testsuite/tests/deriving/should_fail/T3833.hs


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{-# LANGUAGE Haskell2010 #-}

{-# LANGUAGE StandaloneDeriving #-}
-- {-# LANGUAGE GeneralizedNewtypeDeriving #-}

import Data.Monoid

newtype DecodeMap e = DecodeMap [e]

deriving instance Monoid (DecodeMap e)