Manually recreating flow-control constructs using lambdas and goto

manual_flow_constructs.c++

template <typename Predicate, typename Body>
constexpr void While(Predicate pred, Body body) {
    goto predicate;
loop:
    body();
predicate:
    if (pred()) { goto loop; }
}

template <typename Body, typename Predicate>
constexpr void DoWhile(Body body, Predicate pred) {
loop:
    body();
    if (pred()) { goto loop; }
}

template <typename Init, typename Pred, typename Mod, typename Body>
constexpr void For(Init init, Pred pred, Mod mod, Body body) {
    init();
    goto predicate;
loop:
    body();
    mod();
predicate:
    if (pred()) { goto loop; }
}

#include <iostream>

int main() {
    int x = 0;
    While([&]{ return x < 5; }, [&]{
        std::cout << x << " ";
        ++x;
    });
    std::cout << "\n";
    DoWhile([&]{
        std::cout << x << " ";
        ++x;
    }, [&]{ return x < 10; });
    std::cout << "\n";
    For([&]{ x = 0; }, [&]{ return x < 5; }, [&]{ ++x; }, [&]{
        std::cout << x << " ";
    });
    std::cout << "\n";
    return x;
}