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1. maybeK :: b -> (a -> b) -> MaybeK a -> b

   unification-fd	Control.Monad.MaybeK

   A version of maybe for convenience. This is almost identical to mplus but allows applying a continuation to Just values as well as handling Nothing errors. If you only want to handle the errors, use mplus instead.

2. maybeMatch :: (a -> b) -> a -> Maybe b

   unipatterns	UniPatterns

   Run a function returning Nothing if function fails to pattern match.

   >>> maybeMatch (\[a] -> a + 10) [5]
   Just 15
   
   >>> maybeMatch (\[a] -> a + 10) []
   Nothing
   
   >>> maybeMatch (\[a] -> a + 10) [1, 2, 3]
   Nothing
   

3. maybeToEither :: a -> Maybe b -> Either a b

   verset	Verset

   Given a Maybe, convert it to an Either, providing a suitable value for the Left should the value be Nothing.

   \a b -> maybeToEither a (Just b) == Right b
   \a -> maybeToEither a Nothing == Left a
   

4. maybeManageDebug :: ManageHook

   xmonad-contrib	XMonad.Hooks.ManageDebug

   manageDebug only if the user requested it with debugNextManagedWindow.

5. maybeToDefinite :: (Monoid a, Functor m) => m (Maybe a) -> m a

   xmonad-contrib	XMonad.Hooks.ManageHelpers

   converts MaybeManageHooks to ManageHooks

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

   base	Data.Maybe

   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]
   

7. fromMaybe :: a -> Maybe a -> a

   base	Data.Maybe

   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
   

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

   base	Data.Maybe

   The listToMaybe function returns Nothing on an empty list or Just a where a is the first element of the list.

   Examples

   Basic usage:

   >>> listToMaybe []
   Nothing
   

   >>> listToMaybe [9]
   Just 9
   

   >>> listToMaybe [1,2,3]
   Just 1
   

   Composing maybeToList with listToMaybe should be the identity on singleton/empty lists:

   >>> maybeToList $ listToMaybe [5]
   [5]
   
   >>> maybeToList $ listToMaybe []
   []
   

   But not on lists with more than one element:

   >>> maybeToList $ listToMaybe [1,2,3]
   [1]
   

9. mapMaybe :: (a -> Maybe b) -> [a] -> [b]

   base	Data.Maybe

   The mapMaybe function is a version of map which can throw out elements. In particular, the functional argument returns something of type Maybe b. If this is Nothing, no element is added on to the result list. If it is Just b, then b is included in the result list.

   Examples

   Using mapMaybe f x is a shortcut for catMaybes $ map f x in most cases:

   >>> import GHC.Internal.Text.Read ( readMaybe )
   
   >>> let readMaybeInt = readMaybe :: String -> Maybe Int
   
   >>> mapMaybe readMaybeInt ["1", "Foo", "3"]
   [1,3]
   
   >>> catMaybes $ map readMaybeInt ["1", "Foo", "3"]
   [1,3]
   

   If we map the Just constructor, the entire list should be returned:

   >>> mapMaybe Just [1,2,3]
   [1,2,3]
   

10. bitSizeMaybe :: Bits a => a -> Maybe Int

    base	Data.Bits

    Return the number of bits in the type of the argument. The actual value of the argument is ignored. Returns Nothing for types that do not have a fixed bitsize, like Integer.

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