gistfile1.cpp

#include <cstdio>
#include <stdexcept>

template <class T>
struct Maybe {
    Maybe( const T& val ) : val_(val), valid_(true) { }
    Maybe() : valid_(false) { }
    const T& get() const { 
        if (valid_) return val_;
        throw std::logic_error("lol type systems");
    }
private:
    T val_;
    bool valid_; 
};

template <class T> 
Maybe<T> Just(const T& val) {
    return Maybe<T>(val);
}

template <class T> 
Maybe<T> Nothing() { 
    return Maybe<T>(); 
}

Maybe<int> isYouPositive(int x)
{
    if (x > 0) return Just(x);
    return Nothing<int>();
}

int main(void)
{
    auto a = isYouPositive(1);
    printf("%d\n", a.get());
    auto b = isYouPositive(-1);
    printf("%d\n", b.get());

}