Maybe and Either Monads in Plain C++ 17

Where sizeable libraries with complex template metaprogramming were previously required to facilitate functional programming in C++, we demonstrate that simple monads can be implemented in a compact and relatively straightforward manner in C++ 17. Along with general discussion of functional programming in C++, and a brief review of functional programming itself, the Maybe and Either monads are described and implemented using C++ 17features. We look superficially at the trend toward functional programming apparent in the standards proposals and the evolution of the ISO C++ standard.