ConstList is one of E's standard table types, and a subtype of EList. A ConstList holds an arbitrary number of references in a particular order, and allows typically constant-time access to any element (identified by number).
Returns a ConstList whose elements are the arguments.
The majority of ConstList's protocol is that of EList. (XXX or is it all?)
XXX not written
Returns a guard which yields only ConstLists whose elements coerce by elementType.
XXX describe element coercion behavior