Monads and do-notation in C ++

In Haskell, as we know, there are monads, but in C ++ there are none. But nothing prevents to implement monads in C ++. Let's see if we have everything necessary for their implementation:

• Passing a function as an argument to another function is.
• Lambda functions are present in C ++ 11. I'm not sure that they are necessary for the implementation of monads, but with them, of course, easier.
• Type classes are not. In C ++, we wanted to add their analogue - concepts, but have not added it yet. But for the implementation of monads, they are not needed, you can simply overload functions or operators for specific monads.
• do-notation In C ++, it is not there, but it is not needed for the implementation of monads, although it makes their use much more convenient. There is already a proposal to add its counterpart to the standard, but more on that below.

The monad in Haskell is defined as follows:

class Monad m where (>>= ) ::ma -> (a->mb)->mb (>> ) ::m a->m b->mb return ::a->ma fail::String->ma 

First, let's take some abstract monad, let it be of type in C ++

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
      ?  ,    ,      :           resumable ,  ,   Fibers  Windows  boost::coroutine .    ,     .     resumable   -     ,    await . ,   await    then       ,    await .    resumable     std::future ,          then  get .         C++,        ,    ,  ,   .            std::future . 
  ,    resumable       .        ,     resumable     . 

Monad. , .
template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

template<typename A> Monad <A> mreturn(A a) { ... // } return C++, mreturn. , a .
fail , .

, C++, - . - Maybe , ., std::future . C++11. future T , . , , - , , , , . future get .
template<class T> class future { public: ... T get(); // get ... };
C++11 – std::async . , std::future . : future<int> result = async(f); // - f int a = result.get(); // f .
mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
async([&] () -> B { return f(a).get(); }) == f(a) , , f , . , f , ( ).

: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
>>= , std::future then . , A , future. , , future , then , .
unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

? , , : resumable , , Fibers Windows boost::coroutine . , . resumable - , await . , await then , await . resumable std::future , then get . C++, , , , . std::future .
, resumable . , resumable .

 Monad. ,     . 
 template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... //     }       ma,    f    f. 
 
 template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }     >>= ,        .       ( m >> k = m >>= \_ -> k ),     Haskell  C++. 
 
 template<typename A> Monad <A> mreturn(A a) { ... //     }  return    C++,      mreturn.     ,     a       . 
  fail    ,        . 
 
 ,        C++,    -        .         - Maybe ,   .,     std::future .      C++11.   future       T ,     .   , ,   -   ,      ,   ,  ,      .    future      get . 
 template<class T> class future { public: ... T get(); //  get         ... }; 
   C++11    – std::async .      ,           std::future .       : future<int> result = async(f); //  -      f int a = result.get(); //    f    . 
        mreturn  >>=   std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); }  ,       future      ,   .     ,    . 
 
 template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); }   ,    ,         ma,       f,         f. 
 
  ,      .    3 ,     : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g) 
     C++, : 
 (mreturn(a) >>= f) == f(a)   , : 
 async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) ,  mreturn(a).get()   ,   .     a  std::future ,     . , : 
 async([&] () -> B { return f(a).get(); }) == f(a)  ,  ,     f ,        .   ,   f  ,      (   ). 
 
  : m >>= mreturn == m   , : 
 async([&] () -> B { return mreturn(m.get()).get(); }) == m      mreturn(x).get() , : 
 async([&] () -> B { return m.get(); }) == m  ,     m.    ,        m. 
 
  : (m >>= f) >>= g == m >>= (\x -> fx >>= g)       ,   ,   .      m   f,   ,      m.       g,     f.     f  g             m. 
 
    .    -     : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a;   ,    5  11. 
 
  C++11      mreturn  >>=.      : n3721 
  mreturn  make_ready_future . 
  >>= ,    std::future   then .     ,       A ,   future.     ,        ,   future    ,   then ,   . 
     unwrap      future<future>  future.   join  Control.Monad  . 
 
  then     : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); }     ,   ,          .       resumable : n3722 .        : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); }   resumable ,    ,    ,       .     await –     ( <- )  do   . ,   str.read  f    future,      await  int ,       . 
 
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template<typename A, typename B> Monad<B> operator>>=(Monad<A> ma, function<Monad<B> (A)> f) { ... // } ma, f f.

template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; } >>= , . ( m >> k = m >>= \_ -> k ), Haskell C++.

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mreturn >>= std::future #include <future> using namespace std; template<typename A> future<A> mreturn(const A& a) { return async([=]{ return a; }); } , future , . , .

template<typename A, typename B> future<B> operator>>=(future<A>& ma, const function<future<B> (A)>& f) { return async([&] () -> B { return f(ma.get()).get(); }); } , , ma, f, f.

, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)
C++, :
(mreturn(a) >>= f) == f(a) , :
async([&] () -> B { return f(mreturn(a).get()).get(); }) == f(a) , mreturn(a).get() , . a std::future , . , :
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: m >>= mreturn == m , :
async([&] () -> B { return mreturn(m.get()).get(); }) == m mreturn(x).get() , :
async([&] () -> B { return m.get(); }) == m , m. , m.

: (m >>= f) >>= g == m >>= (\x -> fx >>= g) , , . m f, , m. g, f. f g m.

. - : function<future<int> (int)> f = [](int a){ cout << a << '\n'; return mreturn(a + 6); }; int a = (mreturn(5) >>= f).get(); cout << a; , 5 11.

C++11 mreturn >>=. : n3721
mreturn make_ready_future .
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unwrap future<future> future. join Control.Monad .

then : future<int> f(shared_ptr<stream> str) { shared_ptr<vector<char>> buf = ...; return str->read(512, buf).then([](future<int> op) { return op.get() + 11; }); } future<void> g() { shared_ptr<stream> s = ...; return f(s).then([s](future<int> op) { s->close(); }); } , , . resumable : n3722 . : future<int> f(stream str) resumable { shared_ptr<vector<char>> buf = ...; int count = await str.read(512, buf); return count + 11; } future<void> g() resumable { stream s = ...; int pls11 = await f(s); s.close(); } resumable , , , . await – ( <- ) do . , str.read f future, await int , .

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