BoostPhoenix3: miniphoenix2.cpp

#include <algorithm>
#include <boost/mpl/if.hpp>
#include <boost/fusion/container/vector.hpp>
#include <boost/proto/proto.hpp>

namespace boost
{
namespace phoenix
{
using namespace proto;

//////////////////////////////
// phoenix expression wrapper
template<class Expr>
struct actor;

//////////////////////////////
struct phoenix_domain
  : domain<pod_generator<actor> >
{};

//////////////////////////////
// phoenix grammar and expression evaluator
struct eval
  : switch_<struct eval_cases>
{};

//////////////////////////////
struct eval_cases
{
    template<class Tag>
    struct case_
      : _default<eval>
    {};
};

//////////////////////////////
template<class Sig>
struct actor_result;

#define BOOST_PROTO_LOCAL_MACRO(N, class_A, A, A_const_ref_a, a)\
template<class Actor, class_A(N)>                               \
struct actor_result<Actor(A(N))>                                \
  : boost::result_of<eval(Actor&, fusion::vector<A(N)> &)>      \
{};

#define BOOST_PROTO_LOCAL_A BOOST_PROTO_A
#include BOOST_PROTO_LOCAL_ITERATE()

//////////////////////////////
template<class Expr>
struct actor
{
#define BOOST_PHOENIX_ACTOR(Base, Derived, Domain)                      \
    BOOST_PROTO_BASIC_EXTENDS(Base, Derived, Domain)                    \
    BOOST_PROTO_EXTENDS_ASSIGN()                                        \
    BOOST_PROTO_EXTENDS_SUBSCRIPT()                                     \
                                                                        \
    template<class Sig>                                                 \
    struct result : actor_result<Sig>                                   \
    {};                                                                 \
                                                                        \
    typedef Derived actor_type;                                         \
    BOOST_PROTO_REPEAT(BOOST_PHOENIX_INVOKE)                            \
    /**/

#define BOOST_PHOENIX_INVOKE(N, class_A, A_const_ref, A_const_ref_a, a) \
    template<class_A(N)>                                                \
    typename boost::result_of<actor_type(A_const_ref(N))>::type         \
    operator()(A_const_ref_a(N)) const                                  \
    {                                                                   \
        BOOST_PROTO_ASSERT_MATCHES(*this, eval);                        \
        fusion::vector<A_const_ref(N)> args(a(N));                      \
        return eval()(*this, args);                                     \
    }                                                                   \
    /**/

    BOOST_PHOENIX_ACTOR(Expr, actor<Expr>, phoenix_domain)
};

//////////////////////////////
// Begin implementation of _1, _2, _3 argument placeholders
//
struct arg_tag {};

//////////////////////////////
struct at : callable
{
    template<class Sig>
    struct result;

    template<class This, class Cont, class N>
    struct result<This(Cont &, N &)>
      : fusion::result_of::at<Cont, N>
    {};

    template<class Cont, class N>
    typename fusion::result_of::at<Cont, N>::type
    operator ()(Cont &cont, N) const
    {
        return fusion::at<N>(cont);
    }
};

//////////////////////////////
actor<nullary_expr<arg_tag, mpl::int_<0> >::type> const _1 = {{{}}};
actor<nullary_expr<arg_tag, mpl::int_<1> >::type> const _2 = {{{}}};
actor<nullary_expr<arg_tag, mpl::int_<2> >::type> const _3 = {{{}}};

//////////////////////////////
template<>
struct eval_cases::case_<arg_tag>
  : when<nullary_expr<arg_tag, _>, at(_state, _value)>
{};

//////////////////////////////
// Begin implementation of if_/else_ here
//
struct if_tag {};
struct else_tag {};
struct if_else_tag {};

template<class Expr>
struct if_else_actor;

// if_(x)[y]
struct if_stmt
  : subscript<function<terminal<if_tag>, eval>, eval>
{};

// if_(x)[y].else_[z]
struct if_else_stmt
  : subscript<
        member<unary_expr<if_tag, if_stmt>, terminal<else_tag> >
      , eval
    >
{};

typedef functional::make_expr<if_tag>       make_if;
typedef functional::make_expr<if_else_tag>  make_if_else;
typedef pod_generator<if_else_actor>        make_if_else_actor;

