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Re: ...curiosity

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  • Tim Chase
    ... I think the best recipe is knowing the ins and outs of Vim s regexp syntax. It s possible to describe all the cases you describe using (... ) tagging
    Message 1 of 5 , Apr 29, 2007
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      > I am curious whether this kind of meta-regexp is
      > possible with vim:
      > I want to match a certain kind of pattern and want to
      > do "something" with it.
      > The kind of pattern does not describe a group of chars
      > but their relation to each other.
      > Example:
      > I want to search for a number sequence like
      > 1221
      > and also
      > 2332
      > and also
      > 3443
      > and also....
      > Or:
      > I want to find a sequence of five identical characters. The
      > character itsself doesn't matter.

      I think the best "recipe" is knowing the ins and outs of Vim's
      regexp syntax. It's possible to describe all the cases you
      describe using "\(...\)" tagging and back-references, depending
      on the flexibility of your description. However, there's no
      meta-character syntax for sequence-ness. Thus, it's easy to find

      digitA digitB digitB digitA

      patterns with


      but considerably more complex to find

      digitA digitA+1 digitA+1 digitA

      where the 2nd/3rd characters are algorithmically related to the
      1st/4th characters. There are also edge cases about "what should
      X be for '9XX9'". If it was sufficiently complex to find
      something like this, I'd build the regexp with something like
      this untested

      :let x=''
      :let i=0
      :while (i<9)| let x=x.i.(i+1).(i+1).i.'\|' | endwhile
      :let x=x.'9XX9'

      which would yield something like


      in register "x" which could then be dumped into a search using
      control+R followed by "x". One might even do the above algorithm
      directly on "@/" rather than on x.

      For your second case, it's as easy as


      (that's a digit "one" not a letter "ell" or "eye")

      For your first case, I've occasionally thought it would be quite
      handy to have an expression-register in the search as well as in
      the replacement (akin to the "\=" in the replacement) that could
      operate with access to its context, something like


      using an imaginary \=() syntax for expressions. I haven't
      thought long and hard about it; I don't know if it would have
      horrible performance; I don't know if it would have other
      breakages. But it would be darn powerful. :)

      The above would use '9009' as without the modulus ("%"), it would
      search for "910109"

      Alas, no such atrocity exists yet, though you can bet that if it
      did show up, I'd be abusing it left and right :*)

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