Comment 3 for bug 1001043

Very minor nit: tests should be wrapped in a WITH-TEST. I know nothing in map-tests.impure.lisp uses it yet, but we're glacially moving in the direction of all tests using it -- so all new tests should use it.

General vector leg would benefit from WITH-ARRAY-DATA. There are also more heroic measures that could be taken, eg. widetag dispatch, but WITH-ARRAY-DATA gets most of the way there.

Performance comparison with the open-coded version from seqtran.lisp would be interesting. I suspect it still wins big for unboxed vectors, but probably not so much for others.

These are non-critical observations. If you want to push this further, I'm happy to offer pointers, but I think this can go in pretty much as-is otherwise. Obviously nothing prevents from going further at a later date either. :)