//////////////////////////////
struct if_else_generator
  : or_<
        // if_(this)[that]
        when<
            if_stmt
            // wrap in if_else_actor and unary if_tag expr
          , make_if_else_actor(make_if(_byval(_)))
        >
        // if_(this)[that].else_[other]
      , when<
            if_else_stmt
            // wrap in if_else_actor and unary if_else_tag expr
          , make_if_else_actor(make_if_else(_byval(_)))
        >
      , otherwise<
            make_if_else_actor(_)
        >
    >
{};

//////////////////////////////
struct if_else_domain
  : domain<if_else_generator>
{};

//////////////////////////////
struct complete_if_else_stmt
  : or_<
        unary_expr<if_tag, if_stmt>
      , unary_expr<if_else_tag, if_else_stmt>
    >
{};

//////////////////////////////
template<class Expr>
struct if_else_actor
{
    typedef typename
        mpl::if_<matches<Expr, complete_if_else_stmt>, phoenix_domain, if_else_domain>::type
    domain_;

    BOOST_PHOENIX_ACTOR(Expr, if_else_actor<Expr>, domain_)

    // Declare a member named else_ that is a
    // terminal<if_else_tag> in if_else_domain.
    BOOST_PROTO_EXTENDS_MEMBERS_WITH_DOMAIN(
        ((else_tag,   else_))
      , if_else_domain
    )
};

// Function for evaluating lambdas like: if_(foo)[bar]
struct if_eval : callable
{
    typedef void result_type;

    template<class I, class T, class S>
    void operator()(I const & i, T const & t, S & s) const
    {
        if( eval()(i, s) )
            eval()(t, s);
    }
};

// Function for evaluating lambdas like: if_(foo)[bar].else_[baz]
struct if_else_eval : callable
{
    typedef void result_type;

    template<class I, class T, class E, class S>
    void operator()(I const & i, T const & t, E const & e, S & s) const
    {
        if( eval()(i, s) )
            eval()(t, s);
        else
            eval()(e, s);
    }
};

//////////////////////////////
typedef functional::make_expr<tag::function, if_else_domain> make_fun;

template<class E>
typename boost::result_of<make_fun(if_tag, E const &)>::type const
if_(E const & e)
{
    return make_fun()(if_tag(), ref(e));
}

//////////////////////////////
// This tells Proto how to evaluate if_(x)[y] statements with if_eval
template<>
struct eval_cases::case_<if_tag>
  : when<
        unary_expr<if_tag, if_stmt>
      , if_eval(_right(_left(_left)), _right(_left), _state)
    >
{};

//////////////////////////////
// This tells Proto how to evaluate if(x)[y].else_[z] statements with if_else_eval
template<>
struct eval_cases::case_<if_else_tag>
  : when<
        unary_expr<if_else_tag, if_else_stmt>
      , if_else_eval(
            _right(_left(_left(_left(_left(_left)))))
          , _right(_left(_left(_left(_left))))
          , _right(_left)
          , _state
        )
    >
{};

} // namespace phoenix
} // namespace boost

#include <iostream>
using namespace boost;
using namespace phoenix;

int main()
{
    int j = (_1 + _2)(1, 2);
    std::cout << j << "\n";

    j = (_2 * 2)(1, 2);
    std::cout << j << "\n";

    phoenix::if_(_1)[std::cout << _2 << "\n"] + _1;

    phoenix::if_(_1)[std::cout << _2 << "\n"](1,2,3);
    phoenix::if_(_1)[std::cout << _2 << "\n"].else_[std::cout << _3 << "\n"](1,2,3);
    phoenix::if_(_1)[std::cout << _2 << "\n"].else_[std::cout << _3 << "\n"](0,2,3);

    int x[] = { 1, 2, 3, 4 };
    int y[] = { 2, 4, 6, 8 };
    int z[4];

    // Use a Phoenix lambda with std algorithms
    std::transform( x, x + 4, y, z, _1 * _2 );
}