Derived function type used as an assertion

[Stas Boukarev]

(defun redefine ()
  "123")

(defun foo ()
  (unwind-protect (redefine) 1))

compiled in one go in a single file,
then
(progn (defun redefine () "12") (foo))
=>
The value "12" is not of type (SIMPLE-ARRAY CHARACTER (3)).

[Stas Boukarev (stassats)]

(defun foo ()
  (let ((x (redefine)))
    x))

is enough.

[Stas Boukarev (stassats)]

Of course it's undefined what happens to redefined functions from the same file, but this makes interactive development impossible, especially when the type is specific enough. And there seems to be no way to turn it off, and it does not always happen.

[Charles (karlosz)]

One can now set *derive-function-types* to NIL from its default of :SAME-FILE.