Modulerelude-1.2.0.0Haskell2010

Relude.Monad.Maybe

SPDX-License-Identifier : MIT Maintainer : Kowainik xrom.xkov@gmail.com Stability : Stable Portability : Portable

Utility functions to work with Relude.Maybe data type as monad.

8 values

Packagerelude-1.2.0.0
Exports8
LanguageHaskell2010
LicenceMIT
SourceMaybe.hs

Combinators

5 declarations

value(?:) :: Maybe a -> a -> a

Similar to fromMaybe but with flipped arguments.

Example1 expression

>>> readMaybe "True" ?: FalseTrue

Example1 expression

>>> readMaybe "Tru" ?: FalseFalse

valuewhenJust :: Applicative f => Maybe a -> (a -> f ()) -> f ()

Specialized version of Relude.for_ for Maybe. It's used for code readability.

Also helps to avoid space leaks: Foldable.mapM_ space leak.

Example2 expressions

>>> whenJust Nothing $ \b -> print (not b)>>> whenJust (Just True) $ \b -> print (not b)False

valuewhenJustM :: Monad m => m (Maybe a) -> (a -> m ()) -> m ()

Monadic version of whenJust.

Example2 expressions

>>> whenJustM (pure Nothing) $ \b -> print (not b)>>> whenJustM (pure $ Just True) $ \b -> print (not b)False

valuewhenNothing :: Applicative f => Maybe a -> f a -> f a

Performs default Applicative action if Nothing is given. Otherwise returns content of Just pured to Applicative.

Example2 expressions

>>> whenNothing Nothing [True, False][True,False]>>> whenNothing (Just True) [True, False][True]

valuewhenNothing_ :: Applicative f => Maybe a -> f () -> f ()

Performs default Applicative action if Nothing is given. Do nothing for Just. Convenient for discarding Just content.

Example2 expressions

>>> whenNothing_ Nothing $ putTextLn "Nothing!"Nothing!>>> whenNothing_ (Just True) $ putTextLn "Nothing!"

Monadic combinators

3 declarations

valuewhenNothingM :: Monad m => m (Maybe a) -> m a -> m a

Monadic version of whenNothing.

Example2 expressions

>>> whenNothingM (pure $ Just True) $ True <$ putTextLn "Is Just!"True>>> whenNothingM (pure Nothing) $ False <$ putTextLn "Is Nothing!"Is Nothing!False

valuewhenNothingM_ :: Monad m => m (Maybe a) -> m () -> m ()

Monadic version of whenNothing_.

Example2 expressions

>>> whenNothingM_ (pure $ Just True) $ putTextLn "Is Just!">>> whenNothingM_ (pure Nothing) $ putTextLn "Is Nothing!"Is Nothing!

valuemapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]

The monadic version of the mapMaybe function.

Example1 expression

>>> :{evenInHalf :: Int -> IO (Maybe Int)evenInHalf n    | even n = pure $ Just $ n `div` 2    | otherwise = pure Nothing:}

Example1 expression

>>> mapMaybeM evenInHalf [1..10][1,2,3,4,5]