#include <cassert>
#include <string>

/** TESTCASES **/

int fun1(std::string const& str)
{
    return std::stoi(str);
}

char fun2(int x)
{
    return static_cast<char>(x);
}

struct NextCharacter
{
    char operator()(char c) const { return c + 1; }
};

int main()
{

    assert((payload(1) | [](int    x) -> double { return 1.5f + x; }
                       | [](double y) -> int    { return 2*y; }) == 5);

    assert((payload("67") | fun1 | fun2) == 'C');

    char c { 'a' };
    assert((payload(c) | NextCharacter{}) == 'b');
}