10 lines
274 B
Haskell
10 lines
274 B
Haskell
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{-# LANGUAGE DerivingVia #-}
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module Trace where
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import Data.Functor.Contravariant (Op(..), Contravariant)
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import Data.Monoid (Ap(..))
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newtype Trace m a = Trace { trace :: a -> m () }
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deriving Contravariant via Op (m ())
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deriving (Semigroup, Monoid) via Op (Ap m ()) a
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