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{-# LANGUAGE MagicHash #-}
{-# LANGUAGE UnboxedTuples #-}
module T21239 where
import GHC.Exts
-- This test goes wrong if we don't properly decompose
-- when unifying ConcreteTv metavariables.
atomicModifyMutVar#
:: MutVar# s a
-> (a -> b)
-> State# s
-> (# State# s, c #)
atomicModifyMutVar# mv f s =
case unsafeCoerce# (atomicModifyMutVar2# mv f s) of
(# s', _, ~(_, res) #) -> (# s', res #)
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