Functors

What are functors?

We need to be a little careful, as the term functor has different meanings in different branches of computing. For example, it is sometimes used simply to refer to a function object. That is not what we mean here.

If you are familiar with the Haskell programming language, oslash functors are based closely on those.

A functor is an object that wraps a value and provides a map method that can be used to apply a function to that value.

Most of the functors we discuss in this section are also ...