A GPSetType is a GPType which contains GPAtomicTypes in a set, and is used
as a generic GP type. For more information, see GPType
GPSetTypes implement their set using both a hash table and an array.
if the size of the set is "significantly big", then the hash table
is used to look up membership in the set (O(1), but with a big constant).
If the size is small, then the array is used (O(n)). The dividing line
is determined by the constant START_USING_HASH_BEYOND, which you might
play with to optimize for your system.
Sets up the object by reading it from the parameters stored
in state, built off of the parameter base base.
If an ancestor implements this method, be sure to call
super.setup(state,base); before you do anything else.
Am I compatible with ("fit" with) t? For two atomic
types, this is done by direct pointer equality. For
two set types, this is done by determining if the intersection
is nonempty. A set type is compatible with an atomic type
if it contains the atomic type in its set.