is also considered to be a
polymorphic operator on functions
with the type
F : (a -@# b) -@# (F a -@# F b).
Functors are a generalisation of the function "
map". The
type operator in this case takes a type T and returns type
"list of T". The map function takes a function and applies it
to each element of a list.
(1995-02-07)