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1. parseMaybe :: (Ord e, Stream s) => Parsec e s a -> s -> Maybe a

   megaparsec	Text.Megaparsec

   parseMaybe p input runs the parser p on input and returns the result inside Just on success and Nothing on failure. This function also parses eof, so if the parser doesn't consume all of its input, it will fail. The function is supposed to be useful for lightweight parsing, where error messages (and thus file names) are not important and entire input should be consumed. For example, it can be used for parsing of a single number according to a specification of its format.

2. waitBarrierMaybe :: Barrier a -> IO (Maybe a)

   extra	Control.Concurrent.Extra

   A version of waitBarrier that never blocks, returning Nothing if the barrier has not yet been signaled.

3. fromMaybeM :: Monad m => m a -> m (Maybe a) -> m a

   extra	Control.Monad.Extra

   Monadic generalisation of fromMaybe.

4. mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]

   extra	Control.Monad.Extra

   A version of mapMaybe that works with a monadic predicate.

5. whenMaybe :: Applicative m => Bool -> m a -> m (Maybe a)

   extra	Control.Monad.Extra

   Like when, but return either Nothing if the predicate was False, or Just with the result of the computation.

   whenMaybe True  (print 1) == fmap Just (print 1)
   whenMaybe False (print 1) == pure Nothing
   

6. whenMaybeM :: Monad m => m Bool -> m a -> m (Maybe a)

   extra	Control.Monad.Extra

   Like whenMaybe, but where the test can be monadic.

7. eitherToMaybe :: Either a b -> Maybe b

   extra	Data.Either.Extra

   Given an Either, convert it to a Maybe, where Left becomes Nothing.

   \x -> eitherToMaybe (Left x) == Nothing
   \x -> eitherToMaybe (Right x) == Just x
   

8. eitherToMaybe :: Either a b -> Maybe b

   extra	Extra

   Given an Either, convert it to a Maybe, where Left becomes Nothing.

   \x -> eitherToMaybe (Left x) == Nothing
   \x -> eitherToMaybe (Right x) == Just x
   

9. fromMaybeM :: Monad m => m a -> m (Maybe a) -> m a

   extra	Extra

   Monadic generalisation of fromMaybe.

10. mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]

    extra	Extra

    A version of mapMaybe that works with a monadic predicate.

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