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{-|
Module : Utils.Monad
Copyright : (c) UU, 2019
License : MIT
Maintainer : Tom Smeding
Stability : experimental
Portability : POSIX, macOS, Windows
Some useful functions lifted to monadic actions.
-}
module Utils.Monad where
-- | If the boolean resolves to True, returns the first argument, else the
-- second.
ifM :: Monad m => m Bool -> m a -> m a -> m a
ifM b t e = b >>= \b' -> if b' then t else e
-- | Runs the monadic action only if the boolean resolves to True.
whenM :: Monad m => m Bool -> m () -> m ()
whenM b t = ifM b t (return ())
-- | whenJust m a = when (isJust m) (a (fromJust m)), but with less
-- fromJust.
whenJust :: Monad m => Maybe a -> (a -> m ()) -> m ()
whenJust = flip (maybe (return ()))
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