sub foo # requires interfaces IntA, IntB
{
  my ($self) = @_;
  IntA::validate($self);
  IntB::validate($self);
}
[download]

Excellent! I am impressed - a very simple, concise and - as far as I can tell - robustly versatile approach. Seems to be the perfect distribution of responsibilities. It certainly deserves attention - if it doesn't get much here, please repost it as a root node. I'm very curious to hear the gurus with theoretical background poke at this and comment on it.

Makeshifts last the longest.