@@ -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 +22,49 @@ 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− , seqUnliftIO
39− , concUnliftIO
38+ --- *** Low-level helpers
39+ , unsafeLiftMapIO
40+ , unsafeUnliftIO
41+ , seqUnliftEff
42+ , concUnliftEff
4043
4144 -- * Effects
4245
43− -- ** Dynamic dispatch
46+ -- ** Handler
4447 , EffectHandler
4548 , LocalEnv(..)
46− , HandlerA(..)
49+ , Handler(..)
4750 , runHandler
51+
52+ -- *** Sending operations
4853 , send
4954
50− -- ** Static dispatch
51− , DataA(..)
52− , runData
53− , evalData
54− , execData
55− , getData
56− , putData
57− , stateData
58− , stateDataM
59− , localData
55+ -- ** Primitive
56+
57+ -- *** Running
58+ , runEffect
59+ , evalEffect
60+ , execEffect
61+
62+ -- *** Modification
63+ , getEffect
64+ , putEffect
65+ , stateEffect
66+ , stateEffectM
67+ , localEffect
6068 ) where
6169
6270import Control.Applicative (liftA2)
@@ -79,43 +87,44 @@ import Effectful.Internal.Unlift
7987
8088type role Eff nominal representational
8189
82−-- | The 'Eff' monad provides the implementation of a computation that performs
90+-- | The 'Eff' monad provides the implementation of an operation that performs
8391-- 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:
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:
8896--
8997-- @
90−-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.Local.State' 'Bool'] 'Integer'
98+-- 'Eff' '['Effectful.Reader.Reader' 'String', 'Effectful.State.State' 'Bool'] 'Integer'
9199-- @
92100--
93101-- Normally, a concrete list of effects is not used to parameterize 'Eff'.
94102-- 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:
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:
97106--
98107-- @
99−-- ('Effectful.Reader.Reader' 'String' ':>' es, 'Effectful.State.Local.State' 'Bool' ':>' es) => 'Eff' es 'Integer'
108+-- ('Effectful.Reader.Reader' 'String' ':>' es, 'Effectful.State.State' 'Bool' ':>' es) => 'Eff' es 'Integer'
100109-- @
101110--
102−-- This abstraction allows the computation to be used in functions that may
111+-- This abstraction allows the operation to be used in functions that may
103112-- perform other effects, and it also allows the effects to be handled in any
104113-- order.
105114newtype Eff (es :: [Effect]) a = Eff (Env es -> IO a)
106115 deriving (Monoid, Semigroup)
107116
108−-- | Run a pure 'Eff' computation.
117+-- | Run a pure 'Eff' operation.
109118--
110−-- For running computations with side effects see 'runEff'.
119+-- For running operations with side effects see 'runEff'.
111120runPureEff :: Eff '[] a -> a
112121runPureEff (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).
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).
116125 --
117126 -- Moreover, internals don't allocate any resources that require explicit
118− -- cleanup actions to run.
127+ -- cleanup actions to run, so the "Dupable" part should also be just fine.
119128 unsafeDupablePerformIO $ m =<< emptyEnv
120129
121130----------------------------------------
@@ -128,68 +137,101 @@ unEff (Eff m) = m
128137-- | Access the underlying 'IO' monad along with the environment.
129138--
130139-- This function is __unsafe__ because it can be used to introduce arbitrary
131−-- 'IO' actions into pure 'Eff' computations.
140+-- 'IO' actions into pure 'Eff' operations.
132141unsafeEff :: (Env es -> IO a) -> Eff es a
133142unsafeEff m = Eff (oneShot m)
134143
135144-- | Access the underlying 'IO' monad.
136145--
137146-- This function is __unsafe__ because it can be used to introduce arbitrary
138−-- 'IO' actions into pure 'Eff' computations.
147+-- 'IO' actions into pure 'Eff' operations.
139148unsafeEff_ :: IO a -> Eff es a
140149unsafeEff_ m = unsafeEff $ \_ -> m
141150
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+
142184----------------------------------------
143−-- Unlifting IO
185+-- Unlifting Eff
144186
145187-- | Get the current 'UnliftStrategy'.
146188unliftStrategy :: IOE :> es => Eff es UnliftStrategy
147189unliftStrategy = do
148− DataA (IOE unlift) <- getData
190+ IdE (IOE unlift) <- getEffect
149191 pure unlift
150192
151193-- | Locally override the 'UnliftStrategy' with the given value.
152194withUnliftStrategy :: IOE :> es => UnliftStrategy -> Eff es a -> Eff es a
153−withUnliftStrategy unlift = localData $ \_ -> DataA (IOE unlift)
195+withUnliftStrategy unlift = localEffect $ \_ -> IdE (IOE unlift)
154196
155−-- | Create an unlifting function with the current 'UnliftStrategy'.
