Path 1 to implement the State monad in C++ using Church Free

state_church_free.h

# This is a sample of how to implement the State monad with Church Free monad.
# This sample is incomplete, but its concept is taken from my Free-monad based STM library.
# Consider the library to implement the rest of the code. The idea is the same.

# https://github.com/graninas/cpp_stm_free

#include <functional>
#include <variant>
#include <any>

using Any = std::any;

using Unit = int;

template <typename A, typename Next>
struct Put
{
    A val;
    std::function<Next(Unit)> next;
};

template <typename A, typename Next>
struct Get
{
    std::function<Next(A)> next;
};

template <typename Next>
using PutA = Put<Any, Next>;

template <typename Next>
using GetA = Get<Any, Next>;


template <class Ret>
struct STMF
{
    std::variant<
        GetA<Ret>,
        PutA<Ret>
    > stmf;
};

template <typename A>
using StmlFunc = std::function<
        Any(
            std::function<Any(A)>,
            std::function<Any(STMF<Any>)>
        )>;

template <typename A>
struct STML
{
    StmlFunc<A> runF;
};