 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).
116116 --
117117 -- Moreover, internals don't allocate any resources that require explicit
118− -- cleanup actions to run, so the "Dupable" part should also be just fine.
118+ -- cleanup actions to run.
119119 unsafeDupablePerformIO $ m =<< emptyEnv
120120
121121----------------------------------------
@@ -128,69 +128,68 @@ unEff (Eff m) = m
128128-- | Access the underlying 'IO' monad along with the environment.
129129--
130130-- This function is __unsafe__ because it can be used to introduce arbitrary
131−-- 'IO' actions into pure 'Eff' operations.
131+-- 'IO' actions into pure 'Eff' computations.
132132unsafeEff :: (Env es -> IO a) -> Eff es a
133133unsafeEff m = Eff (oneShot m)
134134
135135-- | Access the underlying 'IO' monad.
136136--
137137-- This function is __unsafe__ because it can be used to introduce arbitrary
138−-- 'IO' actions into pure 'Eff' operations.
138+-- 'IO' actions into pure 'Eff' computations.
139139unsafeEff_ :: IO a -> Eff es a
140140unsafeEff_ m = unsafeEff $ \_ -> m
141141
142−-- | Utility for lifting 'IO' operations of type
143−--
144−-- @'IO' a -> 'IO' b@
145−--
146−-- to
147−--
148−-- @forall localEs. 'Eff' localEs a -> 'Eff' localEs b@
142+----------------------------------------
143+-- Unlifting IO
144+
145+-- | Get the current 'UnliftStrategy'.
146+unliftStrategy :: IOE :> es => Eff es UnliftStrategy
147+unliftStrategy = do
148+ DataA (IOE unlift) <- getData
149+ pure unlift
150+
151+-- | Locally override the 'UnliftStrategy' with the given value.
152+withUnliftStrategy :: IOE :> es => UnliftStrategy -> Eff es a -> Eff es a
153+withUnliftStrategy unlift = localData $ \_ -> DataA (IOE unlift)
154+
155+-- | Create an unlifting function with the current 'UnliftStrategy'.
149156--
150−-- This function is __unsafe__ because it can be used to introduce arbitrary
151−-- 'IO' actions into pure 'Eff' operations.
157+-- This function is equivalent to 'withRunInIO', but has a 'HasCallStack'
158+-- constraint for accurate stack traces in case an insufficiently powerful
159+-- 'UnliftStrategy' is used and the unlifting function fails.
152160--
153−-- /Note:/ the 'IO' operation must not run its argument in a separate thread,
154−-- attempting to do so will result in a runtime error.
155−unsafeWithLiftMapIO
156− :: HasCallStack
157− => ((forall a b localEs. (IO a -> IO b) -> Eff localEs a -> Eff localEs b) -> Eff es r)
158− -> Eff es r
159−unsafeWithLiftMapIO k = k $ \mapIO m -> unsafeEff $ \es -> do
160− seqUnliftEff es $ \unlift -> mapIO $ unlift m
161+-- /Note:/ the strategy is reset to 'SeqUnlift' inside the continuation.
162+withEffToIO
163+ :: (HasCallStack, IOE :> es)
164+ => ((forall r. Eff es r -> IO r) -> IO a)
165+ -- ^ Continuation with the unlifting function in scope.
166+ -> Eff es a
167+withEffToIO f = unliftStrategy >>= \case
168+ SeqUnlift -> unsafeEff $ \es -> seqUnliftIO es f
169+ ConcUnlift p b -> withUnliftStrategy SeqUnlift $ do
170+ unsafeEff $ \es -> concUnliftIO es p b f
161171
162−-- | Lower 'Eff' operations into 'IO' ('SeqUnlift').
163−seqUnliftEff
172+-- | Create an unlifting function with the 'SeqUnlift' strategy.
173+seqUnliftIO
164174 :: HasCallStack
165175 => Env es
176+ -- ^ The environment.
166177 -> ((forall r. Eff es r -> IO r) -> IO a)
178+ -- ^ Continuation with the unlifting function in scope.
