Functional Programming in C++ [closed]

Question

Can someone guide me how do functional programming in C++? Is there some good online material that I can refer?

Please note that I know about the library FC++. I want to know how to do that with C++ standard library alone.

Thanks.

Answer 1

You can accomplish a surprising amount of "functional programming" style with modern C++. In fact, the language has been trending in that direction since its' standardization.

The standard library contains algorithms analogous to map, reduce, etc (for_each, transform, adjacent_sum...). The next revision, C++0x, contains many features designed to let programmers work with these in a more functional style (lambda expressions, etc.).

Look into the various Boost libraries for more fun. Just to illustrate that standard C++ contains plenty of functional goodness, here's a factorial function in continuation-passing style in standard C++.

#include <iostream>  // abstract base class for a continuation functor struct continuation {     virtual void operator() (unsigned) const = 0; };  // accumulating continuation functor struct accum_cont: public continuation {     private:         unsigned accumulator_;         const continuation &enclosing_;     public:         accum_cont(unsigned accumulator, const continuation &enclosing)             : accumulator_(accumulator), enclosing_(enclosing) {};          virtual void operator() (unsigned n) const {             enclosing_(accumulator_ * n);         }; };  void fact_cps (unsigned n, const continuation &c) {     if (n == 0)         c(1);     else         fact_cps(n - 1, accum_cont(n, c)); }  int main () {     // continuation which displays its' argument when called     struct disp_cont: public continuation {         virtual void operator() (unsigned n) const {             std::cout << n << std::endl;         };     } dc;      // continuation which multiplies its' argument by 2     // and displays it when called     struct mult_cont: public continuation {         virtual void operator() (unsigned n) const {             std::cout << n * 2 << std::endl;         };     } mc;      fact_cps(4, dc); // prints 24     fact_cps(5, mc); // prints 240      return 0; } 

Ok, I lied a little bit. It's a factorial functor. After all, closures are a poor man's objects... and vice versa. Most of the functional techniques used in C++ rely on the use of functors (i.e. function objects)---you'll see this extensively in the STL.