Re: [Boost-users] [Proto]: How to use complex grammars in a domain/extension

Subject: Re: [Boost-users] [Proto]: How to use complex grammars in a domain/extension
From: joel falcou (joel.falcou_at_[hidden])
Date: 2010-09-20 14:04:50

On 20/09/10 19:59, Roland Bock wrote:
> Hi,
>
> I am trying to create a DSEL with Boost.Proto, which (among other 
> things) should allow expressions like
>
> i == j + 3 && t != "foo"
>
> and want to prevent disallowed operators to be generated by Proto.
>
> Please consider the code below.
>
> // 
> -----------------------------------------------------------------------
> #include<boost/proto/proto.hpp>
>
> using namespace boost;
>
> typedef proto::terminal<int>::type terminal;
>
> struct addition:
>    proto::or_
> <
>       terminal,
>       proto::plus<addition, addition>
> >
> {};
>
> struct equation:
>    proto::equal_to<addition, addition>
> {};
>
> struct condition:
>    proto::or_
> <
>       equation,
>       proto::logical_and<equation, equation>
> >
> {};
>
> In my_domain, I can replace condition by addition, which allows i + i, 
> but then the == operator is still missing (and the &&, too, probably).

i+i doesn't match your grammar at all.
an equation is addition == addition which is not matchable by i+i
if equation was:

struct equation:
   proto::or_< addition,   proto::equal_to<addition, addition> >
{};

then it'll work.