From johan@ccs.neu.edu Wed Oct  8 09:40:52 1997
Received: from carbon.ccs.neu.edu (carbon.ccs.neu.edu [129.10.114.110])
	by amber.ccs.neu.edu (8.8.6/8.7.3) with ESMTP id JAA09740; Wed, 8 Oct 1997 09:40:50 -0400 (EDT)
Received: (johan@localhost)
	by carbon.ccs.neu.edu (8.8.6/8.6.4) id JAA31312; Wed, 8 Oct 1997 09:40:48 -0400 (EDT)
Date: Wed, 8 Oct 1997 09:40:48 -0400 (EDT)
Message-Id: <199710081340.JAA31312@carbon.ccs.neu.edu>
From: Johan Ovlinger <johan@ccs.neu.edu>
To: lblando@gte.com
CC: dougo@ccs.neu.edu, lieber@ccs.neu.edu, dem@ccs.neu.edu
In-reply-to: <199710080804.EAA01353@rigel.ccs.neu.edu> (message from Doug
	Orleans on Wed, 8 Oct 1997 04:04:59 -0400 (EDT))
Subject: Re: primitive types in demjava
Status: R


 >    Field        ~ SubFieldName { "." SubFieldName } .
 >    SubFieldName = <name> Ident .

I like solutions where you don't have to muck about with supposedly
generated things like grammars. In this case, if you want to make an
Ident (or perhaps a String) of the all the SubFields after parsing,
use a so called derived edge. 

in the .cd file:

  SimpleField = <fields> Field <thestring> String. // Field as above.
  
in the .beh file:

  SimpleField {
    // this code will be called to return the <thestring> part. 
    get thestring (@ 
      // We'll print the fields to a stringstream
      StringWriter p = new StringWriter(); 
      // do the printing
      get_fields().universal_trv0(new PrintVisitor(new PrintWriter(p)));
      // extract the printed string	
      return p.toString();
    @)
  }


This'll do the trick, I hope. Every time you ask SimpleField for its
<thestring> part, it will be calculated from the subfields. I was a
bit worried that PrintVisitor would peint spaces between the "." and
the Idents, but the changes file says that it wont.

If you get_thestring() a lot, you might conscider caching the printed
string in SimpleField, but that is a performance conscideration, and
can be added transparently once everything is working.

Johan