I made an implementation of .NET-style variable length lookbehinds. It's not in a JS engine, but it's in a very simple (and very slow) ES5-compatible regexp engine that is used in the tiny Dart implementation named Fletch.
No unicode issues arise since this engine does not support /u, but I don't expect any issues since it's not trying to second-guess the length of the string matched by an expression. Needs a lot more tests, but it seems to work OK and was surprisingly simple to do. Basically: * All steps in the input string are reversed, so if you would step forwards you step backwards. * Check for start of string instead of end of string. * Test against the character to the left of the cursor instead of to the right. * The parts of the Alternative (see the regexp grammar in the standard) are code-generated in reverse order. Code is here: https://codereview.chromium.org/1398033002/ On Wed, Oct 7, 2015 at 9:08 PM, Brian Terlson <[email protected]> wrote: > Sebastian, > > > > You can follow the tc39/ecma262 github repository for updates on > proposals. It also contains information about our process. > > > > *From:* Sebastian Zartner [mailto:[email protected]] > *Sent:* Monday, October 5, 2015 10:56 PM > *To:* Nozomu Katō <[email protected]> > *Cc:* Brian Terlson <[email protected]>; es-discuss Mozilla < > [email protected]>; Gorkem Yakin <[email protected]> > *Subject:* Re: Look-behind proposal in trouble > > > > Hi together, > > Brian, where can people get the information about the reasons of such > decisions (besides asking) and more generally about the processes behind > the ES development? > > I was following Nozomu's proposal[1] closely, though to me it looked like > the progress on this just died out. > > Non-the-less, great to hear that new champions could be found! > > > > Sebastian > > [1] https://mail.mozilla.org/pipermail/es-discuss/2015-May/042910.html > <https://na01.safelinks.protection.outlook.com/?url=https%3a%2f%2fmail.mozilla.org%2fpipermail%2fes-discuss%2f2015-May%2f042910.html&data=01%7c01%7cBrian.Terlson%40microsoft.com%7c9a8b71c0d5aa44e2cc5608d2ce12eaa6%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=L42fz4DoEDGTJTX0Tkz4OvQU03XONPnxMcjsH5zOT1Q%3d> > > > > On 5 October 2015 at 23:42, Nozomu Katō <[email protected]> wrote: > > Hello Brian, > > I thank you very much indeed for your email and bringing really good > news! I thought that my proposal might not be able to move forward > anymore. > > I am also thankful that you searched for a new champion and Gorkem > undertakes this proposal! > > Regards, > Nozomu > > > Brian Terlson wrote on Mon, 5 Oct 2015, at 20:29:18 +0000: > > Hi Nozomu, > > > > Brendan has indeed discovered he doesn't have time to champion the > > proposal through TC39, so I removed it while I searched for a new > > champion. Good news on that front - I have found one! Gorkem Yakin > > works on the Chakra team and is available to help move this proposal > > forward. I will also help out where I can. I've added the proposal > > back to the stage 0 list! > > > > Thanks, > > Brian > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > <https://na01.safelinks.protection.outlook.com/?url=https%3a%2f%2fmail.mozilla.org%2flistinfo%2fes-discuss&data=01%7c01%7cBrian.Terlson%40microsoft.com%7c9a8b71c0d5aa44e2cc5608d2ce12eaa6%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=CkApvLPKtBkJEMHhTi7fnCpbZXpZi1R3vvJaca0kxDY%3d> > > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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