I agree with Adrian — it would be nicer, in my opinion, to allow users to
handle syntax errors directly, rather than always going through the bison code
which formats syntax errors in a fixed way.
This seems like it might be not too hard to do: replace the code starting with
char const* yyformat = YY_NULLPTR;
switch (yycount)
{
#define YYCASE_(N, S) \
case N: \
yyformat = S; \
break
…
return yyres;
in yysyntax_error_ with a call like
my_yysyntax_error(yyarg, yycount);
where “my_yysyntax_error” is a user-defined function which does the work of
handling syntax error reporting.
In C++, we could be fancier: have two functions, one for a “pure” syntax error:
void my_yysyntax_error();
and one for syntax errors involving unexpected tokens:
void my_yysyntax_error(std::string unexpected_token,
std::vector<std::string> expected_tokens);
The call would be something like this:
if (yycount == 0) {
my_yysyntax_error();
} else {
my_yysyntax_error(yyarg[0], std::vector<std::string>{yyarg + 1, yyarg +
yycount});
}
Derek
> On Feb 6, 2019, at 11:23 AM, Adrian Vogelsgesang <avogelsges...@tableau.com>
> wrote:
>
> Hi Kevin, hi Akim,
>
> I can imagine cases where having a longer list of expected tokens might be
> useful.
> However, I wouldn’t like to have them in a string stitched together by bison,
> but instead I would like to have access to them in a std::vector<TokenId> or
> something similar.
> That way, I could do some post-processing of the expected token list (e.g.,
> expand the “variable_name” token to all variables which are currently in
> scope).
> The result could then be integrated with, e.g., a dropdown list for
> autocompletion pretty nicely :)
>
> Having programmatic access to the list of expected tokens would probably also
> solve Kevin’s request for reporting more than 5 tokens: he could just do it
> himself in his own code after getting the token list from Bison.
>
> Cheers,
> Adrian
>
> From: help-bison <help-bison-bounces+avogelsgesang=tableau....@gnu.org> on
> behalf of Akim Demaille <a...@lrde.epita.fr>
> Date: Wednesday, 6 February 2019 at 10:43
> To: Kevin Villela <ke...@villela.com>
> Cc: Bison Help <help-bison@gnu.org>
> Subject: Re: Forcing Bison's yacc.c to report more expected tokens on syntax
> error
>
> Hi Kevin,
>
>> Le 6 févr. 2019 à 03:01, Kevin Villela <ke...@villela.com> a écrit :
>>
>> Hi all, I saw that the yacc.c skeleton only supports reporting a maximum or
>> 5 expected tokens. The page
>> <https://www.gnu.org/software/bison/manual/html_node/LAC.html<https://www.gnu.org/software/bison/manual/html_node/LAC.html>>
>> on
>> Look-Ahead Correction states this is "because of internationalization
>> considerations". I was wondering if I would be able to contribute a
>> configuration option to increase this number arbitrarily, or even just up
>> to a higher number (e.g. 30) ?
>
> The thing is that it's unclear that it actually helps to report all the
> possibilities when there are too many.
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