197+-- | Lower 'Eff' operations into 'IO' ('SeqUnlift').
156198--
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.
199+-- Exceptions thrown by this function:
160200--
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
171−
172−-- | Create an unlifting function with the 'SeqUnlift' strategy.
173−seqUnliftIO
201+-- - 'InvalidUseOfSeqUnlift' if the unlift function is used in another thread.
202+seqUnliftEff
174203 :: HasCallStack
175204 => Env es
176− -- ^ The environment.
177205 -> ((forall r. Eff es r -> IO r) -> IO a)
178− -- ^ Continuation with the unlifting function in scope.
179206 -> IO a
180−seqUnliftIO es k = seqUnlift k es unEff
207+seqUnliftEff es k = seqUnliftIO k es unEff
181208
182−-- | Create an unlifting function with the 'ConcUnlift' strategy.
183−concUnliftIO
209+-- | Lower 'Eff' operations into 'IO' ('ConcUnlift').
210+concUnliftEff
184211 :: HasCallStack
185212 => Env es
186− -- ^ The environment.
187213 -> Persistence
188214 -> Limit
189215 -> ((forall r. Eff es r -> IO r) -> IO a)
190− -- ^ Continuation with the unlifting function in scope.
191216 -> IO a
192−concUnliftIO es persistence limit k = concUnlift persistence limit k es unEff
217+concUnliftEff es persistence limit k = concUnliftIO persistence limit k es unEff
218+
219+-- | Create an unlifting function with the current 'UnliftStrategy'.
220+--
221+-- This function is equivalent to 'withRunInIO', but has a 'HasCallStack'
222+-- constraint for accurate stack traces in case an insufficiently powerful
223+-- 'UnliftStrategy' is used and the unlifting function fails.
224+--
225+-- /Note:/ the strategy is reset to 'SeqUnlift' for new threads.
226+withEffToIO
227+ :: (HasCallStack, IOE :> es)
228+ => ((forall r. Eff es r -> IO r) -> IO a)
229+ -- ^ Continuation with the unlifting function in scope.
230+ -> Eff es a
231+withEffToIO f = unliftStrategy >>= \case
232+ SeqUnlift -> unsafeEff $ \es -> seqUnliftEff es f
233+ ConcUnlift p b -> withUnliftStrategy SeqUnlift $ do
234+ unsafeEff $ \es -> concUnliftEff es p b f
193235
194236----------------------------------------
195237-- Base
@@ -258,15 +300,15 @@ instance Fail :> es => MonadFail (Eff es) where
258300----------------------------------------
259301-- IO
260302
261−-- | Run arbitrary 'IO' computations via 'MonadIO' or 'MonadUnliftIO'.
303+-- | Run arbitrary 'IO' operations via 'MonadIO' or 'MonadUnliftIO'.
262304newtype IOE :: Effect where
263305 IOE :: UnliftStrategy -> IOE m r
264306
265−-- | Run an 'Eff' computation with side effects.
307+-- | Run an 'Eff' operation with side effects.
266308--
267−-- For running pure computations see 'runPureEff'.
309+-- For running pure operations see 'runPureEff'.
268310runEff :: Eff '[IOE] a -> IO a
269−runEff m = unEff (evalData (DataA (IOE SeqUnlift)) m) =<< emptyEnv
311+runEff m = unEff (evalEffect (IdE (IOE SeqUnlift)) m) =<< emptyEnv
270312
271313instance IOE :> es => MonadIO (Eff es) where
272314 liftIO = unsafeEff_
@@ -290,20 +332,20 @@ instance IOE :> es => MonadBaseControl IO (Eff es) where
290332----------------------------------------
291333-- Primitive
292334
293−-- | Provide the ability to perform primitive state-transformer actions.
335+-- | An effect to perform primitive state-transformer actions.
294336data Prim :: Effect where
295337 Prim :: Prim m r
296338
297−-- | Run an 'Eff' computation with primitive state-transformer actions.
339+-- | Run an 'Eff' operation with primitive state-transformer actions.
298340runPrim :: IOE :> es => Eff (Prim : es) a -> Eff es a
299−runPrim = evalData (DataA Prim)
341+runPrim = evalEffect (IdE Prim)
300342
301343instance Prim :> es => PrimMonad (Eff es) where
302344 type PrimState (Eff es) = RealWorld
303345 primitive = unsafeEff_ . IO
304346
305347----------------------------------------
306−-- Dynamic dispatch
348+-- Handler
307349
308350type role LocalEnv nominal nominal
309351
@@ -319,97 +361,78 @@ newtype LocalEnv (localEs :: [Effect]) (handlerEs :: [Effect]) = LocalEnv (Env l
319361type EffectHandler e es
320362 = forall a localEs. HasCallStack
321363 => LocalEnv localEs es
322− -- ^ Capture of the local environment for handling local 'Eff' computations
323− -- when @e@ is a higher order effect.
