sub substrings {
  my $string = shift;

  my @result = ();

  foreach my $start (0..length($string)-1) {
    my $substr = substr($string, $start);
    while (length($substr)) {
        push @result, $substr;
        chop($substr);
    }
  }

  return @result;
}

##</code><code>##

sub substrings {
  local $_ = shift;
  my @result;
  do { push @result, /(?=(.+)$)/sg; chop } while (length);
  return @result;
}