Proof that some Maybe is actually Just
An optional value. This can be used to represent the possibility of
failure, where a function may return a value, or not.
Transform any semigroup into a monoid by using Nothing as the
designated neutral element and collecting the contents of the
Just constructors using a semigroup structure on a. This is
the behaviour in the Haskell libraries.
Convert a Maybe a value to an a value by providing a default a value
in the case that the Maybe value is Nothing.
Decide whether a 'Maybe' is 'Just'
Convert a Maybe a value to an a value, using neutral in the case
that the Maybe value is Nothing.
Returns Nothing when applied to neutral, and Just the value otherwise.
Returns Just the given value if the conditional is True
and Nothing if the conditional is False.