Re: [boost] Phoenix and lambda...

From: joel de guzman (djowel_at_[hidden])
Date: 2002-03-21 21:37:15

Hi,

How about this code:

struct square_ {
  template <typename ArgX>
  struct result { typedef ArgX type; };

  template <typename ArgX>
  ArgX operator()(ArgX arg1) {
    return arg1 * arg1;
  }
};

function<square_> square;

int
main()
{
    std::cout << "Square of " << 5 << " is " << square(5)() << std::endl;
    std::cout << "Double Square of " << 5 << " is " << square(square(5))() << std::endl;
}

will print out:

Square of 5 is 25
Double Square of 5 is 625

Am I missing something? If so, pardon my for being slow. 

Cheers,
--Joel

----- Original Message ----- 
From: "Joel Young" :

> 
> So phoenix looks really cool!
> 
> I was playing around with Phoenix trying to get the following:
> 
>         -  \         \
> double  -  /\  f .   /\   x.  f(f x)
>         - /  \      /  \
> 
> 
> but the best I was able to figure out is:
> 
>  
>         -  \          
> double  -  /\  (f, x).f(f x)
>         - /  \        
> 
> 
> where double = fof in below code snippet:
> 
> Any suggestions?
> 
> // cut
> struct fof_ {
>   template <typename ArgF, typename ArgX>
>   struct result { typedef ArgX type; };
> 
>   template <typename ArgF, typename ArgX>
>   ArgX operator()(ArgF arg1, ArgX arg2) {
>     return arg1(arg1(arg2))();
>   }
> };
> 
> // fof equiv lambda(f,x).f(f x)
> function<fof_> fof;
> 
> struct square_ {
>   template <typename ArgX>
>   struct result { typedef ArgX type; };
> 
>   template <typename ArgX>
>   ArgX operator()(ArgX arg1) {
>     return arg1 * arg1;
>   }
> };
> 
> function<square_> square;
> 
> int
> main()
> {
>     std::cout << "Square of " << 5 << " is " << square(5)() << std::endl;
>     std::cout << "Double Square of " << 5 << " is " << fof(square,5)() << std::endl;
> }
> // cut
> 
> 
> Joel
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