# Be sure that these start clean!
my %bad_r;
my %bad_pos;
@x = split /(?{
    # This populates $^R
    pos()
  })some pattern(??{
    # This returns an impossible pattern for long matches
    if (pos()-$^R < 3
      and not $bad_r{$^R}
      and not $bad_pos{pos()}
    ) {
      "";
    }
    else {
      $bad_r{$^R}++;
      $bad_pos{ pos() }++;
      "no\\bmatch"
    }
  })/, $string;