Re: Parser base class (lalr1)

[Jan Nabbefeld]

Hello,
Akim Demaille wrote:
> This [1] was not defined.

Sorry, here it comes again:
http://lists.gnu.org/archive/html/help-bison/2002-07/msg00047.html

>  > about the possibelity off defining a base class for the generated
>  > yy::parser in lalr1 skeleton. Further I noticed that this was
>  > removed from the lalr1 skeleton on December 2004.
> That is right, it seemed to cause more problems than provide
> solutions.  Do you have a concrete example where this would be useful?
> Would you also want to derive from it?

A piece of the parser file:
-8<-----
/* ... */
cd_list: /* empty */ {$$=0;}
        | cd_list cd { $$ = NRec(token, _CD_LIST, $1, $2, _CD); }
;

cd: opt_final class_definition ';'
  { $$ = NLift(token, _CD, $1, $2, _OPT_FINAL, _CLASS_DEFINITION); }
;

opt_final: /* empty */  {$$=0;}
        | FINAL { $$=NNew(token); $$->type=FINAL; }
;
/* ... */
-8<-----

I would love to have NNew(), NLift() and NRec() as parser methods (for 
building AST). Also the initial AST node would be a usefull class 
attribute in parser. Unfortunately I'm bound by the BNF rules shown 
above. So changes can only be made on the surrounding code.

Parent class of generated yy::parser:
-8<-----
class parserBase:
{
  public:
    parserBase(const Param& p) :
      lexer (new FlexLexer ()),
      token (new TokenType ()),
      ast (0)
      {}
    tree * ast;
    tree * NNew(tokenType *);
    ...
}
-8<-----

This works well with Bison <= 1.875e (OK, skeleton changes between the 
1.875x releases broke the code again but it worked in general). I know 
lalr1.cc skeleton is experimantal and not supported so I don't complain 
about that. Would be nice to have the possibility again without 
customize the skeleton.

I hope this makes the situation a little bit clearer.
Thanks,
Jan Nabbefeld