| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell98 |
Data.Maybe.HT
Documentation
>>>import Control.Monad (guard)
toMaybe :: Bool -> a -> Maybe a Source #
Returns Just if the precondition is fulfilled.
prop> b x -> (guard b >> x) == (toMaybe b =<< (x::Maybe Char))
(?->) :: Maybe a -> (a -> b) -> Maybe b infixl 6 Source #
This is an infix version of fmap
for writing select style expressions
using test functions, that produce Maybes.
The precedence is chosen to be higher than (:),
in order to allow:
alternatives default $ checkForA ?-> (\a -> f a) : checkForB ?-> (\b -> g b) : []
The operation is left associative in order to allow to write
checkForA ?-> f ?-> g
which is equivalent to
checkForA ?-> g . f
due to the functor law.
alternatives :: a -> [Maybe a] -> a Source #