Re: Parser base class (lalr1)

[Akim Demaille]

>>> "Jan" == Jan Nabbefeld <address@hidden> writes:

 > 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).

:(  Well, that's pretty much not elegant.  I'm also using lalr1.cc to
build an ast, but it looks like this:

exp.nonlvalue:
  "nil"
   { $$ = new ast::NilExp (@$); }
| "(" exps.0.2 ")"
   { $$ = new ast::SeqExp (@$, $2); }
| "(" error ")"
   { $$ = new ast::SeqExp (@$, new ast::exps_type); }
| lvalue ":=" exp
   { $$ = new ast::AssignExp (@$, $1, $3); }
| "if" exp "then" exp
   { $$ = new ast::IfExp (@$, $2, $4); }
| "if" exp "then" exp "else" exp
   { $$ = new ast::IfExp (@$, $2, $4, $6); }

etc. etc.

A simple `using namespace ast' removes the ast:: if needed.


 > Also the initial AST node would be a usefull class attribute in
 > parser.

Sorry, I don't quite understand what you mean with `the initial ast
node'.

 > 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 have not understood what mandates that these NNew etc. be members of
the parser.  They can be non member functions used by the parser, no?

Have a look at examples/calc++ in the Bison distro: that's what I have
in mind for the "right" use.