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1. fromMaybe :: a -> Maybe a -> a

   foundation	Foundation

   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
   

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

   foundation	Foundation

   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]
   

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

   foundation	Foundation

   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]
   

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

   foundation	Foundation.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.

5. lowerMaybe :: Monoid m => Maybe' m -> m

   generic-data	Generic.Data.Internal.Traversable

   No documentation available.

6. splitTyConApp_maybe :: HasDebugCallStack => Type -> Maybe (TyCon, [Type])

   ghc-typelits-presburger	GHC.TypeLits.Presburger.Compat

   Attempts to tease a type apart into a type constructor and the application of a number of arguments to that constructor

7. tyConAppTyCon_maybe :: Type -> Maybe TyCon

   ghc-typelits-presburger	GHC.TypeLits.Presburger.Compat

   The same as fst . splitTyConApp We can short-cut the FunTy case

8. windowInvalidateMaybeRecurse :: (HasCallStack, MonadIO m, IsWindow a) => a -> Region -> Maybe WindowChildFunc -> m ()

   gi-gdk3	GI.Gdk.Objects.Window

   Adds region to the update area for window. The update area is the region that needs to be redrawn, or “dirty region.” The call windowProcessUpdates sends one or more expose events to the window, which together cover the entire update area. An application would normally redraw the contents of window in response to those expose events. GDK will call windowProcessAllUpdates on your behalf whenever your program returns to the main loop and becomes idle, so normally there’s no need to do that manually, you just need to invalidate regions that you know should be redrawn. The childFunc parameter controls whether the region of each child window that intersects region will also be invalidated. Only children for which childFunc returns TRUE will have the area invalidated.

9. warnMaybe :: Warn a -> Maybe a

   markup-parse	MarkupParse

   Returns results, if any, ignoring warnings.

   >>> warnMaybe $ (tokenize Html) "<foo><baz"
   Just [OpenTag StartTag "foo" []]
   

10. prop_smapMaybe :: forall r ix e a . (Eq a, Show a, Stream r ix e, Foldable (Array r ix)) => Array r ix e -> Fun e (Maybe a) -> Property

    massiv-test	Test.Massiv.Array.Delayed

    No documentation available.

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