167179 -> IO a
168−seqUnliftEff es k = do
169− tid0 <- myThreadId
170− k $ \m -> do
171− tid <- myThreadId
172− if tid `eqThreadId` tid0
173− then unEff m es
174− else error
175− $ "If you want to use the unlifting function to run Eff operations "
176− ++ "in multiple threads, have a look at UnliftStrategy (ConcUnlift)."
177−
178−-- | Lower 'Eff' operations into 'IO' ('ConcUnlift').
179−concUnliftEff
180+seqUnliftIO es k = seqUnlift k es unEff
181+
182+-- | Create an unlifting function with the 'ConcUnlift' strategy.
183+concUnliftIO
180184 :: HasCallStack
181185 => Env es
186+ -- ^ The environment.
182187 -> Persistence
183188 -> Limit
184189 -> ((forall r. Eff es r -> IO r) -> IO a)
190+ -- ^ Continuation with the unlifting function in scope.
185191 -> IO a
186−concUnliftEff es Ephemeral (Limited uses) k =
187− ephemeralConcUnliftIO uses k es unEff
188−concUnliftEff es Ephemeral Unlimited k =
189− ephemeralConcUnliftIO maxBound k es unEff
190−concUnliftEff es Persistent (Limited threads) k =
191− persistentConcUnliftIO False threads k es unEff
192−concUnliftEff es Persistent Unlimited k =
193− persistentConcUnliftIO True maxBound k es unEff
192+concUnliftIO es persistence limit k = concUnlift persistence limit k es unEff
194193
195194----------------------------------------
196195-- Base
@@ -218,84 +217,56 @@ instance MonadFix (Eff es) where
218217----------------------------------------
219218-- Exception
220219
221−instance E.MonadThrow (Eff es) where
222− throwM = unsafeEff_ . throwIO
220+instance C.MonadThrow (Eff es) where
221+ throwM = unsafeEff_ . E.throwIO
223222
224−instance E.MonadCatch (Eff es) where
223+instance C.MonadCatch (Eff es) where
225224 catch m handler = unsafeEff $ \es -> do
226225 size <- sizeEnv es
227− unEff m es `catch` \e -> do
226+ unEff m es `E.catch` \e -> do
228227 checkSizeEnv size es
229228 unEff (handler e) es
230229
231−instance E.MonadMask (Eff es) where
232− mask k = unsafeEff $ \es -> mask $ \restore ->
230+instance C.MonadMask (Eff es) where
231+ mask k = unsafeEff $ \es -> E.mask $ \restore ->
233232 unEff (k $ \m -> unsafeEff $ restore . unEff m) es
234233
235− uninterruptibleMask k = unsafeEff $ \es -> uninterruptibleMask $ \restore ->
234+ uninterruptibleMask k = unsafeEff $ \es -> E.uninterruptibleMask $ \restore ->
236235 unEff (k $ \m -> unsafeEff $ restore . unEff m) es
237236
238− generalBracket acquire release use = unsafeEff $ \es -> mask $ \restore -> do
237+ generalBracket acquire release use = unsafeEff $ \es -> E.mask $ \restore -> do
239238 size <- sizeEnv es
240239 resource <- unEff acquire es
241− b <- restore (unEff (use resource) es) `catch` \e -> do
240+ b <- restore (unEff (use resource) es) `E.catch` \e -> do
242241 checkSizeEnv size es
243− _ <- unEff (release resource $ E.ExitCaseException e) es
244− throwIO e
242+ _ <- unEff (release resource $ C.ExitCaseException e) es
243+ E.throwIO e
245244 checkSizeEnv size es
246− c <- unEff (release resource $ E.ExitCaseSuccess b) es
245+ c <- unEff (release resource $ C.ExitCaseSuccess b) es
247246 pure (b, c)
248247
249248----------------------------------------
250249-- Fail
251250
252−newtype Fail :: Effect where
253− Fail :: Unique -> Fail m r
254−
255−runFail :: Eff (Fail : es) a -> Eff es (Either String a)
256−runFail m = unsafeEff $ \es0 -> mask $ \release -> do
257− -- A unique tag is picked so that different runFail handlers don't catch each
258− -- other's exceptions.
