Automatic derivation of arbitrary instances for ADTs

[vlstill]

It is possible to uniformly randomly generate words of context-free grammar of given lenght [1, 2]. In the similar spirit, it should be possible to auto-generate values of ADTs, provided the elements contained in the ADT are independent (i.e., presence of some value at some position does not constrain other values; e.g., a binary tree is OK, a binary search tree is not, because of the ordering constraints).