@@ -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− ( -- * The 'Eff' monad
9+ ( -- * Monad
1010 Eff
1111 , runPureEff
1212
@@ -22,41 +22,47 @@ module Effectful.Internal.Monad
2222 , IOE
2323 , runEff
2424
25− -- * Prim
25+ -- * Primitive
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(..)
3637
37− -- ** Low-level unlifts
38+ --- *** Low-level helpers
3839 , seqUnliftIO
3940 , concUnliftIO
4041
4142 -- * Effects
4243
43− -- ** Dynamic dispatch
44+ -- ** Handler
4445 , EffectHandler
4546 , LocalEnv(..)
46− , HandlerA(..)
47+ , Handler(..)
4748 , runHandler
49+
50+ -- *** Sending operations
4851 , send
4952
50− -- ** Static dispatch
51− , DataA(..)
52− , runData
53− , evalData
54− , execData
55− , getData
56− , putData
57− , stateData
58− , stateDataM
59− , localData
53+ -- ** Primitive
54+
55+ -- *** Running
56+ , runEffect
57+ , evalEffect
58+ , execEffect
59+
60+ -- *** Modification
61+ , getEffect
62+ , putEffect
63+ , stateEffect
64+ , stateEffectM
65+ , localEffect
6066 ) where
6167
6268import Control.Applicative (liftA2)
@@ -79,43 +85,44 @@ import Effectful.Internal.Unlift
7985
8086type role Eff nominal representational
8187
82−-- | The 'Eff' monad provides the implementation of a computation that performs
88+-- | The 'Eff' monad provides the implementation of an operation that performs
8389-- an arbitrary set of effects. In @'Eff' es a@, @es@ is a type-level list that
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:
90+-- contains all the effects that the operation may perform. For example, an
91+-- operation that produces an 'Integer' by consuming a 'String' from the global
92+-- environment and acting upon a single mutable cell containing a 'Bool' would
93+-- have the following type:
8894--
8995-- @
90−-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.Local.State' 'Bool'] 'Integer'
96+-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.State' 'Bool'] 'Integer'
9197-- @
9298--
9399-- Normally, a concrete list of effects is not used to parameterize 'Eff'.
94100-- Instead, the '(:>)' type class is used to express constraints on the list of
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:
101+-- effects without coupling an operation to a concrete list of effects. For
102+-- example, the above example would more commonly be expressed with the
103+-- following type:
97104--
98105-- @
99−-- ('Effectful.Reader.Reader' 'String' ':>' es, 'Effectful.State.Local.State' 'Bool' ':>' es) => 'Eff' es 'Integer'
106+-- ('Effectful.Reader.Reader' 'String' ':>' es, 'Effectful.State.State' 'Bool' ':>' es) => 'Eff' es 'Integer'
100107-- @
101108--
102−-- This abstraction allows the computation to be used in functions that may
109+-- This abstraction allows the operation to be used in functions that may
103110-- perform other effects, and it also allows the effects to be handled in any
104111-- order.
105112newtype Eff (es :: [Effect]) a = Eff (Env es -> IO a)
106113 deriving (Monoid, Semigroup)
107114
108−-- | Run a pure 'Eff' computation.
115+-- | Run a pure 'Eff' operation.
109116--
110−-- For running computations with side effects see 'runEff'.
117+-- For running operations with side effects see 'runEff'.
111118runPureEff :: Eff '[] a -> a
112119runPureEff (Eff m) =
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).
120+ -- unsafePerformIO is safe here since IOE was not on the stack, so no IO with
121+ -- side effects was performed (unless someone sneakily introduced side effects
122+ -- with unsafeEff, but then all bets are off).
116123 --
117124 -- Moreover, internals don't allocate any resources that require explicit
118− -- cleanup actions to run.
125+ -- cleanup actions to run, so the "Dupable" part should also be just fine.
119126 unsafeDupablePerformIO $ m =<< emptyEnv
120127
121128----------------------------------------
@@ -128,14 +135,14 @@ unEff (Eff m) = m
128135-- | Access the underlying 'IO' monad along with the environment.
129136--
130137-- This function is __unsafe__ because it can be used to introduce arbitrary
131−-- 'IO' actions into pure 'Eff' computations.
138+-- 'IO' actions into pure 'Eff' operations.
132139unsafeEff :: (Env es -> IO a) -> Eff es a
133140unsafeEff m = Eff (oneShot m)
134141
135142-- | Access the underlying 'IO' monad.
136143--
137144-- This function is __unsafe__ because it can be used to introduce arbitrary
138−-- 'IO' actions into pure 'Eff' computations.
145+-- 'IO' actions into pure 'Eff' operations.
139146unsafeEff_ :: IO a -> Eff es a
140147unsafeEff_ m = unsafeEff $ \_ -> m
141148
@@ -145,12 +152,12 @@ unsafeEff_ m = unsafeEff $ \_ -> m
145152-- | Get the current 'UnliftStrategy'.
