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A continuation-passing variant of Maybe for short-circuiting at failure. This is based largely on code from the Haskell Wiki (http://www.haskell.org/haskellwiki/Performance/Monads) which was released under a simple permissive license (http://www.haskell.org/haskellwiki/HaskellWiki:Copyrights). However, various changes and extensions have been made, which are subject to the BSD license of this package.
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unification-fd Control.Monad.MaybeK A continuation-passing encoding of Maybe; also known as Codensity Maybe, if you're familiar with that terminology. N.B., this is not the 2-continuation implementation based on the Church encoding of Maybe. The latter tends to have worse performance than non-continuation based implementations. This is generally more efficient than using Maybe for two reasons. First is that it right associates all binds, ensuring that bad associativity doesn't artificially introduce midpoints in short-circuiting to the nearest handler. Second is that it removes the need for intermediate case expressions. N.B., the Alternative and MonadPlus instances are left-biased in a. Thus, they are not commutative.
data
MaybeKT (m :: Type -> Type) aunification-fd Control.Monad.MaybeK A monad transformer version of MaybeK.
type
MaybeMaybeManageHook = Query Maybe Maybe Endo WindowSetxmonad-contrib XMonad.Hooks.FloatConfigureReq A variant of MaybeManageHook that additionally may or may not make changes to the WindowSet.
type
MaybeManageHook = Query Maybe Endo WindowSetxmonad-contrib XMonad.Hooks.ManageHelpers A ManageHook that may or may not have been executed; the outcome is embedded in the Maybe
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base Data.Maybe The maybeToList function returns an empty list when given Nothing or a singleton list when given Just.
Examples
Basic usage:>>> maybeToList (Just 7) [7]
>>> maybeToList Nothing []
One can use maybeToList to avoid pattern matching when combined with a function that (safely) works on lists:>>> import GHC.Internal.Text.Read ( readMaybe ) >>> sum $ maybeToList (readMaybe "3") 3 >>> sum $ maybeToList (readMaybe "") 0
maybeNew :: (a -> IO (Ptr b)) -> Maybe a -> IO (Ptr b)base Foreign.Marshal.Utils Allocate storage and marshal a storable value wrapped into a Maybe
maybePeek :: (Ptr a -> IO b) -> Ptr a -> IO (Maybe b)base Foreign.Marshal.Utils Convert a peek combinator into a one returning Nothing if applied to a nullPtr
maybeWith :: (a -> (Ptr b -> IO c) -> IO c) -> Maybe a -> (Ptr b -> IO c) -> IO cbase Foreign.Marshal.Utils Converts a withXXX combinator into one marshalling a value wrapped into a Maybe, using nullPtr to represent Nothing.
maybeToExceptT :: forall (m :: Type -> Type) e a . Functor m => e -> MaybeT m a -> ExceptT e m atransformers Control.Monad.Trans.Maybe Convert a MaybeT computation to ExceptT, with a default exception value.