I'd rewrite it using overload:

package whirly;
use overload ('""' => \&nextchar, fallback => 1);
use strict;
sub new { bless [ '|', '/', '-', '\\' ] }
sub nextchar {
  push @{ $_[0] }, shift @{ $_[0] };
  return $_[0][0];
}
[download]

Used like so:

use whirly;
$waiting = new whirly;
until (file_downloaded()) {
  print $waiting;
}
[download]

$_="goto+F.print+chop;\n=yhpaj";F1:eval