Re: push parser

[Paul Eggert]

Bob Rossi <address@hidden> writes:

> --- yacc.c    2006-10-10 14:06:22.000000000 -0400
> +++ push.c    2006-10-10 10:49:23.000000000 -0400
>     @@ -152,6 +152,9 @@
>      m4_if(b4_prefix, [yy], [],
>      [/* Substitute the variable and function names.  */
>      #define yyparse b4_prefix[]parse
>     +#define yypushparse b4_prefix[]pushparse
>     +#define yypvarsinit b4_prefix[]pvarsinit
>     +#define yypvars b4_prefix[]pvars
>      #define yylex   b4_prefix[]lex
>      #define yyerror b4_prefix[]error
>      #define yylval  b4_prefix[]lval
>
> These are 3 new symbols that get defined depending on the prefix.

Are these symbols needed if it's not a push parser?  If not, perhaps
they should be protected with b4_push_if.  Similarly for any other
changes needed only for the push parser.

>     @@ -1009,6 +1121,7 @@
>      #if YYERROR_VERBOSE
>        /* Buffer for error messages, and its allocated size.  */
>        char yymsgbuf[128];
>     +  char *yymsgbuf_ptr = yymsgbuf;
>        char *yymsg = yymsgbuf;
>        YYSIZE_T yymsg_alloc = sizeof yymsgbuf;
>      #endif
>
> yymsgbuf_ptr is added. This is probably the first confusing difference
> between the 2 patches. You will see this solution used in at least 2 
> other places. Essentially, yacc.c was using yymsgbuf in yyparse. So,
> the yypvars structure also has a 'char yymsgbuf[128];'. However, when
> the pull parse is being used, it wants yymsgbuf to refer to the local 
> stack variable, and when the push parser is being used, it wants 
> yymsgbuf to refer to the variable in the yypvars structure.

I don't see why these changes are needed.  Why can't the push parser
use a local variable, just as the pull parser does?  The buffer in
question is needed only for the call to yysyntax_error.  Its storage
does not need to survive until the next call to yypushparse.

>     @@ -1023,6 +1136,7 @@
>      
>        /* The state stack.  */
>        yytype_int16 yyssa[YYINITDEPTH];
>     +  yytype_int16 *yyssa_ptr = yyssa;
>        yytype_int16 *yyss = yyssa;
>        yytype_int16 *yyssp;
>
> Same idea as above here.
>  
>     @@ -1037,7 +1151,9 @@
>        YYLTYPE *yyls = yylsa;
>        YYLTYPE *yylsp;
>        /* The locations where the error started and ended.  */
>     -  YYLTYPE yyerror_range[2];]])[
>     +  YYLTYPE yyerror_range[2];
>     +  YYLTYPE *yyerror_range_ptr = yyerror_range;
>     +  ]])[
>
> Again, same idea.

I guess this is different from yymsgbuf_ptr, since this storage does
need to survive from one call to the next.  But I don't see why the
pointers are needed here, either.  If it's always the case that
yyssa_ptr == pv->yyssa then you can simply use pv->yyssa rather than
maintaining a separate pointer.  Likewise for yyerror_range_ptr.