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49 lines
779 B
49 lines
779 B
12 years ago
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/*
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* E5 Section 15.10.2.8 notes on backtracking for lookaheads.
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*/
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var t;
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/*===
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aaa
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aba a
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===*/
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t = /(?=(a+))/.exec('baaabac');
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print(t[0], t[1]);
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t = /(?=(a+))a*b\1/.exec('baaabac');
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print(t[0], t[1]);
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/*===
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baaabaac ba undefined abaac
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===*/
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t = /(.*?)a(?!(a+)b\2c)\2(.*)/.exec('baaabaac');
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print(t[0], t[1], t[2], t[3]);
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/*===
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xy x undefined
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xz undefined x
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===*/
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t = /(?=(x))xy|(?=(x))xz/.exec('xy');
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print(t[0], t[1], t[2]);
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t = /(?=(x))xy|(?=(x))xz/.exec('xz');
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print(t[0], t[1], t[2]);
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/*===
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abab ab
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null object
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===*/
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/* lookahead captures 'ab' */
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t = /(?=(ab|abc))\1\1/.exec('abab');
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print(t[0], t[1]);
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/* lookahead still captures 'ab' and backrefs fail; lookahead never tries to capture 'abc' */
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t = /(?=(ab|abc))\1\1/.exec('abcabc');
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print(t, typeof t);
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