compareTo functions for types

[Alan Gates]

In reworking the types I noticed that the compareTo functions for each 
type are careful to provide an intertype sorting.  For example, from 
DataBag:

public int compareTo(Object other) {
   if (other instanceof DataAtom) return +1;
   if (other instanceof Tuple) return -1;
   if (other instanceof DataBag){
       DataBag bOther = (DataBag) other;
       ...
   }
}

Since a compareTo function is possibly called thousands of times during 
a single sort we really want these to be efficient. Is there a reason 
for all this cross type checking?  Do we have a need to sort Atoms in 
the same container with DataBags?

Alan.