functor

In category theory, a functor F is an operator on types. F

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)