18 lines
473 B
Haskell
18 lines
473 B
Haskell
module XMonad.Configurable (Configurable, EndoM(..), configure) where
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import Control.Monad ((<=<))
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import Control.Monad.Reader
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newtype EndoM m a = EndoM { appEndoM :: a -> m a }
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instance Monad m => Semigroup (EndoM m a) where
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EndoM f <> EndoM g = EndoM (f <=< g)
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instance Monad m => Monoid (EndoM m a) where
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mempty = EndoM pure
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type Configurable a = EndoM (Reader a) a
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configure :: Configurable a -> a
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configure (EndoM f) = fix (\self -> runReader (f self) self)
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