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Re: A little help on look behinds

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  • flo.gehrke
    ... Thanks, diodeom! It was clear, however, why the expression fails at line #9. But the question was: Why doesn t it match line #10 and #11? Why doesn t the
    Message 1 of 21 , Oct 17, 2011
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      --- In ntb-clips@yahoogroups.com, "diodeom" <diomir@...> wrote:
      >
      > I'd guess you're running this pattern in the (Ctrl+R) dialog
      > box instead of in a clip...

      Thanks, diodeom!

      It was clear, however, why the expression fails at line #9. But the question was: Why doesn't it match line #10 and #11? Why doesn't the engine just skip the mismatch?

      If we start anew from the beginning of line #10 then line #11 will be selected. But when starting from the beginning of the subject string the verb seems to nail the cursor to the beginning of line #8.

      Moreover, it doesn't seem to be a matter of running it in the dialog box or in a clip. For example...

      ^!Info ^$GetDocListAll("(?s).+?\R\K(?=\]\]\]|\[\[\[)(*COMMIT)(?-s)\]\]\].*\R";"$0\r\n")$

      achieves only two matches as well: line #5 and #7 (I've omitted '\A' here because it doesn't change the result no matter if used in the dialog or a clip).

      Well, I don't want to tax your patience too much with my slow-wittedness. Don't ask -- just be surprised! Obviously, that's the way the verb is designed to work. It prevents the engine from making any further attempt at all once it has failed at any position. I hope I've learned the lesson...

      Flo

      PS Also thanks to Sheri for her latest reply!

      ---

      > Flo wrote:
      > >
      > > --- In ntb-clips@yahoogroups.com, Sheri <silvermoonwoman@> wrote:
      > > >
      > > > (*COMMIT) says the rest of the pattern must match from here without
      > > > backtracking...I guess you could say it creates an anchor in
      > > > the middle of the pattern.
      > >
      > > Sheri,
      > >
      > > I would be grateful for some more explanations about that verb '(*COMMIT).
      > >
      > > I've tested your clip...
      > >
      > > (?s)\A.+?\R\K(?=\]\]\]|\[\[\[)(*COMMIT)(?-s)\]\]\].*\R
      > >
      > > against the following text which is quite similar to John's first sample. For our discussion, I've added line numbers (to be removed when testing):
      > >
      > > 1 First line
      > > 2
      > > 3 [valid line]
      > > 4
      > > 5 ]]] remove
      > > 6
      > > 7 ]]] remove
      > > 8
      > > 9 [[[ valid line
      > > 10 more valid lines
      > > 11 ]]] valid line.
      > > 12
      > > 13 [[[ valid line
      > >
      > > It's quite clear for me why the clip removes line #5 and #7 but not #9. But I still can't see why it doesn't remove line #11.
      > >
      > > If we omit the '\K' we can see two matches:
      > >
      > > - 1. from start of string to end of line #5
      > >
      > > - 2. line #6 till end of line #7
      > >
      > > Next, line #8 and #9 are not matched because line #9 doesn't start with ']]]'.
      > >
      > > But WHY doesn't the clip jump over that mismatch and moves on selecting line #10 and #11? IMHO, line #10 should be matched with '(?s)\A.+?\R\K(?=\]\]\]|\[\[\[)' (with or without '\A'), and the following '(?-s)\]\]\].*\R'. Why on earth is '(*COMMIT)' preventing this?
      > >
      > > Thanks for any light you can shed on this!
      > >
      >
      >
      > I'd guess you're running this pattern in the (Ctrl+R) dialog box instead of in a clip -- where it's meant to ***capture or fail*** only once (on the very first instance of either [[[ or ]]]).
      >
      > If you click "Find Next" after #5 and #7, notice that your beginning position for the next attempt is on or after line #7. After the first available alternative "[[[" is spotted by the look-ahead now on line #9, (*COMMIT) demands that at this very location either "]]]" should be found or else the whole pattern should abandon any further matching attempts. Obviously, "[[[" ain't the required "]]]" so the pattern fails by design.
      >
    • John Shotsky
      Flo, It turns out that your suggestion fails at times, and takes out ]]] which IS preceded by a [[[ somewhere above it in the text. If [[[ were the first thing
      Message 2 of 21 , Oct 17, 2011
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        Flo,