259− tag <- newUnique
260− size0 <- sizeEnv es0
261− es <- unsafeConsEnv (IdE (Fail tag)) noRelinker es0
262− r <- tryFailIO tag (release $ unEff m es) `onException` unsafeTailEnv size0 es
263− unsafeTailEnv size0 es
264− pure r
251+-- | Provide the ability to use the 'MonadFail' instance of 'Eff'.
252+data Fail :: Effect where
253+ Fail :: String -> Fail m a
265254
266255instance Fail :> es => MonadFail (Eff es) where
267− fail msg = do
268− IdE (Fail tag) <- getEffect
269− unsafeEff_ . throwIO $ FailEx tag msg
270−
271−--------------------
272−
273−data FailEx = FailEx !Unique String
274−instance Show FailEx where
275− showsPrec p (FailEx _ msg)
276− = ("Effectful.Internal.Monad.FailEx " ++)
277− . showsPrec p msg
278−instance Exception FailEx
279−
280−tryFailIO :: Unique -> IO a -> IO (Either String a)
281−tryFailIO tag m =
282− (Right <$> m) `catch` \err@(FailEx etag msg) -> do
283− if tag == etag
284− then pure $ Left msg
285− else throwIO err
256+ fail = send . Fail
286257
287258----------------------------------------
288259-- IO
289260
290−-- | Run arbitrary 'IO' operations via 'MonadIO' or 'MonadUnliftIO'.
261+-- | Run arbitrary 'IO' computations via 'MonadIO' or 'MonadUnliftIO'.
291262newtype IOE :: Effect where
292263 IOE :: UnliftStrategy -> IOE m r
293264
294−-- | Run an 'Eff' operation with side effects.
265+-- | Run an 'Eff' computation with side effects.
295266--
296−-- For running pure operations see 'runPureEff'.
267+-- For running pure computations see 'runPureEff'.
297268runEff :: Eff '[IOE] a -> IO a
298−runEff m = unEff (evalEffect (IdE (IOE SeqUnlift)) m) =<< emptyEnv
269+runEff m = unEff (evalData (DataA (IOE SeqUnlift)) m) =<< emptyEnv
299270
300271instance IOE :> es => MonadIO (Eff es) where
301272 liftIO = unsafeEff_
@@ -319,141 +290,126 @@ instance IOE :> es => MonadBaseControl IO (Eff es) where
319290----------------------------------------
320291-- Primitive
321292
322−-- | An effect to perform primitive state-transformer actions.
293+-- | Provide the ability to perform primitive state-transformer actions.
323294data Prim :: Effect where
324295 Prim :: Prim m r
325296
326−-- | Run an 'Eff' operation with primitive state-transformer actions.
297+-- | Run an 'Eff' computation with primitive state-transformer actions.
327298runPrim :: IOE :> es => Eff (Prim : es) a -> Eff es a
328−runPrim = evalEffect (IdE Prim)
299+runPrim = evalData (DataA Prim)
329300
330301instance Prim :> es => PrimMonad (Eff es) where
331302 type PrimState (Eff es) = RealWorld
332303 primitive = unsafeEff_ . IO
333304
334305----------------------------------------
335−-- Unlift strategies
336−
337−-- | The strategy to use when unlifting 'Eff' operations via 'withRunInIO' or
338−-- the 'Effectful.Interpreter.localUnlift' family.
339−data UnliftStrategy
340− = SeqUnlift
341− -- ^ The fastest strategy and a default setting for 'IOE'. An attempt to call
342− -- the unlifting function in threads distinct from its creator will result in
343− -- a runtime error.
344− | ConcUnlift !Persistence !Limit
345− -- ^ A strategy that makes it possible for the unlifting function to be called
346− -- in threads distinct from its creator. See 'Persistence' and 'Limit'
347− -- settings for more information.
348− deriving (Eq, Ord, Show)
349−
350−-- | Persistence setting for the 'ConcUnlift' strategy.
351−--
352−-- Different functions require different persistence strategies. Examples:
353−--
354−-- - Lifting 'pooledMapConcurrentlyN' from the @unliftio@ library requires the
355−-- 'Ephemeral' strategy as we don't want jobs to share environment changes
356−-- made by previous jobs run in the same worker thread.
