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Made writer work with arbitrary Monoids, not just lists

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ElvishJerricco 2016-03-02 05:51:23 -05:00
parent 86a8212cd8
commit 0846542b7d
1 changed files with 3 additions and 3 deletions
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6
src/Control/Monad/Freer/Writer.hs
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@ -35,6 +35,6 @@ tell :: Member (Writer o) r => o -> Eff r ()
tell o = send $ Writer o tell o = send $ Writer o
-- | Simple handler for Writer effects -- | Simple handler for Writer effects
runWriter :: Eff (Writer o ': r) a -> Eff r (a,[o]) runWriter :: Monoid o => Eff (Writer o ': r) a -> Eff r (a,o)
runWriter = handleRelay (\x -> return (x,[])) runWriter = handleRelay (\x -> return (x,mempty))
(\ (Writer o) k -> k () >>= \ (x,l) -> return (x,o:l)) (\ (Writer o) k -> k () >>= \ (x,l) -> return (x,o `mappend` l))