        It turns out that your suggestion fails at times, and takes out ]]] which IS preceded by a [[[ somewhere above it in the
        text. If [[[ were the first thing in the file, it should do nothing.
        ^!Replace "(?s)(?!\[{3}).{1,}?\K\]{3}\R" >> "" WRS

        I didn't take time to troubleshoot it, as the '*COMMIT' version does not fail. I just mention it in case you want to
        play with it some more.

        Regards,
        John

        From: ntb-clips@yahoogroups.com [mailto:ntb-clips@yahoogroups.com] On Behalf Of flo.gehrke
        Sent: Monday, October 17, 2011 03:49
        To: ntb-clips@yahoogroups.com
        Subject: [Clip] Re: A little help on look behinds


        --- In ntb-clips@yahoogroups.com <mailto:ntb-clips%40yahoogroups.com> , "diodeom" <diomir@...> wrote:
        >
        > I'd guess you're running this pattern in the (Ctrl+R) dialog
        > box instead of in a clip...

        Thanks, diodeom!

        It was clear, however, why the expression fails at line #9. But the question was: Why doesn't it match line #10 and #11?
        Why doesn't the engine just skip the mismatch?

        If we start anew from the beginning of line #10 then line #11 will be selected. But when starting from the beginning of
        the subject string the verb seems to nail the cursor to the beginning of line #8.

        Moreover, it doesn't seem to be a matter of running it in the dialog box or in a clip. For example...

        ^!Info ^$GetDocListAll("(?s).+?\R\K(?=\]\]\]|\[\[\[)(*COMMIT)(?-s)\]\]\].*\R";"$0\r\n")$

        achieves only two matches as well: line #5 and #7 (I've omitted '\A' here because it doesn't change the result no matter
        if used in the dialog or a clip).

        Well, I don't want to tax your patience too much with my slow-wittedness. Don't ask -- just be surprised! Obviously,
        that's the way the verb is designed to work. It prevents the engine from making any further attempt at all once it has
        failed at any position. I hope I've learned the lesson...

        Flo

        PS Also thanks to Sheri for her latest reply!

        ---

        > Flo wrote:
        > >
        > > --- In ntb-clips@yahoogroups.com <mailto:ntb-clips%40yahoogroups.com> , Sheri <silvermoonwoman@> wrote:
        > > >
        > > > (*COMMIT) says the rest of the pattern must match from here without
        > > > backtracking...I guess you could say it creates an anchor in
        > > > the middle of the pattern.
        > >
        > > Sheri,
        > >
        > > I would be grateful for some more explanations about that verb '(*COMMIT).
        > >
        > > I've tested your clip...
        > >
        > > (?s)\A.+?\R\K(?=\]\]\]|\[\[\[)(*COMMIT)(?-s)\]\]\].*\R
        > >
        > > against the following text which is quite similar to John's first sample. For our discussion, I've added line
        numbers (to be removed when testing):
        > >
        > > 1 First line
        > > 2
        > > 3 [valid line]
        > > 4
        > > 5 ]]] remove
        > > 6
        > > 7 ]]] remove
        > > 8
        > > 9 [[[ valid line
        > > 10 more valid lines
        > > 11 ]]] valid line.
        > > 12
        > > 13 [[[ valid line
        > >
        > > It's quite clear for me why the clip removes line #5 and #7 but not #9. But I still can't see why it doesn't remove
        line #11.
        > >
        > > If we omit the '\K' we can see two matches:
        > >
        > > - 1. from start of string to end of line #5
        > >
        > > - 2. line #6 till end of line #7
        > >
        > > Next, line #8 and #9 are not matched because line #9 doesn't start with ']]]'.
        > >
        > > But WHY doesn't the clip jump over that mismatch and moves on selecting line #10 and #11? IMHO, line #10 should be
        matched with '(?s)\A.+?\R\K(?=\]\]\]|\[\[\[)' (with or without '\A'), and the following '(?-s)\]\]\].*\R'. Why on earth
        is '(*COMMIT)' preventing this?
        > >
        > > Thanks for any light you can shed on this!
        > >
        >
        >
        > I'd guess you're running this pattern in the (Ctrl+R) dialog box instead of in a clip -- where it's meant to
        ***capture or fail*** only once (on the very first instance of either [[[ or ]]]).
        >
        > If you click "Find Next" after #5 and #7, notice that your beginning position for the next attempt is on or after line
        #7. After the first available alternative "[[[" is spotted by the look-ahead now on line #9, (*COMMIT) demands that at
        this very location either "]]]" should be found or else the whole pattern should abandon any further matching attempts.
        Obviously, "[[[" ain't the required "]]]" so the pattern fails by design.
        >



