Simplified eliminators #207
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robrix
changed the base branch from
separate-carrier-and-effect-modules
to
master
src/Control/Carrier/Choose/Church.hs
Outdated
| @@ -25,6 +26,9 @@ import Prelude hiding (fail) | |||
| runChoose :: (m b -> m b -> m b) -> (a -> m b) -> ChooseC m a -> m b | |||
| runChoose fork leaf m = runChooseC m fork leaf | |||
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| runChooseS :: (Applicative m, Semigroup b) => (a -> m b) -> ChooseC m a -> m b | |||
| runChooseS leaf = runChoose (liftA2 (<>)) leaf | |||
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We could supply runChooseA, but:
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You’d be giving up the assurance that you’ll have a non-empty container of results.
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You can always use
runChoose (liftA2 (<|>)) (pure . pure)orrunChooseS Alt >=> getAltif you must.
By contrast, there’s no reason to supply runChooseM as every Monoid is already a Semigroup.
| runCull (CullC m) = runNonDetC (runReader False m) (<|>) pure empty | ||
| -- prop> run (runCull (liftA2 (<|>)) (pure . pure) (pure empty) (pure a <|> pure b)) === [a, b] | ||
| runCull :: (m b -> m b -> m b) -> (a -> m b) -> m b -> CullC m a -> m b | ||
| runCull fork leaf nil = runNonDet fork leaf nil . runReader False . runCullC |
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This is much more flexible than the previous handlers employed (which required the use of another carrier for nondeterminism).
We no longer provide a handler interpreting into an underlying Alternative instance; instead, runCull (<|>) pure empty can be used, if one absolutely must.
| @@ -58,7 +66,7 @@ instance Alternative (NonDetC m) where | |||
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| instance Monad (NonDetC m) where | |||
| NonDetC a >>= f = NonDetC $ \ fork leaf nil -> | |||
| a fork (\ a' -> runNonDetC (f a') fork leaf nil) nil | |||
| a fork (runNonDet fork leaf nil . f) nil | |||
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This was by no means the point of this PR, but it’s certainly a nice side benefit that we can use the eliminators point-free.
| @@ -5,7 +5,7 @@ module Control.Carrier.Trace.Returning | |||
| -- * Trace carrier | |||
| , runTrace | |||
| , TraceC(..) | |||
| -- * Re-exports | |||
| @@ -36,5 +36,4 @@ cull m = send (Cull m pure) | |||
| -- >>> import Test.QuickCheck | |||
| -- >>> import Control.Carrier.Cull.Church | |||
| -- >>> import Control.Carrier.NonDet.Church | |||
| -- >>> import Control.Carrier.Pure | |||
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This is re-exported by Control.Carrier, and I missed cleaning these up.
| - The primary handlers (`runChoose`, `runNonDet`, `runCut`, `runCull`) take multiple continuations. | ||
| - Handlers which return an `Alternative` are suffixed with `A`, e.g. `runNonDetA`. | ||
| - Handlers which return a `Monoid` are suffixed with `M`, e.g. `runNonDetM`. | ||
| - Handlers which return a `Semigroup` are suffixed with `S`, e.g. `runChooseS`. |
| import Prelude hiding (fail) | ||
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| runChoose :: (m b -> m b -> m b) -> (a -> m b) -> ChooseC m a -> m b | ||
| runChoose fork leaf m = runChooseC m fork leaf | ||
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| runChooseS :: (Applicative m, S.Semigroup b) => (a -> m b) -> ChooseC m a -> m b |
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Can we get documentation for this, mentioning that it uses <> to merge its results?
| mfix (runChoose (liftA2 Fork) (pure . Leaf) | ||
| mfix (runChoose | ||
| (liftA2 Fork) | ||
| (pure . Leaf) | ||
| . f . fromJust . fold (Alt.<|>) Just) |
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Can we use something more descriptive than fromJust here? fromMaybe (“error: ChooseC mfix returned Just”)?
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This is being replaced in #233 anyway, so I’mma leave it as-is.
This PR simplifies the
NonDetChandler, and adds a couple of extra ones.