Matt Wozniski wrote:
> On Thu, Mar 27, 2008 at 2:47 PM, Bram Moolenaar wrote: > > Xiaozhou Liu wrote: > > > > > During the development of the new regexp, one thing confuses me a lot: > > > ordered alternation. (e.g. given r.e. 'ab\|abc' and text 'abc', 'ab' > > > matched, not 'abc') > > > > > > I know that 100% compatibility is one of the project goals. So I try > > > to keep this feature > > > in the new regexp. But the problem is, ordered alternation is kind of > > > 'side effect' > > > of the original back track regexp matcher. AFAIK, It is very hard to > > > implement this > > > feature in the new, truly NFA matcher, if it is not impossible. We can > > resort > > > to the original regexp when we see '\|', but we don't solve the > > > problem perfectly. > > > > > > So does anyone really need this feature to be kept? If so, please do > > tell me. > > > For me, the removal of this 'feature' won't break anything. > > > > It is close to impossible to check that a change like this doesn't break > > existing scripts. And when something breaks, e.g. a syntax file, a > > normal user is very unlikely to be able to figure out what caused the > > problem. > > > > I stick to the opinion that the new regexp engine must work exactly > > like the existing one. Most things can be made to work that way. I > > also thought that this behavior of an alternate branch could be made to > > work in a DFA, with some effort. And otherwise we would have to fall > > back to the old engine when there is an alternate branch in the regexp. > > For what it's worth, I disagree strongly. This behavior is nothing > but a bug in the existing implementation - a documented bug, but a bug > nonetheless. I don't see why one would call this a bug. It's works this way intentionally. > In this particular case, I definitely think that we > should strive for compatibility with other regex engines, rather than > backwards compatibility with older vim versions. And, since this new > regex engine would likely not be introduced until vim 8.0, there is no > better time to break backwards compatibility. Since the old guarantee > that the leftmost alternation is matched first in fact makes regexes > work differently than in Perl, and in every POSIX implementation, and > make a DFA-based regex engine harder to write, I think we should > consider them as a historical fluke, and any syntax files that rely on > them to have been too cozy with the current engine. We should > re-write such syntax files, rather than keep a useful improvement out > of vim for their sake. No, backwards compatibility is more important. I don't want a newer version of Vim not being used because it breaks something that people can't figure out. A jump from 7.x to 8.x doesn't mean it's allowed to break things. Considering the recent OOXML fuzz I have lowered my appreciation for standards considerably. The Vim regexp engine isn't conforming to a standard and doesn't work like any other engine anyway, so I see no reason to make a detail work that way. It still will work quite different from other engines. -- hundred-and-one symptoms of being an internet addict: 189. You put your e-mail address in the upper left-hand corner of envelopes. /// Bram Moolenaar -- [EMAIL PROTECTED] -- http://www.Moolenaar.net \\\ /// sponsor Vim, vote for features -- http://www.Vim.org/sponsor/ \\\ \\\ download, build and distribute -- http://www.A-A-P.org /// \\\ help me help AIDS victims -- http://ICCF-Holland.org /// --~--~---------~--~----~------------~-------~--~----~ You received this message from the "vim_dev" maillist. For more information, visit http://www.vim.org/maillist.php -~----------~----~----~----~------~----~------~--~---