        [Non-text portions of this message have been removed]
      • Sheri
        Flo, do you remember the G? I think (*COMMIT) is like that, except the match position within the subject is established dynamically after matching what s
        Message 3 of 21 , Oct 17, 2011
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          Flo, do you remember the \G? I think (*COMMIT) is like that, except the
          match position within the subject is established dynamically after
          matching what's before the (*COMMIT).

          Remember that PCRE does not itself find multiple matches. NoteTab's
          functions and commands that find or replace multiple matches require
          NoteTab to execute PCRE multiple times at different starting positions.
          NoteTab's general behavior in doing so is to advance the cursor after a
          successful match (to find more matches past that match). NoteTab only
          advances the cursor and continues looking for more matches after a
          successful match, it doesn't do it after a "No Match" result.

          I believe \A matches only at the very start of a subject. Don't have
          time to play with GetDocListAll til later, but I think the only way more
          than one match could be found using a pattern starting with \A would be
          if NoteTab were sending PCRE different subject strings on each execution
          (not just different starting positions). Would surprise me if it is.

          Regards,
          Sheri
        • flo.gehrke
          ... John, No surprise -- I took your message literally. In #22150, you spoke of one instance where ]]] is NOT preceded anywhere in the file by a [[[. That is
          Message 4 of 21 , Oct 17, 2011
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            --- In ntb-clips@yahoogroups.com, "John Shotsky" <jshotsky@...> wrote:
            >
            > Flo,
            >
            > It turns out that your suggestion fails at times, and takes out ]]]
            > which IS preceded by a [[[ somewhere above it in the
            > text....

            John,

            No surprise -- I took your message literally. In #22150, you spoke of "one instance where ]]] is NOT preceded anywhere in the file by a [[[. That is the only ]]] that should be removed. It is always the first one."

            Well, here's another idea: It removes any line (empty or not) starting with ']]]' which is NOT preceeded by '[[['. All lines starting with '[[[' and being followed somewhere by a closing ']]]' are left untouched.

            ^!Replace "(?s)^\[{3}.*?\]{3}\K|(?-s)^\]{3}.*(\R{1,}|\Z)" >> "" WARS

            Tested with...

            Beginning of file
            [This text is to remain]
            ]]]
            ]]] remove
            [[[ valid line
            valid line ]]]
            [[[ valid line ]]]
            [[[
            valid line
            ]]]
            ]]] remove

            Line #3, #4, and #11 will be removed.

            Regards,
            Flo
          • flo.gehrke
            ... Oh yes, I do remember G ! Great discussion in Oct 2008 (see #18566) Probably, this could explain why, at times, they call (*COMMIT) an anchor. Thanks
            Message 5 of 21 , Oct 17, 2011
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              --- In ntb-clips@yahoogroups.com, Sheri <silvermoonwoman@...> wrote:
              >
              > Flo, do you remember the \G? I think (*COMMIT) is like that,...

              Oh yes, I do remember '\G'! Great discussion in Oct 2008 (see #18566)

              Probably, this could explain why, at times, they call '(*COMMIT)' an anchor.

              Thanks again for your explanations. It's always a pleasure to learn more about NT's hidden secrets from you :-)

              Flo
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