C ++のモナドとdo記法

ご存じのように、Haskellにはモナドがありますが、C ++にはありません。 しかし、C ++でのモナドの実装を妨げるものは何もありません。 実装に必要なものがすべて揃っているかどうかを見てみましょう。

• 関数を引数として別の関数に渡すことはそうです。
• Lambda関数-はい、C ++ 11で追加されました。 モナドの実装に必要かどうかはわかりませんが、モナドの方が間違いなく簡単です。
• 型クラス-いいえ。 C ++では、彼らは彼らのアナログ-概念を追加したかったが、まだ追加していない。 しかし、モナドの実装には必要ありません。特定のモナドの関数や演算子を単純にオーバーロードできます。
• 表記を行います。 C ++では不要ですが、モナドの実装には必要ありませんが、モナドの使用はより便利になります。 アナログを標準に追加する提案はすでにありますが、それについては以下で詳しく説明します。

Haskellのモナドは次のように定義されます。

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

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

最初に、C ++で型を持っている場合でも、いくつかの抽象モナドを見てみましょう

 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
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      >>=
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    std::future
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       then
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .     ,       A
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   future.     ,        ,   future    ,   then
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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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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     ,  ,   Fibers  Windows  boost::coroutine
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ,     .     resumable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     . ,   await
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .    resumable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         std::future
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,          then
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      get
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         C++,        ,    ,  ,   .            std::future
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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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



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fail



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, C++, - . - Maybe



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get



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template<class T> class future { public: ... T get(); // get ... };





C++11 – std::async



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. : 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()



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async([&] () -> B { return f(a).get(); }) == f(a)



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: m >>= mreturn == m



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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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future<future> future. join



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: 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



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 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
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,     m.    ,        m. 
      

        
        
        
      

     
      

        
        
        
      

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        .    -     : 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
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         ,   ,          .       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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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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++.



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, . 3 , : Left identity : return a >>= f == fa Right identity: m >>= return == m Associativity: (m >>= f) >>= g == m >>= (\x -> fx >>= g)





C++, :

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, 5 11.



C++11 mreturn >>=. : n3721

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, , . 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(); }



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           ma,    f    f. 
      

        
        
        
      

     
      

        
        
        
      

     template<typename A, typename B> Monad<B> operator>>(Monad<A> ma, Monad<B> mb) { return Ma >>= [=](A){ return mb; }; }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ),     Haskell  C++. 
      

        
        
        
      

     
      

        
        
        
      

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       ,    5  11. 
      

        
        
        
      

     
      

        
        
        
      

      C++11      mreturn  >>=.      : n3721 
      

        
        
        
      

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         : 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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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Monad. , .

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



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       ,    5  11. 
      

        
        
        
      

     
      

        
        
        
      

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       ,    5  11. 
      

        
        
        
      

     
      

        
        
        
      

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         : 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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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, , . 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(); }



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Monad. , .

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



ma, f f.



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, 5 11.



C++11 mreturn >>=. : n3721

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, , . 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(); }



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      ,       future      ,   .     ,    . 
      

        
        
        
      

     
      

        
        
        
      

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        .    -     : 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 
      

        
        
        
      

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         : 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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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, , . 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(); }



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     ),     Haskell  C++. 
      

        
        
        
      

     
      

        
        
        
      

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

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     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. 
      

        
        
        
      

     
      

        
        
        
      

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         C++, : 
      

        
        
        
      

     (mreturn(a) >>= f) == f(a)   , : 
      

        
        
        
      

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     ,  mreturn(a).get()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       , : 
      

        
        
        
      

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     , : 
      

        
        
        
      

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      ,     m.    ,        m. 
      

        
        
        
      

     
      

        
        
        
      

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           ,   ,   .      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
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         ,   ,          .       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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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Monad. , .

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ma, f f.



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, 5 11.



C++11 mreturn >>=. : n3721

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, , . 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(); }



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         ,   ,          .       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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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Monad. , .

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ma, f f.



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), Haskell C++.



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, 5 11.



C++11 mreturn >>=. : n3721

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, , . 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(); }



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       ,    5  11. 
      

        
        
        
      

     
      

        
        
        
      

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         ,   ,          .       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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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Monad. , .

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, 5 11.



C++11 mreturn >>=. : n3721

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, , . 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(); }



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       , : 
      

        
        
        
      

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       , : 
      

        
        
        
      

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     , : 
      

        
        
        
      

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       ,    5  11. 
      

        
        
        
      

     
      

        
        
        
      

      C++11      mreturn  >>=.      : n3721 
      

        
        
        
      

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         ,   ,          .       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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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Monad. , .

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



ma, f f.



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C++11 – std::async



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. : 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; }); }



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, . 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)



, :

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. - : 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

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make_ready_future



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>>=



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unwrap



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, , . 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(); }



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       ,    ,         ma,       f,         f. 
      

        
        
        
      

     
      

        
        
        
      

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         C++, : 
      

        
        
        
      

     (mreturn(a) >>= f) == f(a)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         ,   ,          .       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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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, , . 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(); }



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Monad. , .

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



ma, f f.



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, 5 11.



C++11 mreturn >>=. : n3721

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, , . 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(); }



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     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(); }); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         C++, : 
      

        
        
        
      

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       , : 
      

        
        
        
      

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        .    -     : 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
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         : 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(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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