tie $foo, Stack, 'fifo' or die "Could not tie";

$foo = $_ for (1..10);

print while (defined($_ = $foo));

package Stack;

sub TIESCALAR {
  $_[1] =~ /[fl]i[fl]o/i &&  return bless [$_[1],[]], $_[0];
}
sub STORE {
  push @{$_[0]->[1]}, $_[1];
}
sub FETCH {
  return undef unless @{$_[0]->[1]};
  if ($_[0]->[0] =~ /(f|l)i\1o/i) {
    return shift @{$_[0]->[1]};
  }
  else {
    return pop @{$_[0]->[1]};
  }
}