Subset types, at least in that form you have shown, do not exist in Common Lisp. That's a very MLish feature, and Perl keeps on surprising me :-) Do another, m

Subset types, at least in that form you have shown, do not exist in Common Lisp. That's a very MLish feature, and Perl keeps on surprising me :-) Do another, more elaborate one when you have time. Would love to learn new things.