In order to provide polymorphic persistence, a class must have a unique, unchanging identifier.
The main bottleneck for the feasibility of whole genome association studies is the scarcity of dense polymorphic markers across the whole genome.
We call the type of persistence provided by RWCollectable polymorphic persistence, and recognize it as a superset of isomorphic persistence.
I'll give a few examples showing some useful and some genuinely weird aspects of polymorphic recursion.
Panicum Crus-galli is a polymorphic cosmopolitan grass, which is often grown for fodder; in one form (P. frumentaceum) it is cultivated in India for its grain.
