Re: Issue: ARRAY-TYPE-ELEMENT-TYPE-SEMANTICS (Version 9)

[masinter.pa@Xerox.COM]

Even though all implementations "must have some code" that does the
upgrading, the code need not be a Lisp function. For example, KCL might do
the upgrading in C, or an implementation might simply upgrade all array
element types to T. 

There's a cost associated with adding functions to the LISP package,
including them in the documentation and specification beyond the cost of
requiring all implementations to write them -- the cost is in the overhead
of testing, documentation, user understanding, burden on implementation
model. The benefit of UPGRADE-ARRAY-ELEMENT-TYPE--namely, that it doesn't
CONS as much as the portable definition--seems very small and I don't think
it outweighs the cost.