In Functional Programming, what is a functor?

Question

I\'ve come across the term \'Functor\' a few times while reading various articles on functional programming, but the authors typically assume the reader already understands

Answer 1

Other answers here are complete, but I'll try another explanation of the FP use of functor. Take this as analogy:

A functor is a container of type a that, when subjected to a function that maps from a→b, yields a container of type b.

Unlike the abstracted-function-pointer use in C++, here the functor is not the function; rather, it's something that behaves consistently when subjected to a function.