gistfile1.cpp

$ g++ -c monads.cc
monads.cc: In member function ‘lvector<B> Monad<lvector>::bind(lvector<A>, Function)’:
monads.cc:24: error: expected `;' before ‘it_a’
monads.cc:26: error: ‘it_a’ was not declared in this scope
monads.cc:28: error: expected `;' before ‘it_b’
monads.cc:28: error: ‘it_b’ was not declared in this scope


#include <string>
#include <vector>

template <template <typename> class M>
class Monad {
  template <typename A, typename B, typename Function>
  M<B> bind(M<A> in, Function function);

  template <typename T>
  M<T> m_return(T data);

  template <typename T>
  M<T> fail(std::string message);
};

template <typename T>
class lvector : public std::vector<T> {
};

template <>
class Monad<lvector> {
  template <typename A, typename B, typename Function>
  lvector<B> bind(lvector<A> in, Function function) {
    lvector<B> result;
    for (lvector<A>::iterator it_a = in.begin(); it_a != in.end(); ++it_a) {
      lvector<B> partial_result = function(*it_a);
      for (lvector<B>::iterator it_b = partial_result.begin(); it_b != partial_result.end(); ++it_b) {
        result.push_back(*it_b);
      }
    }
    return result;
  }

  template <typename T>
  lvector<T> m_return(T data) {
    lvector<T> result;
    result.push_back(data);
    return result;
  }

  template <typename T>
  lvector<T> fail(std::string message) {
    return lvector<T>();
  }
};