357−--
358−-- - Lifting 'Control.Concurrent.forkIOWithUnmask' requires the 'Persistent'
359−-- strategy, otherwise the unmasking function would start with a fresh
360−-- environment each time it's called.
361−data Persistence
362− = Ephemeral
363− -- ^ Don't persist the environment between calls to the unlifting function in
364− -- threads distinct from its creator.
365− | Persistent
366− -- ^ Persist the environment between calls to the unlifting function within a
367− -- particular thread.
368− deriving (Eq, Ord, Show)
369−
370−-- | Limit setting for the 'ConcUnlift' strategy.
371−data Limit
372− = Limited !Int
373− -- ^ Behavior dependent on the 'Persistence' setting.
374− --
375− -- For 'Ephemeral', it limits the amount of uses of the unlifting function in
376− -- threads distinct from its creator to @N@. The unlifting function will
377− -- create @N@ copies of the environment when called @N@ times and @K+1@ copies
378− -- when called @K < N@ times.
379− --
380− -- For 'Persistent', it limits the amount of threads, distinct from the
381− -- creator of the unlifting function, it can be called in to @N@. The amount
382− -- of calls to the unlifting function within a particular threads is
383− -- unlimited. The unlifting function will create @N@ copies of the environment
384− -- when called in @N@ threads and @K+1@ copies when called in @K < N@ threads.
385− | Unlimited
386− -- ^ Unlimited use of the unlifting function.
387− deriving (Eq, Ord, Show)
306+-- Dynamic dispatch
388307
389−-- | Get the current 'UnliftStrategy'.
390−unliftStrategy :: IOE :> es => Eff es UnliftStrategy
391−unliftStrategy = do
392− IdE (IOE unlift) <- getEffect
393− pure unlift
308+type role LocalEnv nominal nominal
394309
395−-- | Locally override the 'UnliftStrategy' with the given value.
310+-- | Opaque representation of the 'Eff' environment at the point of calling the
311+-- 'send' function, i.e. right before the control is passed to the effect
312+-- handler.
396313--
397−-- /Note:/ the strategy is reset to 'SeqUnlift' for new threads.
398−withUnliftStrategy :: IOE :> es => UnliftStrategy -> Eff es a -> Eff es a
399−withUnliftStrategy unlift = localEffect $ \_ -> IdE (IOE unlift)
314+-- The second type variable represents effects of a handler and is needed for
315+-- technical reasons to guarantee soundness.
316+newtype LocalEnv (localEs :: [Effect]) (handlerEs :: [Effect]) = LocalEnv (Env localEs)
317+
318+-- | Type signature of the effect handler.
319+type EffectHandler e es
320+ = forall a localEs. HasCallStack
321+ => LocalEnv localEs es
322+ -- ^ Capture of the local environment for handling local 'Eff' computations
323+ -- when @e@ is a higher order effect.
324+ -> e (Eff localEs) a
325+ -- ^ The effect performed in the local environment.
326+ -> Eff es a
400327
401−-- | Create an unlifting function with the current 'UnliftStrategy'.
328+-- | An adapter for dynamically dispatched effects.
402329--
403−-- This function is equivalent to 'withRunInIO', but has a 'HasCallStack'
404−-- constraint for accurate stack traces in case an insufficiently powerful
405−-- 'UnliftStrategy' is used and the unlifting function fails.
406−withEffToIO
407− :: (HasCallStack, IOE :> es)
408− => ((forall r. Eff es r -> IO r) -> IO a)
409− -- ^ Continuation with the unlifting function in scope.
410− -> Eff es a
411−withEffToIO f = unliftStrategy >>= \case
412− SeqUnlift -> unsafeEff $ \es -> seqUnliftEff es f
413− ConcUnlift p b -> withUnliftStrategy SeqUnlift $ do
414− unsafeEff $ \es -> concUnliftEff es p b f
330+-- Represents the effect handler bundled with its environment.
