How do you declare a function that doesn't return anything? For instance, a C++ swap function might be declared template <class X> void swap(X &x, X &y);
It would be nice to declare the corresponding Perl6 function as sub swap ($x is rw, $y is rw) returns nothing {...} or something similar. This would be an absolute necessity if you wanted to emulate C++, Java, or any other strongly typed language. Also, it could be useful for causing a compile-time error if someone types something like $z = swap($x, $y); Joe Gottman