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add extra instances for GEq and GCompare #31

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add extra instances for GEq and GCompare #31

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19 changes: 19 additions & 0 deletions src/Data/GADT/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@ import Data.Maybe (isJust, isNothing)
import Data.Monoid (Monoid (..))
import Data.Semigroup (Semigroup (..))
import Data.Type.Equality ((:~:) (..))
import GHC.Generics ((:+:) (..))

#if __GLASGOW_HASKELL__ >=708
import Data.Typeable (Typeable)
Expand Down Expand Up @@ -181,6 +182,15 @@ instance (GEq a, GEq b) => GEq (Product a b) where
Refl <- geq y y'
return Refl

instance (GEq f, GEq g) => GEq (f :+: g) where
geq x y = case x of
L1 f -> case y of
L1 f' -> geq f f'
R1 _ -> Nothing
R1 g -> case y of
L1 _ -> Nothing
R1 g' -> geq g g'

#if MIN_VERSION_base(4,10,0)
instance GEq TR.TypeRep where
geq = testEquality
Expand Down Expand Up @@ -297,6 +307,15 @@ instance (GCompare a, GCompare b) => GCompare (Product a b) where
GEQ -> GEQ
GGT -> GGT

instance (GCompare f, GCompare g) => GCompare (f :+: g) where
gcompare x y = case x of
L1 f -> case y of
L1 f' -> gcompare f f'
R1 _ -> GLT
R1 g -> case y of
L1 _ -> GLT
R1 g' -> gcompare g g'

-------------------------------------------------------------------------------
-- Some
-------------------------------------------------------------------------------
Expand Down