sub fact
{
  my $fact_tr; # needs to exist before it gets assigned to
  $fact_tr = sub {
    my ($v, $r) = @_;
    return 1 if $v < 2; # oversimplified
    $fact_tr->($v-1, $v * $r);
  }; # thanks ihb for pointing out the missing semi
  $fact_tr->(@_, 1);
}