364+ -- ^ Capture of the local environment for handling local 'Eff' operations when
365+ -- @e@ is a higher order effect.
324366 -> e (Eff localEs) a
325367 -- ^ The effect performed in the local environment.
326368 -> Eff es a
327369
328370-- | An adapter for dynamically dispatched effects.
329371--
330−-- Represents the effect handler bundled with its environment.
331−data HandlerA :: Effect -> Type where
332− HandlerA :: !(Env es) -> !(EffectHandler e es) -> HandlerA e
372+-- Represents the effect handler bundled along with its environment.
373+data Handler :: Effect -> Type where
374+ Handler :: !(Env es) -> !(EffectHandler e es) -> Handler e
333375
334−-- | Run a dynamically dispatched effect with the given handler.
335−runHandler :: HandlerA e -> Eff (e : es) a -> Eff es a
376+-- | Run the effect with the given handler.
377+runHandler :: Handler e -> Eff (e : es) a -> Eff es a
336378runHandler e m = unsafeEff $ \es0 -> do
337379 size0 <- sizeEnv es0
338380 E.bracket (unsafeConsEnv e relinker es0)
339381 (unsafeTailEnv size0)
340382 (\es -> unEff m es)
341383 where
342− relinker :: Relinker HandlerA e
343− relinker = Relinker $ \relink (HandlerA handlerEs handle) -> do
344− newHandlerEs <- relink handlerEs
345− pure $ HandlerA newHandlerEs handle
384+ relinker :: Relinker Handler e
385+ relinker = Relinker $ \relink (Handler env handle) -> do
386+ newEnv <- relink env
387+ pure $ Handler newEnv handle
346388
347389-- | Send an operation of the given effect to its handler for execution.
348390send :: (HasCallStack, e :> es) => e (Eff es) a -> Eff es a
349391send op = unsafeEff $ \es -> do
350− HandlerA handlerEs handle <- getEnv es
392+ Handler handlerEs handle <- getEnv es
351393 unEff (handle (LocalEnv es) op) handlerEs
352394
353395----------------------------------------
354−-- Static dispatch
396+-- Helpers
355397
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
398+runEffect :: adapter e -> Eff (e : es) a -> Eff es (a, adapter e)
399+runEffect e0 m = unsafeEff $ \es0 -> do
367400 size0 <- sizeEnv es0
368401 E.bracket (unsafeConsEnv e0 noRelinker es0)
369402 (unsafeTailEnv size0)
370403 (\es -> (,) <$> unEff m es <*> getEnv es)
371404
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
405+evalEffect :: adapter e -> Eff (e : es) a -> Eff es a
406+evalEffect e m = unsafeEff $ \es0 -> do
376407 size0 <- sizeEnv es0
377408 E.bracket (unsafeConsEnv e noRelinker es0)
378409 (unsafeTailEnv size0)
379410 (\es -> unEff m es)
380411
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
412+execEffect :: adapter e -> Eff (e : es) a -> Eff es (adapter e)
413+execEffect e0 m = unsafeEff $ \es0 -> do
385414 size0 <- sizeEnv es0
386415 E.bracket (unsafeConsEnv e0 noRelinker es0)
387416 (unsafeTailEnv size0)
388417 (\es -> unEff m es *> getEnv es)
389418
390−-- | Fetch the current state of the effect.
391−getData :: e :> es => Eff es (DataA e)
392−getData = unsafeEff $ \es -> getEnv es
419+getEffect :: e :> es => Eff es (adapter e)
420+getEffect = unsafeEff $ \es -> getEnv es
393421
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
422+putEffect :: e :> es => adapter e -> Eff es ()
423+putEffect e = unsafeEff $ \es -> putEnv es e
397424
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
425+stateEffect :: e :> es => (adapter e -> (a, adapter e)) -> Eff es a
426+stateEffect f = unsafeEff $ \es -> stateEnv es f
401427
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
428+stateEffectM :: e :> es => (adapter e -> Eff es (a, adapter e)) -> Eff es a
429+stateEffectM f = unsafeEff $ \es -> E.mask $ \release -> do
406430 (a, e) <- (\e -> release $ unEff (f e) es) =<< getEnv es
407431 putEnv es e
408432 pure a
409433
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
434+localEffect :: e :> es => (adapter e -> adapter e) -> Eff es a -> Eff es a
435+localEffect f m = unsafeEff $ \es -> do
413436 E.bracket (stateEnv es $ \e -> (e, f e))
414437 (\e -> putEnv es e)
415438 (\_ -> unEff m es)