Extensions to the Maybe API, which utilise typeclasses.
fold : Typeclasses.Classes.Monoid.Monoid a -> Maybe a -> a
Extract a value or use the Monoid's identity.
foldMap : Typeclasses.Classes.Monoid.Monoid b -> (a -> b) -> Maybe a -> b
Map the element of Maybe to a type which has an instance of Monoid
,
or use its identity, when Maybe is Nothing.