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  1. greadMaybe :: GRead t => String -> (forall (a :: k) . () => t a -> b) -> Maybe b

    some Data.GADT.Show 

    >>> greadMaybe "InL Refl" mkSome :: Maybe (Some (Sum ((:~:) Int) ((:~:) Bool)))
Just (mkSome (InL Refl))

    >>> greadMaybe "L1 Refl" mkSome :: Maybe (Some ((:~:) Int :+: (:~:) Bool))
Just (mkSome (L1 Refl))

    >>> greadMaybe "garbage" mkSome :: Maybe (Some ((:~:) Int))
Nothing

  2. threadMaybe :: (i -> r -> a) -> Split t i r -> SplitM t j i -> SplitM t j a

    fgl Data.Graph.Inductive.Internal.Thread

    No documentation available.

  3. threadMaybe' :: (r -> a) -> Split t i r -> Split t j (Maybe i) -> Split t j (Maybe a)

    fgl Data.Graph.Inductive.Internal.Thread

    No documentation available.

  4. timeoutMaybe :: Exception e => Maybe Int -> e -> IO a -> IO a

    network-transport Network.Transport.Internal

    If the timeout value is not Nothing, wrap the given computation with a timeout and it if times out throw the specified exception. Identity otherwise.

  5. leftToMaybe :: Either l r -> Maybe l

    relude Relude.Monad.Either

    Maps left part of Either to Maybe. 

    >>> leftToMaybe (Left True)
Just True

>>> leftToMaybe (Right "aba")
Nothing

  6. rightToMaybe :: Either l r -> Maybe r

    relude Relude.Monad.Either

    Maps right part of Either to Maybe. 

    >>> rightToMaybe (Left True)
Nothing

>>> rightToMaybe (Right "aba")
Just "aba"

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

    relude Relude.Monad.Maybe

    The monadic version of the mapMaybe function. 

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

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

  8. catMaybes :: [Maybe a] -> [a]

    relude Relude.Monad.Reexport

    The catMaybes function takes a list of Maybes and returns a list of all the Just values.

    Examples

    Basic usage: 
    >>> catMaybes [Just 1, Nothing, Just 3]
[1,3]
    When constructing a list of Maybe values, catMaybes can be used to return all of the "success" results (if the list is the result of a map, then mapMaybe would be more appropriate): 
    >>> import GHC.Internal.Text.Read ( readMaybe )

>>> [readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
[Just 1,Nothing,Just 3]

>>> catMaybes $ [readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
[1,3]

  9. exceptToMaybeT :: forall (m :: Type -> Type) e a . Functor m => ExceptT e m a -> MaybeT m a

    relude Relude.Monad.Reexport

    Convert a ExceptT computation to MaybeT, discarding the value of any exception.

  10. fromMaybe :: a -> Maybe a -> a

    relude Relude.Monad.Reexport

    The fromMaybe function takes a default value and a Maybe value. If the Maybe is Nothing, it returns the default value; otherwise, it returns the value contained in the Maybe.

    Examples

    Basic usage: 
    >>> fromMaybe "" (Just "Hello, World!")
"Hello, World!"

    >>> fromMaybe "" Nothing
""
    Read an integer from a string using readMaybe. If we fail to parse an integer, we want to return 0 by default: 
    >>> import GHC.Internal.Text.Read ( readMaybe )

>>> fromMaybe 0 (readMaybe "5")
5

>>> fromMaybe 0 (readMaybe "")
0

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