Data.Maybe.HT

Documentation

toMaybe :: Bool -> a -> Maybe a

Returns Just if the precondition is fulfilled.

(?->) :: Maybe a -> (a -> b) -> Maybe b

This is an infix version of fmap for writing Data.Bool.HT.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