mirror of
https://git.savannah.gnu.org/git/bison.git
synced 2026-03-09 04:13:03 +00:00
d9a9b054ae
The user gives yyexpected_tokens a limit: the max number of tokens she
wants to hear about. That's because an error message that reports a
bazillion of possible tokens is useless.
In that case yyexpected_tokens returned 0, so the user would not know
if there are too many expected tokens or none (yes, that's possible).
There are several ways to tell the user in which situation she's in:
- return some E2MANY, a negative value. Then it makes the pattern
int argsize = yypcontext_expected_tokens (ctx, arg, ARGS_MAX);
if (argsize < 0)
return argsize;
no longer valid, as for E2MANY (i) the user must generate the error
message anyway, and (ii) she should not return E2MANY
- return ARGS_MAX + 1. Then it makes it dangerous for the user, as
she has to iterate update `min (ARGS_MAX, argsize)`.
Returning 0 is definitely simpler and safer for the user, as it tells
her "this is not an error, just generate your message without a list
of expecting tokens". So let's still return 0, but set arg[0] to the
empty token when the list is really empty.
* data/skeletons/glr.c, data/skeletons/lalr1.cc, data/skeletons/lalr1.java
* data/skeletons/yacc.c (yyexpected_tokens): Put the empty symbol
first if there are no possible tokens at all.
* examples/c/bistromathic/parse.y: Demonstrate how to use that.
This directory contains examples of Bison grammar files, sorted per language.
Several of them come from the documentation, which should be installed together with Bison. The URLs are provided for convenience.
These examples come with a README and a Makefile. Not only can they be used to toy with Bison, they can also be starting points for your own grammars.
Please, be sure to read the C examples before looking at the other languages, as these examples are simpler.