Category "functor"

Implementing applicative functor for custom data type with two identical type classes

I'm trying to make Twice a member of applicative, but I am getting "Conflicting definitions for `a'" in the functor implementation: Also I'm not sure how to imp

Is there a concise/inline way to create Set values without explicitly naming their type?

In most language that have parametric / generic types, there is a (type) expression you can write to mean 'Set of something'. E.g. Set<Integer> in Java. S

Use of a functor on for_each

Why does the for_each call on functor doesn't update sum::total at the end? struct sum { sum():total(0){}; int total; void operator()(int element)