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//[ RGB
///////////////////////////////////////////////////////////////////////////////
// Copyright 2008 Eric Niebler. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// This is a simple example of doing arbitrary type manipulations with proto
// transforms. It takes some expression involving primary colors and combines
// the colors according to arbitrary rules. It is a port of the RGB example
// from PETE (http://www.codesourcery.com/pooma/download.html).
#include <iostream>
#include <boost/proto/core.hpp>
#include <boost/proto/transform.hpp>
namespace proto = boost::proto;
struct RedTag
{
friend std::ostream &operator <<(std::ostream &sout, RedTag)
{
return sout << "This expression is red.";
}
};
struct BlueTag
{
friend std::ostream &operator <<(std::ostream &sout, BlueTag)
{
return sout << "This expression is blue.";
}
};
struct GreenTag
{
friend std::ostream &operator <<(std::ostream &sout, GreenTag)
{
return sout << "This expression is green.";
}
};
typedef proto::terminal<RedTag>::type RedT;
typedef proto::terminal<BlueTag>::type BlueT;
typedef proto::terminal<GreenTag>::type GreenT;
struct Red;
struct Blue;
struct Green;
///////////////////////////////////////////////////////////////////////////////
// A transform that produces new colors according to some arbitrary rules:
// red & green give blue, red & blue give green, blue and green give red.
struct Red
: proto::or_<
proto::plus<Green, Blue>
, proto::plus<Blue, Green>
, proto::plus<Red, Red>
, proto::terminal<RedTag>
>
{};
struct Green
: proto::or_<
proto::plus<Red, Blue>
, proto::plus<Blue, Red>
, proto::plus<Green, Green>
, proto::terminal<GreenTag>
>
{};
struct Blue
: proto::or_<
proto::plus<Red, Green>
, proto::plus<Green, Red>
, proto::plus<Blue, Blue>
, proto::terminal<BlueTag>
>
{};
struct RGB
: proto::or_<
proto::when< Red, RedTag() >
, proto::when< Blue, BlueTag() >
, proto::when< Green, GreenTag() >
>
{};
template<typename Expr>
void printColor(Expr const & expr)
{
int i = 0; // dummy state and data parameter, not used
std::cout << RGB()(expr, i, i) << std::endl;
}
int main()
{
printColor(RedT() + GreenT());
printColor(RedT() + GreenT() + BlueT());
printColor(RedT() + (GreenT() + BlueT()));
return 0;
}
//]
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