Re: [Boost-users] [phoenix][lambda] lambda to phoenix translation: get sig (signature) from actor

Subject: Re: [Boost-users] [phoenix][lambda] lambda to phoenix translation: get sig (signature) from actor
From: alfC (alfredo.correa_at_[hidden])
Date: 2010-06-02 05:03:30

On May 31, 3:07 am, Joel de Guzman <j..._at_[hidden]> wrote:
> What are the args to LambdaExp?

ok, I think I simplified the code as much as possible to its bare
bones, here it is a compilable example of what I need.
as you see first there is a lambda version which is concise and works,
then follows the phoenix attempt.
I have and expression template _1 + 1. or arg1 + 1. and I am trying to
compose it with two free functions (sq and div2).
Take _1 + 1. or arg1 + 1. as black box (this is an example of what the
subexpression that the pattern matching recognizes in the full
example).

The precise question is what is the phoenix translation of the lambda
"bind(&div2, (_1+1.)(bind(&sq, _1) ) )" ?
[ _1+1. is just an example, in the real code is some argument passed
and can be any expression, in other words "(_1+1.)" must remain there,
so (bind(&div2, (bind(&sq,arg1) ) + 1. ) is not the answer I am
looking for].

the full minimal example is below:

#include<boost/function.hpp>
#include<boost/spirit/home/phoenix.hpp>
#include<boost/lambda/lambda.hpp>
#include<boost/lambda/bind.hpp>

double sq(double x){return x*x;}
double div2(double x){return x/2.;}
using namespace std;
int main(){
        {// first with lambda
                using namespace boost::lambda;
                double const dos = 2.;
                boost::function<double(double)> f( bind(&div2, (_1+1.)(bind(&sq,
_1) ) ) );
                cout<< f(dos) << endl;  // returns 2.5
        }
        {// second with phoenix
                using namespace boost::phoenix;
                using namespace boost::phoenix::arg_names;
                double const dos = 2.;
        //	boost::function<double(double)> f( (bind(&div2, (arg1+1.)
(bind(&sq,arg1) ) ) )); //doesn't work, what goes here??
        //	cout<< f(dos) << endl; // should return 2.5
        }
  return 0;
};

I tried all sorts of things, I am starting to think that Phoenix is
not designed for this (although it is supposed to be a generalization
of BLL.)

Thank you,
Alfredo