Re: [Boost-users] [proto] Unable to display_expr a spirit expression

Subject: Re: [Boost-users] [proto] Unable to display_expr a spirit expression
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2010-11-21 13:02:43

> I have a following program:
> 
> #include <boost/spirit/include/qi.hpp>
> #include <boost/spirit/include/phoenix_core.hpp>
> #include <boost/proto/core.hpp>
> 
> int main () {
>   // boost::proto::display_expr(boost::phoenix::arg_names::arg1);
> 
> boost::proto::display_expr(boost::spirit::int_[boost::phoenix::arg_names::
> arg1]);
> }
> 
> That works as expected:
> 
> subscript(
>     terminal(N5boost6spirit3tag4int_E)
>   , terminal(N5boost7phoenix5actorINS0_8argumentILi0EEEEE)
> )
> 
> When I include <boost/spirit/home/phoenix/operator.hpp> (as the last
> include), however, the output of the program changes to:
> 
> subscript(
>     terminal(N5boost6spirit3tag4int_E)
>   , terminal()
> 
> I am not sure if this is expected, unsupported, or a bug. Anyone?

That's expected as Proto does not know anything about Phoenix (V2). This
will be different with the new Phoenix V3 (in development), which is built
on top of Proto as well.

> Just to put this in context, I am trying to figure out how does spirit
> intercept phoenix expressions (e.g., in semantic actions) to wrap them in
> proto terminals. The infrastructure of spirit is rather complex, so if
> anyone can point me in the right direction, I would really appreciate it.

Spirit has special code to deal with Phoenix V2 function objects. For
instance, Phoenix semantic actions are handled here:
spirit/home/support/action_dispatch.hpp, line 41.

Regards Hartmut
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