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Re^4: Regex fun

by JavaFan (Canon)
on Dec 15, 2009 at 22:13 UTC ( [id://812944]=note: print w/replies, xml ) Need Help??


in reply to Re^3: Regex fun
in thread Regex fun

Sorry, I don't understand—not the reason for what?
Quoting myself where I am quoting you:
the variable that contains the contents of the first capture group is $1, but that's empty until the capture has completed.
You're claiming $1 is "empty" until the the capture has completed. I'm pointing that the in the case of the OP, said first capture has completed.
Do you mean ‘re-entrant’?
No, I don't. The current regexp-engine isn't re-entrant.

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Re^5: Regex fun
by JadeNB (Chaplain) on Dec 15, 2009 at 22:41 UTC
    You're claiming $1 is "empty" until the the capture has completed. I'm pointing that the in the case of the OP, said first capture has completed.

    I guess that the quotes around ‘empty’ are to point out that, besides the unusual choice of word (in place of ‘undefined’), it's not true—sorry, I'll correct that.

    I agree that Hena's second solution doesn't suffer from the problem that I mentioned; but the post particularly asks for a single-regex solution, and I was just mentioning why the obvious substitute, /\+([0-9]+)[$bases]{$1}/, for the non-working regex /\+([0-9]+)[$bases]{\1}/, doesn't work. (Nobody suggested it anyway, so I guess it was pretty unclear what I was talking about.)

    No, I don't. The current regexp-engine isn't re-entrant.

    Yes, which is why I thought that the final word in “the regexp engine was no longer recursive” might be ‘re-entrant’. :-) (I don't know enough history to know whether it ever was re-entrant, so, for all I knew, the grammar was correct.) I was particularly confused because Perl 5.10 newly allows for recursive regexes, which I confused with the regex engine itself being recursive; but ikegami clarified.

      The regexp engine has never been re-entrant. It has only mattered since we have /(?{ })/ and /(??{ })/, before that, there was no way to start another match before the first one was finished. So even if it were re-entrant, you couldn't use the fact.

      This:

      /PAT1 (??{m!PAT2!}) PAT3/
      is very likely to do unexpected things due to the regexp engine not being re-entrant.

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