[plt-scheme] abstracting parsers

Is this a problem of macros in general?

I noticed that I've started writing too many rules like this one:

(hex [(A) $1]
     [(B) $1]
     ...
     [(ZERO) $1]
     [(ONE) $1]
     ...)

and would rather write:

(same-as hex
         ZERO ONE TWO THREE FOUR FIVE SIX SEVEN EIGHT NINE A B C D E F)

but can't define a same-as macro here.. I need to write some parser++
syntax that includes same-as.

Or do I (hopefully) misunderstand the macro system?

Daniel



On Fri, 7 May 2004, Scott Owens wrote:

>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> 
> That is not directly possible.  The same grammar can define multiple parsers 
> by using multiple start non-terminals, but grammars cannot use non-terminals 
> from other grammars.  You could define your own syntactic abstraction for 
> parsers that expands into the `parser' form.
> 
> -Scott
> 
> On Friday 07 May 2004 04:50 pm, Daniel Silva wrote:
> >   For list-related administrative tasks:
> >   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> >
> > I'm working on a message parser for some protocol defined in an RFC.
> > Parts of those messages (some non-terminals) are defined in other RFCs.
> > It would be nice to be able to refer to non-terminals from other grammars.
> > Is this possible?
> >
> > For example, something like:
> >
> > ;; RFC 2396 defines Uniform Resource Identifiers (URIs)
> >
> > (require (prefix rfc2396: (lib "RFC2396.ss"
> >                                "IETF" "RFCs")))
> >
> > (parser
> >   (grammar
> >      ...
> >      (Request-Line [(Method SP Request-URI SP HTTP-Version CRLF)
> >                     (make-request-line $1 $3 $5)])
> >
> >      (Request-URI [(ASTERISK) $1]
> >                   [(rfc2396:absolute-uri) $1]
> >                   [(rfc2396:abs_path) $1]
> >                   [(rfc2396:authority) $1])
> >
> >      ...))
>