146153unliftStrategy :: IOE :> es => Eff es UnliftStrategy
147154unliftStrategy = do
148− DataA (IOE unlift) <- getData
155+ IdE (IOE unlift) <- getEffect
149156 pure unlift
150157
151158-- | Locally override the 'UnliftStrategy' with the given value.
152159withUnliftStrategy :: IOE :> es => UnliftStrategy -> Eff es a -> Eff es a
153−withUnliftStrategy unlift = localData $ \_ -> DataA (IOE unlift)
160+withUnliftStrategy unlift = localEffect $ \_ -> IdE (IOE unlift)
154161
155162-- | Create an unlifting function with the current 'UnliftStrategy'.
156163--
@@ -158,7 +165,7 @@ withUnliftStrategy unlift = localData $ \_ -> DataA (IOE unlift)
158165-- constraint for accurate stack traces in case an insufficiently powerful
159166-- 'UnliftStrategy' is used and the unlifting function fails.
160167--
161−-- /Note:/ the strategy is reset to 'SeqUnlift' inside the continuation.
168+-- /Note:/ the strategy is reset to 'SeqUnlift' for new threads.
162169withEffToIO
163170 :: (HasCallStack, IOE :> es)
164171 => ((forall r. Eff es r -> IO r) -> IO a)
@@ -169,25 +176,25 @@ withEffToIO f = unliftStrategy >>= \case
169176 ConcUnlift p b -> withUnliftStrategy SeqUnlift $ do
170177 unsafeEff $ \es -> concUnliftIO es p b f
171178
172−-- | Create an unlifting function with the 'SeqUnlift' strategy.
179+-- | Lower 'Eff' operations into 'IO' ('SeqUnlift').
180+--
181+-- Exceptions thrown by this function:
182+--
183+-- - 'InvalidUseOfSeqUnlift' if the unlift function is used in another thread.
173184seqUnliftIO
174185 :: HasCallStack
175186 => Env es
176− -- ^ The environment.
177187 -> ((forall r. Eff es r -> IO r) -> IO a)
178− -- ^ Continuation with the unlifting function in scope.
179188 -> IO a
180189seqUnliftIO es k = seqUnlift k es unEff
181190
182−-- | Create an unlifting function with the 'ConcUnlift' strategy.
191+-- | Lower 'Eff' operations into 'IO' ('ConcUnlift').
183192concUnliftIO
184193 :: HasCallStack
185194 => Env es
186− -- ^ The environment.
187195 -> Persistence
188196 -> Limit
189197 -> ((forall r. Eff es r -> IO r) -> IO a)
190− -- ^ Continuation with the unlifting function in scope.
191198 -> IO a
192199concUnliftIO es persistence limit k = concUnlift persistence limit k es unEff
193200
@@ -258,15 +265,15 @@ instance Fail :> es => MonadFail (Eff es) where
258265----------------------------------------
259266-- IO
260267
261−-- | Run arbitrary 'IO' computations via 'MonadIO' or 'MonadUnliftIO'.
268+-- | Run arbitrary 'IO' operations via 'MonadIO' or 'MonadUnliftIO'.
262269newtype IOE :: Effect where
263270 IOE :: UnliftStrategy -> IOE m r
264271
265−-- | Run an 'Eff' computation with side effects.
272+-- | Run an 'Eff' operation with side effects.
266273--
267−-- For running pure computations see 'runPureEff'.
274+-- For running pure operations see 'runPureEff'.
268275runEff :: Eff '[IOE] a -> IO a
269−runEff m = unEff (evalData (DataA (IOE SeqUnlift)) m) =<< emptyEnv
276+runEff m = unEff (evalEffect (IdE (IOE SeqUnlift)) m) =<< emptyEnv
270277
271278instance IOE :> es => MonadIO (Eff es) where
272279 liftIO = unsafeEff_
@@ -290,20 +297,20 @@ instance IOE :> es => MonadBaseControl IO (Eff es) where
290297----------------------------------------
291298-- Primitive
292299
293−-- | Provide the ability to perform primitive state-transformer actions.
300+-- | An effect to perform primitive state-transformer actions.
294301data Prim :: Effect where
295302 Prim :: Prim m r
296303
297−-- | Run an 'Eff' computation with primitive state-transformer actions.
304+-- | Run an 'Eff' operation with primitive state-transformer actions.
298305runPrim :: IOE :> es => Eff (Prim : es) a -> Eff es a
299−runPrim = evalData (DataA Prim)
306+runPrim = evalEffect (IdE Prim)
300307
301308instance Prim :> es => PrimMonad (Eff es) where
302309 type PrimState (Eff es) = RealWorld
303310 primitive = unsafeEff_ . IO
304311
305312----------------------------------------
306−-- Dynamic dispatch
313+-- Handler
307314
308315type role LocalEnv nominal nominal
309316
@@ -319,97 +326,78 @@ newtype LocalEnv (localEs :: [Effect]) (handlerEs :: [Effect]) = LocalEnv (Env l
319326type EffectHandler e es
320327 = forall a localEs. HasCallStack
321328 => LocalEnv localEs es
322− -- ^ Capture of the local environment for handling local 'Eff' computations
323− -- when @e@ is a higher order effect.
