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add Semigroup and Monoid instances #98

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Apr 1, 2019
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add Semigroup and Monoid instances #98

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add Semigroup and Monoid instances
safareli Oct 4, 2018
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7 changes: 7 additions & 0 deletions src/Control/Monad/Free.purs
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Expand Up @@ -14,6 +14,7 @@ module Control.Monad.Free

import Prelude

import Control.Apply (lift2)
import Control.Monad.Rec.Class (class MonadRec, Step(..), tailRecM)
import Control.Monad.Trans.Class (class MonadTrans)

Expand Down Expand Up @@ -111,6 +112,12 @@ instance traversableFree :: Traversable f => Traversable (Free f) where
Right a -> pure <$> f a
sequence tma = traverse identity tma

instance semigroupFree :: Semigroup a => Semigroup (Free f a) where
append = lift2 append

instance monoidFree :: Monoid a => Monoid (Free f a) where
mempty = pure mempty

-- | Lift an impure value described by the generating type constructor `f` into
-- | the free monad.
liftF :: forall f. f ~> Free f
Expand Down