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Add PEq instances of composite functors from transformers package #4

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Add PEq instances of composite functors from transformers package #4

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add instance (PEq a, PEq b) => PEq (Product a b)
strake Mar 19, 2015
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add instance (PEq a, PEq b) => PEq (Sum a b)
strake Mar 19, 2015
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10 changes: 10 additions & 0 deletions src/Data/Comp/Param/Multi/Equality.hs
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Expand Up @@ -24,12 +24,22 @@ import Data.Comp.Param.Multi.Sum
import Data.Comp.Param.Multi.Ops
import Data.Comp.Param.Multi.HDifunctor
import Data.Comp.Param.Multi.FreshM
import Data.Functor.Product
import Data.Functor.Sum
import Control.Applicative

-- |Equality on parametric values. The equality test is performed inside the
-- 'FreshM' monad for generating fresh identifiers.
class PEq a where
peq :: a i -> a j -> FreshM Bool

instance (PEq a, PEq b) => PEq (Product a b) where peq (Pair u x) (Pair v y) = liftA2 (&&) (peq u v) (peq x y)

instance (PEq a, PEq b) => PEq (Sum a b) where
peq (InL x) (InL y) = peq x y
peq (InR x) (InR y) = peq x y
peq _ _ = pure False

instance Eq a => PEq (K a) where
peq (K x) (K y) = return $ x == y

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