329+ -- ^ Capture of the local environment for handling local 'Eff' operations when
330+ -- @e@ is a higher order effect.
324331 -> e (Eff localEs) a
325332 -- ^ The effect performed in the local environment.
326333 -> Eff es a
327334
328335-- | An adapter for dynamically dispatched effects.
329336--
330−-- Represents the effect handler bundled with its environment.
331−data HandlerA :: Effect -> Type where
332− HandlerA :: !(Env es) -> !(EffectHandler e es) -> HandlerA e
337+-- Represents the effect handler bundled along with its environment.
338+data Handler :: Effect -> Type where
339+ Handler :: !(Env es) -> !(EffectHandler e es) -> Handler e
333340
334−-- | Run a dynamically dispatched effect with the given handler.
335−runHandler :: HandlerA e -> Eff (e : es) a -> Eff es a
341+-- | Run the effect with the given handler.
342+runHandler :: Handler e -> Eff (e : es) a -> Eff es a
336343runHandler e m = unsafeEff $ \es0 -> do
337344 size0 <- sizeEnv es0
338345 E.bracket (unsafeConsEnv e relinker es0)
339346 (unsafeTailEnv size0)
340347 (\es -> unEff m es)
341348 where
342− relinker :: Relinker HandlerA e
343− relinker = Relinker $ \relink (HandlerA handlerEs handle) -> do
344− newHandlerEs <- relink handlerEs
345− pure $ HandlerA newHandlerEs handle
349+ relinker :: Relinker Handler e
350+ relinker = Relinker $ \relink (Handler env handle) -> do
351+ newEnv <- relink env
352+ pure $ Handler newEnv handle
346353
347354-- | Send an operation of the given effect to its handler for execution.
348355send :: (HasCallStack, e :> es) => e (Eff es) a -> Eff es a
349356send op = unsafeEff $ \es -> do
350− HandlerA handlerEs handle <- getEnv es
357+ Handler handlerEs handle <- getEnv es
351358 unEff (handle (LocalEnv es) op) handlerEs
352359
353360----------------------------------------
354−-- Static dispatch
361+-- Helpers
355362
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
363+runEffect :: adapter e -> Eff (e : es) a -> Eff es (a, adapter e)
364+runEffect e0 m = unsafeEff $ \es0 -> do
367365 size0 <- sizeEnv es0
368366 E.bracket (unsafeConsEnv e0 noRelinker es0)
369367 (unsafeTailEnv size0)
370368 (\es -> (,) <$> unEff m es <*> getEnv es)
371369
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
370+evalEffect :: adapter e -> Eff (e : es) a -> Eff es a
371+evalEffect e m = unsafeEff $ \es0 -> do
376372 size0 <- sizeEnv es0
377373 E.bracket (unsafeConsEnv e noRelinker es0)
378374 (unsafeTailEnv size0)
379375 (\es -> unEff m es)
380376
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
377+execEffect :: adapter e -> Eff (e : es) a -> Eff es (adapter e)
378+execEffect e0 m = unsafeEff $ \es0 -> do
385379 size0 <- sizeEnv es0
386380 E.bracket (unsafeConsEnv e0 noRelinker es0)
387381 (unsafeTailEnv size0)
388382 (\es -> unEff m es *> getEnv es)
389383
390−-- | Fetch the current state of the effect.
391−getData :: e :> es => Eff es (DataA e)
392−getData = unsafeEff $ \es -> getEnv es
384+getEffect :: e :> es => Eff es (adapter e)
385+getEffect = unsafeEff $ \es -> getEnv es
393386
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
387+putEffect :: e :> es => adapter e -> Eff es ()
388+putEffect e = unsafeEff $ \es -> putEnv es e
397389
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
390+stateEffect :: e :> es => (adapter e -> (a, adapter e)) -> Eff es a
391+stateEffect f = unsafeEff $ \es -> stateEnv es f
401392
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
393+stateEffectM :: e :> es => (adapter e -> Eff es (a, adapter e)) -> Eff es a
394+stateEffectM f = unsafeEff $ \es -> E.mask $ \release -> do
406395 (a, e) <- (\e -> release $ unEff (f e) es) =<< getEnv es
407396 putEnv es e
408397 pure a
409398
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
399+localEffect :: e :> es => (adapter e -> adapter e) -> Eff es a -> Eff es a
400+localEffect f m = unsafeEff $ \es -> do
413401 E.bracket (stateEnv es $ \e -> (e, f e))
414402 (\e -> putEnv es e)
415403 (\_ -> unEff m es)