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:??;