Well, I played around with this some more. I got it working but it makes the code a lot uglier. For example, here's what I have to generate nested iterators now:

    my $it1 = $fp->next_parseable_file;
    while (my $file1 = $it1->next) {
      print $fp->short_name($file1) . "\n";
      my $it2 = $fp->next_nonparseable_file;
      while (my $file2 = $it2->next) {
        print $fp->short_name($file2) . "\n";
      }
    }
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Whereas before, I just had:

    while ($fp->next_parseable_file) {
      print $fp->short_name . "\n";
      while ($fp->next_nonparseable_file) {
        print $fp->short_name . "\n";
      }
    }
[download]

The iterators now have to be created separately from the while loop. And I'm stuck passing around the $file to the short_name method.

I get that having the separation in logic the way you describe is probably more ideal from a logical perspective. But maybe this is a case where some rules should be broken? I don't have enough experience to say. Or maybe there is some trickery I could invoke to get the best of both worlds?