Re: [boost] Boost.Spirit comments and stuff

From: Joel de Guzman (joel_at_[hidden])
Date: 2004-03-20 18:31:01

Reece Dunn wrote:

> I have been learning Boost.Spirit over the past few days and here are a 
> few queries:
> 
> [1] Is it possible to process a token stream rather than a character 
> stream? If so, are there any examples? The reason I am asking is...

Yes. See Hartmut Kaiser's Wave CPP preprocessor.

> [2] Is it possible to cascade spirit grammars, e.g.
> 
>   wave.parse() >> cpp.parse(); // hypothetical

Yes.

> where the output of the wave grammar feeds the token stream of the cpp 
> grammar. I am not propsing that the above is how this would be expressed.
> 
> [3] Is it possible to combine the file_iterator with the 
> position_iterator to provide error reporting on that?

Yes.

> [4] I am now making use of boost::spirit::sub_grammar from 
> libs/spirit/doc/techniques.html. One thing I get from this is that the 
> typedef for the grammar type can be very difficult to read, especially 
> for non-trivial grammars! I have started writing a set of type helpers 
> to simplify the process:
> 
>   namespace boost { namespace spirit
>   {
>      template< typename T1, typename T2, typename T3 >
>      struct alternative3_t
>      {
>         typedef alternative< alternative< T1, T2 >, T3 > type;
>      };
> 
>      template< typename T1, typename T2, typename T3 >
>      struct sequence3_t
>      {
>         typedef sequence< sequence< T1, T2 >, T3 > type;
>      };
> 
>      // confix_type = T1 >> *( CompositeT - T2 ) >> T2
> 
>      template< typename CompositeT, typename T1 = strlit< const char * 
>  >, typename T2 = T1 >
>      struct confix_t
>      {
>         typedef typename sequence3_t
>         <
>            T1,
>            kleene_star< difference< CompositeT, T2 > >,
>            T2
>         >::type type;
>      };
> 
>      template< typename T2 = strlit< const char * >, typename T1 = 
> strlit< const char * > >
>      struct comment_t
>      {
>         typedef typename confix_t< anychar_parser, T1, T2 >::type type;
>      };
> 
>      typedef comment_t< chlit< char > >::type line_comment;
>      typedef comment_t<>::type range_comment;
>   }}
> 
> using these, the typedef for the skip_grammar example becomes:
> 
>   typedef typename boost::spirit::alternative3_t
>   <
>      boost::spirit::space_parser,
>      boost::spirit::line_comment,
>      boost::spirit::range_comment
>   >::type start_t;
> 
> If there is interest, I shall create a proper submission for them.

Oh, very cool! That would be very nifty indeed.

Cheers,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net