Comment 2 for bug 659173

Actually, let's go a step further here: (lambda (x) (if (integerp x) (logand x 31) (car x))) has type (function ((or integer list)) (values t)). It may be used when a (function (integer) (values (mod 32))) is expected with no problem. But (lambda (x) (if (integerp x) (code-char x) (car x))) also has type (function ((or integer list)) (values t)), and clearly may NOT be used in such a situation. This is not the line of argument from CLHS, but does demonstrate the utter futility of expecting any serious level of "type safety" from (setf fdefinition) or (setf symbol-function) beyond simply ensuring that the value is a subtype of FUNCTION.

Can we redefine this in terms of the default policy and trust in FTYPE declarations at the call site, rather than in terms of the FDEFINITION and SYMBOL-FUNCTION accessors, or simply declare the bug to be invalid?