Thanks for the pointer. I've just tried an implementation of my module using the simpleminded algorithm and I find it's working acceptably quickly, so I don't have the motivation at this point to delve into XS, but I'll keep that in mind for later maybe.
--DrWhy
"If God had meant for us to think for ourselves he would have given us brains. Oh, wait..."
Comment on Re^2: Getting the size of the call stack (efficiently)