int product (int x, int y) {
  return x * y;
}

char *product (char *company, int prodID) {
  /*
    magic to return name of product
    related to prodID in the given company
  */
}

##</code><code>##

sub foo {
  die "foo() needs at least one argument" if !@_;
  (my($x,$), local($z)) = @_;
  $y ||= 10;
  $z ||= $x * $y;
  # ...
}

##</code><code>##

sub foo (
  my($x) :req,
  my($y) ||= 10,
  local($z) ||= ($x * $y)
) {
  # ...
}