331+data HandlerA :: Effect -> Type where
332+ HandlerA :: !(Env es) -> !(EffectHandler e es) -> HandlerA e
333+
334+-- | Run a dynamically dispatched effect with the given handler.
335+runHandler :: HandlerA e -> Eff (e : es) a -> Eff es a
336+runHandler e m = unsafeEff $ \es0 -> do
337+ size0 <- sizeEnv es0
338+ E.bracket (unsafeConsEnv e relinker es0)
339+ (unsafeTailEnv size0)
340+ (\es -> unEff m es)
341+ where
342+ relinker :: Relinker HandlerA e
343+ relinker = Relinker $ \relink (HandlerA handlerEs handle) -> do
344+ newHandlerEs <- relink handlerEs
345+ pure $ HandlerA newHandlerEs handle
346+
347+-- | Send an operation of the given effect to its handler for execution.
348+send :: (HasCallStack, e :> es) => e (Eff es) a -> Eff es a
349+send op = unsafeEff $ \es -> do
350+ HandlerA handlerEs handle <- getEnv es
351+ unEff (handle (LocalEnv es) op) handlerEs
415352
416353----------------------------------------
417−-- Helpers
354+-- Static dispatch
418355
419−runEffect :: handler e -> Eff (e : es) a -> Eff es (a, handler e)
420−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
421367 size0 <- sizeEnv es0
422− bracket (unsafeConsEnv e0 noRelinker es0)
423− (unsafeTailEnv size0)
424− (\es -> (,) <$> unEff m es <*> getEnv es)
425−
426−evalEffect :: handler e -> Eff (e : es) a -> Eff es a
427−evalEffect e m = unsafeEff $ \es0 -> do
368+ E.bracket (unsafeConsEnv e0 noRelinker es0)
369+ (unsafeTailEnv size0)
370+ (\es -> (,) <$> unEff m es <*> getEnv es)
371+
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
428376 size0 <- sizeEnv es0
429− bracket (unsafeConsEnv e noRelinker es0)
430− (unsafeTailEnv size0)
431− (\es -> unEff m es)
432−
433−execEffect :: handler e -> Eff (e : es) a -> Eff es (handler e)
434−execEffect e0 m = unsafeEff $ \es0 -> do
377+ E.bracket (unsafeConsEnv e noRelinker es0)
378+ (unsafeTailEnv size0)
379+ (\es -> unEff m es)
380+
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
435385 size0 <- sizeEnv es0
436− bracket (unsafeConsEnv e0 noRelinker es0)
437− (unsafeTailEnv size0)
438− (\es -> unEff m es *> getEnv es)
439−
440−getEffect :: e :> es => Eff es (handler e)
441−getEffect = unsafeEff $ \es -> getEnv es
442−
443−putEffect :: e :> es => handler e -> Eff es ()
444−putEffect e = unsafeEff $ \es -> putEnv es e
445−
446−stateEffect :: e :> es => (handler e -> (a, handler e)) -> Eff es a
447−stateEffect f = unsafeEff $ \es -> stateEnv es f
448−
449−stateEffectM :: e :> es => (handler e -> Eff es (a, handler e)) -> Eff es a
450−stateEffectM f = unsafeEff $ \es -> mask $ \release -> do
386+ E.bracket (unsafeConsEnv e0 noRelinker es0)
387+ (unsafeTailEnv size0)
388+ (\es -> unEff m es *> getEnv es)
389+
390+-- | Fetch the current state of the effect.
391+getData :: e :> es => Eff es (DataA e)
392+getData = unsafeEff $ \es -> getEnv es
393+
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
397+
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
401+
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
451406 (a, e) <- (\e -> release $ unEff (f e) es) =<< getEnv es
452407 putEnv es e
453408 pure a
454409
455−localEffect :: e :> es => (handler e -> handler e) -> Eff es a -> Eff es a
456−localEffect f m = unsafeEff $ \es -> do
457− bracket (stateEnv es $ \e -> (e, f e))
458− (\e -> putEnv es e)
459− (\_ -> unEff m es)
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
413+ E.bracket (stateEnv es $ \e -> (e, f e))
414+ (\e -> putEnv es e)
415+ (\_ -> unEff m es)