I think this is right, we need help and are open to it from someone who
can lift the weight. Waldemar may be able to help, I'm not sure how much
(but he wrote the ES3 regexp spec, so at least as reviewer he is a key
part of the solution).
Sebastian, if you have time to help, that would be tremendous.
/be
Jason Orendorff <mailto:jason.orendo...@gmail.com>
October 2, 2013 5:15 AM
Sebastian,
Here is how I interpret Waldemar's post:
On Mon, Sep 30, 2013 at 5:55 PM, Waldemar Horwat<walde...@google.com> wrote:
No one has yet submitted a well-defined proposal for lookbehinds on the
table. Lookbehinds are difficult to translate into the language used by the
spec [...]
This is the real problem. No one has taken on the work. It's a fair
amount of very technical work.
[...] and get quite fuzzy when the order of evaluation of parts of the regexp
matters, which is what happens if capturing parentheses are involved. Where
do you start looking for the lookbehind? Shortest first, longest first, or
reverse string match? Greedy or not? Backtrack into capturing results?
Sebastian, as you pointed out, these technical points have all been
addressed one way or another in practice. My guess is that TC39
*would* accept some commonly-implemented lookbehind behavior, if
someone put up the work. I could be wrong.
-j
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Waldemar Horwat <mailto:walde...@google.com>
September 30, 2013 3:55 PM
No one has yet submitted a well-defined proposal for lookbehinds on
the table. Lookbehinds are difficult to translate into the language
used by the spec and get quite fuzzy when the order of evaluation of
parts of the regexp matters, which is what happens if capturing
parentheses are involved. Where do you start looking for the
lookbehind? Shortest first, longest first, or reverse string match?
Greedy or not? Backtrack into capturing results?
Waldemar
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Sebastian Zartner <mailto:sebastianzart...@gmail.com>
September 28, 2013 1:54 PM
I wonder if the discussion about lookbehinds[1] and Marc Harter's
proposal for them[2] in the past led to anything.
I'd really like to see these implemented in ECMAScript specification
and it seems I am not the only one.[3][4][5] This even caused people
to try to mimic them.[6]
So I wanted to pick up the discussion again and ask, what info was
missing that they didn't get specified?
Sebastian
[1]
https://mail.mozilla.org/pipermail/es-discuss/2010-November/012164.html
[2]
https://docs.google.com/document/pub?id=1EUHvr1SC72g6OPo5fJjelVESpd4nI0D5NQpF3oUO5UM
[3]
http://stackoverflow.com/questions/12273112/will-js-regex-ever-get-lookbehind
[4]
http://stackoverflow.com/questions/13993793/error-using-both-lookahead-and-look-behind-regex
[5] http://regexadvice.com/forums/thread/85210.aspx
[6] http://blog.stevenlevithan.com/archives/mimic-lookbehind-javascript
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