Separate carrier and effect modules #204
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| {-# LANGUAGE FunctionalDependencies #-} | |||
| module Control.Carrier.Class | |||
| ( Carrier(..) | |||
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Instead of exporting run, Member, &c. from this module, we export them from Control.Carrier. Likewise, send has been moved into Control.Effect.Sum.
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| {-# LANGUAGE DeriveTraversable, FlexibleInstances, MultiParamTypeClasses, RankNTypes, TypeOperators, UndecidableInstances #-} | |||
| module Control.Carrier.Choose.Church | |||
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Carrier modules are now named descriptively of the implementation; .Church here indicates that this is a church-encoded carrier for Choose.
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| {-# LANGUAGE DeriveFunctor, FlexibleInstances, MultiParamTypeClasses, TypeOperators, UndecidableInstances #-} | |||
| module Control.Carrier.Empty.Maybe | |||
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Likewise with direct-stye carriers (i.e. those returning m (f a) for some functor f), we name the module after the functor being returned.
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| {-# LANGUAGE FlexibleInstances, GeneralizedNewtypeDeriving, MultiParamTypeClasses, TypeOperators, UndecidableInstances #-} | |||
| module Control.Carrier.Fresh.Strict | |||
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With stateful carriers, we instead note .Lazy or .Strict. (We only provide .Strict for the Fresh and Writer effects, but State offers both varieties.)
| import Control.Effect.Carrier | ||
| import Control.Effect.State | ||
| import Control.Carrier | ||
| import Control.Carrier.State.Strict |
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This illustrates the benefit of the new hierarchy nicely: the properties of the selected carrier are described by the module being imported.
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| instance (Carrier sig m, Member Choose sig) => S.Semigroup (Choosing m a) where |
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Kinda snuck this in here, but it’s extremely convenient to have available. We’re using an explicit qualified Data.Semigroup as S import here to accommodate ghc 8.2.
| -- | Conditional failure, returning only if the condition is 'True'. | ||
| guard :: (Carrier sig m, Member Empty sig) => Bool -> m () | ||
| guard True = pure () | ||
| guard False = empty |
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Snuck this in as well, with essentially the same rationale as above.
| instance MonadPlus (NonDetC m) | ||
| -- | Map a 'Foldable' collection of values into a nondeterministic computation using the supplied action. | ||
| foldMapA :: (Foldable t, Alternative m) => (a -> m b) -> t a -> m b | ||
| foldMapA f = getAlt #. foldMap (Alt #. f) |
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Snuck this in too. I end up defining this in just about every project that I use Alternative in; I’m considering proposing its addition to base (tho prolly under a different name, maybe asumMap because concat : concatMap :: asum : asumMap).
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| -- cf https://github.com/fused-effects/diffused-effects/pull/1#discussion_r323560758 | ||
| (#.) :: Coercible b c => (b -> c) -> (a -> b) -> (a -> c) | ||
| (#.) _ = coerce |
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🎩 @patrickt for pointing this out
| -- | Construct a request for an effect to be interpreted by some handler later on. | ||
| send :: (Member effect sig, Carrier sig m) => effect m a -> m a | ||
| send = eff . inj | ||
| {-# INLINE send #-} |
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Glad to have this, and the HFunctor/Effect instances, back where they belong.
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This PR separates carriers and effects into disjoint hierarchies. Goals include:
Control.Effect.*, implementations inControl.Carrier.*.base&transformers. (cf Define (terminal) Carrier instances for common monads? #183) I intend to explore this in separate PRs.StateC” instead of “whichever one the effect module re-exports.”Carriermachinery.On the other hand, this is also quite a disruptive PR, since it means pretty significant changes for consumers of the library. I’d therefore like to get input from users on this!
It also builds on several other PRs currently slated for 0.6:
AddWe’ll do this if we ship this as 0.6, but we might just ship it + some other stuff as 1.0; so will tackle that separately.Control.Effect.Carrierback in with a deprecation notice.Control.Effect.NonDetback in, re-exportingChoose&Empty.