I'd really like to be able to put a bit more logic into my regexes. At the moment, I guess I can do this with the (??{ ... }) assertion.

I recently answered a question about inserting newlines every 80 characters, or at the end of the previous word (if we're in the middle of one). What I wanted my solution to be was something like:

That's not as easy as it seems. In a couple of minutes, I'm going to attempt to write a solution that does this. And then you'll see why I'd like to be able to go to a specific point in the regex, or at least be able to break out of a quantifier.

_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

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Re: goto() in regexes
by chipmunk (Parson) on Aug 27, 2001 at 19:21 UTC
    Here's a simple substitution that inserts a newline every 80 characters, or at the end of the previous word. ('word' here is a sequence of non-whitespace characters, since that's usually what you want for wrapping.) s/\G(.{1,80})(?<=\S)\s+/$1\n/gm;
[reply]
[d/l]
      I don't think the look-behind assertion and anchor are necessary (the anchor actually causes it to terminate early on certain boundary cases with newlines): 
      s/(.{0,79}\S\s+)/$1\n/gm

      [download]
      ... I could be wrong :) 
         MeowChow                                   
               s aamecha.s a..a\u$&owag.print
[reply]
[d/l]
      Oh, ****.

      _____________________________________________________
      Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
      s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

[reply]
Re: goto() in regexes
by japhy (Canon) on Aug 27, 2001 at 17:27 UTC
    Here's what I got to work. It's pretty self-explanatory. 
    #!/tmp/bleadperl/bin/perl -w 

use re 'eval';

my $re;
my $len = 20;

$_ = "this is a long string, and I want to insert newlines every 20 ch
+ars";

$re = qr{
  (??{ '\b\w{1,' . ($len - ($+[0] - $-[0])) . '}\b' })
  (?(?{ ($+[0] - $-[0]) < $len })
    (??{ '\W{0,' . ($len - ($+[0] - $-[0])) . '}' })
    (?(?{ ($+[0] - $-[0]) < $len })
      (?(?=
        (??{ '\b\w{1,' . ($len - ($+[0] - $-[0])) . '}\b' }))
        (??{ $re })
      )
    )
  )
}x;

s{($re)}{$1\n}xg;

print;

    [download]
    What I want to be able to say is something like: 
    $re = qr{
  (??{ '\b\w{1,' . ($len - ($+[0] - $-[0])) . '}\b' })
  (?(?{ ($+[0] - $-[0]) < $len })
    (??{ '\W{0,' . ($len - ($+[0] - $-[0])) . '}' })
  )
  (?(?{ ($+[0] - $-[0]) == $len })
    (?&done)
  )
}x;

s{($re+)(?%done)}{$1\n}xg;

    [download]
    That code creates two new regex assertions, (?%LABEL) and (?&LABEL). The first defines a position in the regex, and the second forcibly moves the regex engine to that position. Now, perhaps this is too much power to wield, but I like power. If people don't like this, then I would do something like: 
    $re = qr{
  (??{ '\b\w{1,' . ($len - ($+[0] - $-[0])) . '}\b' })
  (?(?{ ($+[0] - $-[0]) < $len })
    (??{ '\W{0,' . ($len - ($+[0] - $-[0])) . '}' })
  )
  (?(?{ ($+[0] - $-[0]) == $len }) (?;) )
}x;

s{($re+)}{$1\n}xg;

    [download]
    Here, the (?;) assertion means "jump out of the enclosing quantifier". This means that we're making a while loop out of the quantifier: 
    while (1)
  do_pattern($re);
  if ($seen_qu_semi) { last }
}

    [download]
    Again, perhaps this is too much power. But I really like this power. However, perhaps I could simply develop some rules by which to munge the label/goto into an ugly format; or at least the out-of-quant into an ugly format.

    In the words of Tim "The Tool Man" Taylor, "more power! arr arr arr!"

    Update: I found that I could write it like so: 

    $re = qr{
  (??{ '\b\w{1,' . ($len - ($+[0] - $-[0])) . '}\b' })
  (?(?{ ($+[0] - $-[0]) < $len })
    (??{ '\W{0,' . ($len - ($+[0] - $-[0])) . '}' })
  )
}x;

s{
  (
    (?:
      (?(?{ ($+[0] - $-[0]) == $len })(?!))
      $re
    )+
  )
}{$1\n}xg;

    [download]
    That seems easier to read. Plainer. More logical. It's a real while loop. I like it. Perhaps I'll create a filter.

    _____________________________________________________
    Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
    s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

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