> > In ES5, it should be a syntax error. The positive look-ahead is an > Assertion, not an Atom, and quantifiers can only be applied to Atoms. > In ES3, the regexp will not match the string literal. Putting > quantifiers on look-aheads is always unnecessary in ECMAScript, since > it's always equivalent to either requiring zero or one match of the > lookahead. > > The "web reality" is that browser RegExp engines follow the ES3 syntax > for this case.
OK, thanks! I'll create 2 parsers, for web-reality and ES5 strict. Thanks. On Sun, Oct 23, 2011 at 6:03 AM, Lasse Reichstein < [email protected]> wrote: > On Sat, Oct 22, 2011 at 5:30 PM, Yusuke Suzuki <[email protected]> wrote: > >> BTW, I thought that the example in >> http://wiki.ecmascript.org/doku.php?id=strawman:match_web_reality_spec >> exec(/(?=a)+/, ""); >> should return false. Is it right? > > In ES5, it should be a syntax error. The positive look-ahead is an > Assertion, not an Atom, and quantifiers can only be applied to Atoms. > In ES3, the regexp will not match the string literal. Putting > quantifiers on look-aheads is always unnecessary in ECMAScript, since > it's always equivalent to either requiring zero or one match of the > lookahead. > > The "web reality" is that browser RegExp engines follow the ES3 syntax > for this case. > > /L > >> >> On Sat, Oct 22, 2011 at 5:04 AM, Allen Wirfs-Brock >> <[email protected]> wrote: >>> >>> On Oct 20, 2011, at 10:17 PM, Yusuke Suzuki wrote: >>> >>> >>> And, I tried to implement RegExp.prototype.compile, but ES5 and ES3 >>> not defined its standard behavior and I thought compile method is >>> changing RegExp#source / #global / #ignoreCase / #multiline which >>> writable attribute are false and breaking ES5 PropertyDescriptor >>> system, so I created template, but not implemented it. >>> https://github.com/Constellation/iv/commit/7cbc22474ada389a3ac8ab5d3ad5df38bed8a583 >>> >>> >>> >>> see http://wiki.ecmascript.org/doku.php?id=harmony:regexp_match_web_reality >>> >>> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> >
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