> Well, this approach basically is the 'annotate approach, except instead of having a separate basic data type - a "tagged" object - you just use cons cells, where the car is the type and the cdr the rep.
Except for the case where (isa R T), where (annotate T R) returns R directly:
This isn't a fundamental difference. Just as 'annotate could as easily create a new doubly-wrapped object, 'annotate-cons can as easily not cons when the type is the same.
(def annotate-cons (typ val)
(if (isa val typ) val (cons typ val)))
