Algebraic programming in C++

This is my hobby C++ programming project. I have no plans to invest time in
turning anything in this project into reusable libraries and I make absolutely
no promises of any kind regarding the future of this project.

The idea is to experiment with algebraic programming techniques in C++. First of
all, I want to be able to program conveniently with structural algebraic types
(i.e. sums, products, …) and use algebraic structures (i.e. monoids, monads,
…). Then I want to use those to implement a language with algebraic effects. I
want everything to be as composable as possible.