utility-ht-0.0.6: Various small helper functions for Lists, Maybes, Tuples, Functions




toMaybe :: Bool -> a -> Maybe aSource

Returns Just if the precondition is fulfilled.

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

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] -> aSource