Frans Englich wrote:
> On Tuesday 14 June 2005 11:36, Akim Demaille wrote:
>
>>>>>"Frans" == Frans Englich <[EMAIL PROTECTED]> writes:
>>
>> >
>> > I would prefer to do this at the Bison/Parser level because it is
>> > convenient: I have access to various information passed to the
>> > parse function,
>>
>>You can easily make them available to the scanner. And in fact, you
>>probably should, to have a clean, pure, interface bw the two.
>
>
> Ok, not fully following here, what you mean with "make them available to the
> scanner".
> [snip]
> Hm, then have error handling been placed in the scanner, which confuses me
> with respect to "You can easily make them available to the scanner. And in
> fact, you probably should, to have a clean, pure, interface bw the
> two."(assuming my interpretation is correct).
What Akim meant is that whatever information you pass to the parser
should also be passed down to the lexer.
Example:
=> in parserctx.h:
struct my_parse_context {
bool comments_allowed;
};
=> parser invocation:
...
struct my_parse_context pc;
fooparse(&pc);
...
=> in foo.y:
%{
...
#include "parserctx.h"
...
%}
%parse-param {my_parse_context* context}
%lex-param {my_parse_context* context}
...
=> in foo.l:
%{
...
#include "parserctx.h"
#define YY_DECL int yylex(my_parse_context* context)
...
%}
...
%%
{COMMENT} {
if (!context->comments_allowed) {
/* alternative: yyerror() and exit() if this is a fatal problem */
REJECT;
}
}
This way it becomes easy to pass information from the caller to parser &
lexer, and/or between lexer and parser. It also avoids using global
variables for such purposes, which keeps things thread-safe.
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