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Uses generic derivation for reinterpret log example #178

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Jun 13, 2019
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Uses generic derivation for reinterpret log example #178

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19 changes: 2 additions & 17 deletions examples/ReinterpretLog.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
-- structured log messages as strings.


{-# LANGUAGE DeriveAnyClass #-}
{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE FlexibleContexts #-}
Expand Down Expand Up @@ -107,23 +108,7 @@ runApplication =
data Log (a :: Type) (m :: Type -> Type) (k :: Type)
= Log a k
deriving stock (Functor)

-- Log is a "first order" effect, so the Effect and HFunctor instance are
-- boilerplate. See https://github.com/fused-effects/fused-effects/issues/54
instance Effect (Log a) where
handle ::
Functor f
=> f ()
-> (forall x. f (m x) -> n (f x))
-> Log a m (m b)
-> Log a n (n (f b))
handle state handler =
coerce . fmap (handler . ((<$ state)))

instance HFunctor (Log a) where
hmap :: (forall x. m x -> n x) -> Log a m k -> Log a n k
hmap _ =
coerce
deriving anyclass (HFunctor, Effect)

-- Log an 'a'.
log ::
Expand Down