Behaviour of a structure whose type predicate has the same name as its slot's accessor

[moon-chilled]

Quoth a comment from sbcl source:

        ;; Some adventurous soul has named a slot so that its accessor
        ;; collides with the structure type predicate. ANSI doesn't
        ;; specify what to do in this case. As of 2001-09-04, Martin
        ;; Atzmueller reports that CLISP and Lispworks both give
        ;; priority to the slot accessor, so that the predicate is
        ;; overwritten. We might as well do the same (as well as
        ;; signalling a warning).