Add regular expressions lookbehind
sebastianzartner at gmail.com
Wed Oct 2 05:04:20 PDT 2013
As I understand it the problem with lookbehinds are not parentheses but
variable lengths. Therefore many regular expression flavors only allow
fixed-length lookbehinds, which could also be the restriction within
ECMAScript for now. This restriction could then be addressed at a later
> Backtrack into capturing results?
Seems like at least PCRE does that. for parenthesed parts within
On 1 October 2013 00:55, Waldemar Horwat <waldemar at 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 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?
> On 09/28/2013 01:54 PM, Sebastian Zartner wrote:
>> I wonder if the discussion about lookbehinds and Marc Harter's
>> proposal for them 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. This even caused people to try to
>> mimic them.
>> So I wanted to pick up the discussion again and ask, what info was
>> missing that they didn't get specified?
>>  https://mail.mozilla.org/**pipermail/es-discuss/2010-**
>>  https://docs.google.com/**document/pub?id=**
>>  http://stackoverflow.com/**questions/12273112/will-js-**
>>  http://stackoverflow.com/**questions/13993793/error-**
>>  http://regexadvice.com/forums/**thread/85210.aspx<http://regexadvice.com/forums/thread/85210.aspx>
>>  http://blog.stevenlevithan.**com/archives/mimic-lookbehind-**
>> es-discuss mailing list
>> es-discuss at mozilla.org
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