Maybe in C++

Maybe.cpp

#include <string>
#include <functional>

using namespace std;

template <typename T>
struct Maybe{
  T just;
  bool isNothing;
};

template <typename T>
Maybe<T>* makeMaybe(T just, bool isNothing){
  Maybe<T>* maybe = (struct Maybe<T>*) malloc (sizeof(struct Maybe<T>));
  maybe->just = just;
  maybe->isNothing = isNothing;
  return maybe;
}

template <typename T>
Maybe<T>* Just(T just){
  return makeMaybe(just, false);
}

template <typename T>
Maybe<T>* Nothing(){
  return makeMaybe((T) 0, true);
}

template <typename T>
bool isNothing(Maybe<T>* maybe){
  return maybe == NULL || maybe->isNothing;
}

template <typename T>
string toString(Maybe<T>* maybe){
  return isNothing(maybe) ? "Nothing" : "Just " + to_string(maybe->just);
}

template <typename A, typename B>
Maybe<B>* map (function<B(A)> f, Maybe<A>* maybe){
  return isNothing(maybe) ? Nothing<B>() : Just(f(maybe->just));
}

template <typename A, typename B>
Maybe<B>* operator >>= (Maybe<A>* maybe, function<Maybe<B>*(A)> f){
  return isNothing(maybe) ? Nothing<B>() : f(maybe->just);
}

Compare with equivalent in Elm:

type Maybe a = Nothing | Just a

map : (a -> b) -> Maybe a -> Maybe b
map f maybe =
  case maybe of
    Nothing -> Nothing
    Just x  -> Just (f x)


(>>=) : Maybe a -> (a -> Maybe b) -> Maybe b
(>>=) maybe f =
  case maybe of
    Nothing -> Nothing
    Just x  -> f x