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add GEq instnaces for IORef and STRef #34

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add GEq instnaces for IORef and STRef #34

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1 change: 1 addition & 0 deletions some.cabal
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,7 @@ library
exposed-modules:
Data.GADT.Compare
Data.GADT.DeepSeq
Data.GADT.Instances
Data.GADT.Show
Data.Some
Data.Some.Church
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21 changes: 21 additions & 0 deletions src/Data/GADT/Instances.hs
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@@ -0,0 +1,21 @@
{-# LANGUAGE CPP #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}

module Data.GADT.Instances where

import Data.IORef (IORef)
import Data.STRef (STRef)
import Unsafe.Coerce (unsafeCoerce)

import Data.GADT.Compare (GEq(..))

#if __GLASGOW_HASKELL__ >=708
import Data.Typeable ((:~:)( Refl ))
#endif

instance GEq IORef where
a `geq` b = if a == unsafeCoerce b then Just $ unsafeCoerce Refl else Nothing

instance GEq (STRef s) where
a `geq` b = if a == unsafeCoerce b then Just $ unsafeCoerce Refl else Nothing