polysemy-1.3.0.0: src/Polysemy/Internal/Combinators.hs
{-# LANGUAGE AllowAmbiguousTypes #-}
{-# OPTIONS_HADDOCK not-home #-}
module Polysemy.Internal.Combinators
( -- * First order
interpret
, intercept
, reinterpret
, reinterpret2
, reinterpret3
, rewrite
, transform
-- * Higher order
, interpretH
, interceptH
, reinterpretH
, reinterpret2H
, reinterpret3H
-- * Conditional
, interceptUsing
, interceptUsingH
-- * Statefulness
, stateful
, lazilyStateful
) where
import Control.Monad
import qualified Control.Monad.Trans.State.Lazy as LS
import qualified Control.Monad.Trans.State.Strict as S
import qualified Data.Tuple as S (swap)
import Polysemy.Internal
import Polysemy.Internal.CustomErrors
import Polysemy.Internal.Tactics
import Polysemy.Internal.Union
------------------------------------------------------------------------------
-- | A lazier version of 'Data.Tuple.swap'.
swap :: (a, b) -> (b, a)
swap ~(a, b) = (b, a)
firstOrder
:: ((forall m x. e m x -> Tactical e m r x) -> t)
-> (forall m x. e m x -> Sem r x)
-> t
firstOrder higher f = higher $ \(e :: e m x) -> liftT @m $ f e
{-# INLINE firstOrder #-}
------------------------------------------------------------------------------
-- | The simplest way to produce an effect handler. Interprets an effect @e@ by
-- transforming it into other effects inside of @r@.
interpret
:: FirstOrder e "interpret"
=> (∀ x m. e m x -> Sem r x)
-- ^ A natural transformation from the handled effect to other effects
-- already in 'Sem'.
-> Sem (e ': r) a
-> Sem r a
-- TODO(sandy): could probably give a `coerce` impl for `runTactics` here
interpret = firstOrder interpretH
{-# INLINE interpret #-}
------------------------------------------------------------------------------
-- | Like 'interpret', but for higher-order effects (ie. those which make use of
-- the @m@ parameter.)
--
-- See the notes on 'Tactical' for how to use this function.
interpretH
:: (∀ x m . e m x -> Tactical e m r x)
-- ^ A natural transformation from the handled effect to other effects
-- already in 'Sem'.
-> Sem (e ': r) a
-> Sem r a
interpretH f (Sem m) = m $ \u ->
case decomp u of
Left x -> liftSem $ hoist (interpretH f) x
Right (Weaving e s d y v) -> do
a <- runTactics s d v $ f e
pure $ y a
{-# INLINE interpretH #-}
------------------------------------------------------------------------------
-- | A highly-performant combinator for interpreting an effect statefully. See
-- 'stateful' for a more user-friendly variety of this function.
interpretInStateT
:: (∀ x m. e m x -> S.StateT s (Sem r) x)
-> s
-> Sem (e ': r) a
-> Sem r (s, a)
interpretInStateT f s (Sem m) = Sem $ \k ->
(S.swap <$!>) $ flip S.runStateT s $ m $ \u ->
case decomp u of
Left x -> S.StateT $ \s' ->
(S.swap <$!>)
. k
. weave (s', ())
(uncurry $ interpretInStateT f)
(Just . snd)
$ x
Right (Weaving e z _ y _) ->
fmap (y . (<$ z)) $ S.mapStateT (usingSem k) $ f e
{-# INLINE interpretInStateT #-}
------------------------------------------------------------------------------
-- | A highly-performant combinator for interpreting an effect statefully. See
-- 'stateful' for a more user-friendly variety of this function.
interpretInLazyStateT
:: (∀ x m. e m x -> LS.StateT s (Sem r) x)
-> s
-> Sem (e ': r) a
-> Sem r (s, a)
interpretInLazyStateT f s (Sem m) = Sem $ \k ->
fmap swap $ flip LS.runStateT s $ m $ \u ->
case decomp u of
Left x -> LS.StateT $ \s' ->
k . fmap swap
. weave (s', ())
(uncurry $ interpretInLazyStateT f)
(Just . snd)
$ x
Right (Weaving e z _ y _) ->
fmap (y . (<$ z)) $ LS.mapStateT (usingSem k) $ f e
{-# INLINE interpretInLazyStateT #-}
------------------------------------------------------------------------------
-- | Like 'interpret', but with access to an intermediate state @s@.
stateful
:: (∀ x m. e m x -> s -> Sem r (s, x))
-> s
-> Sem (e ': r) a
-> Sem r (s, a)
stateful f = interpretInStateT $ \e -> S.StateT $ (S.swap <$!>) . f e
{-# INLINE[3] stateful #-}
------------------------------------------------------------------------------
-- | Like 'interpret', but with access to an intermediate state @s@.
lazilyStateful
:: (∀ x m. e m x -> s -> Sem r (s, x))
-> s
-> Sem (e ': r) a
-> Sem r (s, a)
lazilyStateful f = interpretInLazyStateT $ \e -> LS.StateT $ fmap swap . f e
{-# INLINE[3] lazilyStateful #-}
------------------------------------------------------------------------------
-- | Like 'reinterpret', but for higher-order effects.
