Tom, > Le 23 mai 2019 à 06:00, Tom Lane <t...@sss.pgh.pa.us> a écrit : > > Robert Haas <robertmh...@gmail.com> writes: >> Another thing is that it would be nice to have a better way of >> resolving conflicts than attaching precedence declarations. Some >> problems can't be solved that way at all, and others can only be >> solved that way at the risk of unforeseen side effects. > > Yeah, we've definitely found that resolving shift/reduce conflicts via > precedence declarations has more potential for surprising side-effects > than one would think.
That's why in recent versions of Bison we also provide a means to pure %expect directives on the rules themselves, to be more precise about what happens. > It feels to me that there's something basically > wrong with that concept, or at least wrong with the way we've used it. I'm trying to find means to scope the prec/assoc directives, because they are too powerful, and that's dangerous. This is also why I try to remove the useless ones. Some people don't trust assoc/prec directives at all and use only unambiguous grammars. But this can be very verbose... I agree something is not so cool about these directives. GLR parsers have a clear concept of in-between-rules precedence (%dprec). Something similar for LR (hence fully static) would be nice, but it remains to be invented.
