Created
September 6, 2013 15:35
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General Maybe monad in C++
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| #include <iostream> | |
| #include <cassert> | |
| #include <cmath> | |
| using namespace std; | |
| template<typename a> class Maybe | |
| { | |
| public: | |
| static Maybe<a> Just(a value) { return Maybe(value); } | |
| static Maybe<a> Nothing() { return Maybe(); } | |
| bool isJust() { return m_valid; } | |
| a getJust() { assert(isJust()); return m_value; } | |
| template<typename b> Maybe<b> operator>>=(Maybe<b> (*f)(int)) { | |
| return isJust() ? f(getJust()) : Maybe<b>::Nothing(); | |
| } | |
| Maybe<a> unit(a value) { return Maybe(value); } | |
| void show() { | |
| if(isJust()) | |
| cout << "Just " << getJust() << endl; | |
| else | |
| cout << "Nothing" << endl; | |
| } | |
| private: | |
| Maybe() : m_value(0), m_valid(false) {} | |
| Maybe(a value) : m_value(value), m_valid(true) {} | |
| a m_value; | |
| bool m_valid; | |
| }; | |
| Maybe<int> IM_Square(int a) { return (abs(a) >= 0x8000) ? Maybe<int>::Nothing() : Maybe<int>::Just(a * a); } | |
| int main(int argc, char** argv) | |
| { | |
| Maybe<int> result = Maybe<int>::Nothing(); | |
| result = Maybe<int>::Just(0x4000) >>= IM_Square; | |
| result.show(); | |
| result = (Maybe<int>::Just(0x4000) >>= IM_Square) >>= IM_Square; | |
| result.show(); | |
| return 0; | |
| } |
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