--
-- See the notes on 'Tactical' for how to use this function.
reinterpretH
:: forall e1 e2 r a
. (∀ m x. e1 m x -> Tactical e1 m (e2 ': r) x)
-- ^ A natural transformation from the handled effect to the new effect.
-> Sem (e1 ': r) a
-> Sem (e2 ': r) a
reinterpretH f (Sem m) = Sem $ \k -> m $ \u ->
case decompCoerce u of
Left x -> k $ hoist (reinterpretH f) $ x
Right (Weaving e s d y v) -> do
a <- usingSem k $ runTactics s (raiseUnder . d) v $ f e
pure $ y a
{-# INLINE[3] reinterpretH #-}
-- TODO(sandy): Make this fuse in with 'stateful' directly.
------------------------------------------------------------------------------
-- | Like 'interpret', but instead of removing the effect @e@, reencodes it in
-- some new effect @f@. This function will fuse when followed by
-- 'Polysemy.State.runState', meaning it's free to 'reinterpret' in terms of
-- the 'Polysemy.State.State' effect and immediately run it.
reinterpret
:: forall e1 e2 r a
. FirstOrder e1 "reinterpret"
=> (∀ m x. e1 m x -> Sem (e2 ': r) x)
-- ^ A natural transformation from the handled effect to the new effect.
-> Sem (e1 ': r) a
-> Sem (e2 ': r) a
reinterpret = firstOrder reinterpretH
{-# INLINE[3] reinterpret #-}
-- TODO(sandy): Make this fuse in with 'stateful' directly.
------------------------------------------------------------------------------
-- | Like 'reinterpret2', but for higher-order effects.
--
-- See the notes on 'Tactical' for how to use this function.
reinterpret2H
:: forall e1 e2 e3 r a
. (∀ m x. e1 m x -> Tactical e1 m (e2 ': e3 ': r) x)
-- ^ A natural transformation from the handled effect to the new effects.
-> Sem (e1 ': r) a
-> Sem (e2 ': e3 ': r) a
reinterpret2H f (Sem m) = Sem $ \k -> m $ \u ->
case decompCoerce u of
Left x -> k $ weaken $ hoist (reinterpret2H f) $ x
Right (Weaving e s d y v) -> do
a <- usingSem k $ runTactics s (raiseUnder2 . d) v $ f e
pure $ y a
{-# INLINE[3] reinterpret2H #-}
------------------------------------------------------------------------------
-- | Like 'reinterpret', but introduces /two/ intermediary effects.
reinterpret2
:: forall e1 e2 e3 r a
. FirstOrder e1 "reinterpret2"
=> (∀ m x. e1 m x -> Sem (e2 ': e3 ': r) x)
-- ^ A natural transformation from the handled effect to the new effects.
-> Sem (e1 ': r) a
-> Sem (e2 ': e3 ': r) a
reinterpret2 = firstOrder reinterpret2H
{-# INLINE[3] reinterpret2 #-}
------------------------------------------------------------------------------
-- | Like 'reinterpret3', but for higher-order effects.
--
-- See the notes on 'Tactical' for how to use this function.
reinterpret3H
:: forall e1 e2 e3 e4 r a
. (∀ m x. e1 m x -> Tactical e1 m (e2 ': e3 ': e4 ': r) x)
-- ^ A natural transformation from the handled effect to the new effects.
-> Sem (e1 ': r) a
-> Sem (e2 ': e3 ': e4 ': r) a
reinterpret3H f (Sem m) = Sem $ \k -> m $ \u ->
case decompCoerce u of
Left x -> k . weaken . weaken . hoist (reinterpret3H f) $ x
Right (Weaving e s d y v) -> do
a <- usingSem k $ runTactics s (raiseUnder3 . d) v $ f e
pure $ y a
{-# INLINE[3] reinterpret3H #-}
------------------------------------------------------------------------------
-- | Like 'reinterpret', but introduces /three/ intermediary effects.
reinterpret3
:: forall e1 e2 e3 e4 r a
. FirstOrder e1 "reinterpret3"
=> (∀ m x. e1 m x -> Sem (e2 ': e3 ': e4 ': r) x)
-- ^ A natural transformation from the handled effect to the new effects.
