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From: fischer@iesd.dk (Lars P. Fischer)
Newsgroups: comp.lang.c++
Subject: Re: Using OO Languages for Compilers/Interpreters
Message-ID: <1706@iesd.dk>
Date: 12 Apr 89 00:13:25 GMT
References: <16915@cup.portal.com> <3690007@wdl1.UUCP>
Sender: fischer@iesd.dk
Organization: Dept. of Computer Science, University of Aalborg
Lines: 41
In-reply-to: rme@wdl1.UUCP's message of 11 Apr 89 23:26:16 GMT


In article <3690007@wdl1.UUCP> rme@wdl1.UUCP (Richard M Emberson) writes:
>	A small (but by far the most important point) has been missed.
>	Simply to have  yacc or bison produce C++ code is not important,
>	but what is important is that their outputs are c++ classes.
>	This allows one to have multiple bnf grammers in the same
>	executable. (Try linking the output of two yacc grammers in the
>	same program - the yacc/bison drivers don't allow multiple
>	grammar tables).

From the BISON manual:

  Most programs that use Bison parse only one language and therefore
  contain only one Bison parser.  But what if you want to parse more
  than one language with the same program?  Here is what you must do:
  
     * Make each parser a pure parser (*note Pure Decl::.).  This gets
       rid of global variables such as `yylval' which would otherwise
       conflict between the various parsers, but it requires an
       alternate calling convention for `yylex' (*note Pure Calling::.).
  
     * In each grammar file, define `yyparse' as a macro, expanding
       into the name you want for that parser.  Put this definition in
       the C declarations section (*note C Declarations::.).  For
       example:
  
            %{
            #define yyparse parse_algol
  .....

The same could be done for (f)lex. 

This is not to say that a C++ parser object would be a bad thing, only
to point out that it can be done with ordinary function, and that
bison can do it, now.

/Lars
--
Copyright 1989 Lars Fischer; you can redistribute only if your recipients can.
Lars Fischer,  fischer@iesd.dk, {...}!mcvax!iesd!fischer
Any sufficiently advanced technology is indistinguishable from magic.
			-- Arthur C. Clarke