-> Sem (e1 ': r) a
-> Sem (e2 ': e3 ': e4 ': r) a
reinterpret3 = firstOrder reinterpret3H
{-# INLINE[3] reinterpret3 #-}
------------------------------------------------------------------------------
-- | Like 'interpret', but instead of handling the effect, allows responding to
-- the effect while leaving it unhandled. This allows you, for example, to
-- intercept other effects and insert logic around them.
intercept
:: ( Member e r
, FirstOrder e "intercept"
)
=> (∀ x m. e m x -> Sem r x)
-- ^ A natural transformation from the handled effect to other effects
-- already in 'Sem'.
-> Sem r a
-- ^ Unlike 'interpret', 'intercept' does not consume any effects.
-> Sem r a
intercept f = interceptH $ \(e :: e m x) -> liftT @m $ f e
{-# INLINE intercept #-}
------------------------------------------------------------------------------
-- | Like 'interceptH', but for higher-order effects.
--
-- See the notes on 'Tactical' for how to use this function.
interceptH
:: Member e r
=> (∀ x m. e m x -> Tactical e m r x)
-- ^ A natural transformation from the handled effect to other effects
-- already in 'Sem'.
-> Sem r a
-- ^ Unlike 'interpretH', 'interceptH' does not consume any effects.
-> Sem r a
interceptH = interceptUsingH membership
{-# INLINE interceptH #-}
------------------------------------------------------------------------------
-- | A variant of 'intercept' that accepts an explicit proof that the effect
-- is in the effect stack rather then requiring a 'Member' constraint.
--
-- This is useful in conjunction with 'Polysemy.Membership.tryMembership'
-- in order to conditionally perform 'intercept'.
--
-- @since 1.3.0.0
interceptUsing
:: FirstOrder e "interceptUsing"
=> ElemOf e r
-- ^ A proof that the handled effect exists in @r@.
-- This can be retrieved through 'Polysemy.Membership.membership' or
-- 'Polysemy.Membership.tryMembership'.
-> (∀ x m. e m x -> Sem r x)
-- ^ A natural transformation from the handled effect to other effects
-- already in 'Sem'.
-> Sem r a
-- ^ Unlike 'interpret', 'intercept' does not consume any effects.
-> Sem r a
interceptUsing pr f = interceptUsingH pr $ \(e :: e m x) -> liftT @m $ f e
{-# INLINE interceptUsing #-}
------------------------------------------------------------------------------
-- | A variant of 'interceptH' that accepts an explicit proof that the effect
-- is in the effect stack rather then requiring a 'Member' constraint.
--
-- This is useful in conjunction with 'Polysemy.Membership.tryMembership'
-- in order to conditionally perform 'interceptH'.
--
-- See the notes on 'Tactical' for how to use this function.
--
-- @since 1.3.0.0
interceptUsingH
:: ElemOf e r
-- ^ A proof that the handled effect exists in @r@.
-- This can be retrieved through 'Polysemy.Membership.membership' or
-- 'Polysemy.Membership.tryMembership'.
-> (∀ x m. e m x -> Tactical e m r x)
-- ^ A natural transformation from the handled effect to other effects
-- already in 'Sem'.
-> Sem r a
-- ^ Unlike 'interpretH', 'interceptUsingH' does not consume any effects.
-> Sem r a
interceptUsingH pr f (Sem m) = Sem $ \k -> m $ \u ->
case prjUsing pr u of
Just (Weaving e s d y v) ->
usingSem k $ fmap y $ runTactics s (raise . d) v $ f e
Nothing -> k $ hoist (interceptUsingH pr f) u
{-# INLINE interceptUsingH #-}
------------------------------------------------------------------------------
-- | Rewrite an effect @e1@ directly into @e2@, and put it on the top of the
-- effect stack.
--
-- @since 1.2.3.0
rewrite
:: forall e1 e2 r a
. (forall m x. e1 m x -> e2 m x)
-> Sem (e1 ': r) a
-> Sem (e2 ': r) a
rewrite f (Sem m) = Sem $ \k -> m $ \u ->
k $ hoist (rewrite f) $ case decompCoerce u of
Left x -> x
Right (Weaving e s d n y) -> Union Here $ Weaving (f e) s d n y
------------------------------------------------------------------------------
-- | Transform an effect @e1@ into an effect @e2@ that is already somewhere
-- inside of the stack.
--
-- @since 1.2.3.0
transform
:: forall e1 e2 r a
. Member e2 r
=> (forall m x. e1 m x -> e2 m x)
-> Sem (e1 ': r) a
-> Sem r a
transform f (Sem m) = Sem $ \k -> m $ \u ->
k $ hoist (transform f) $ case decomp u of
Left g -> g
Right (Weaving e s wv ex ins) -> injWeaving (Weaving (f e) s wv ex ins)