#750 MAPCAN/MAPCON Edge cases

[Alexander Fedorov]

MAPCAN/MAPCON functions have two edge cases which are not correctly handled in clisp.

(mapcan #'identity '(1 2 3))  ; should error, returns 3 instead
(mapcon #'car '(1 2 3))       ; same

(setf *print-circle* t)

;; This returns #1=(1 2 . #1#), which is correct
(let ((lst (list 1 2)))
  (flet ((f (x)
           (declare (ignore x))
           lst))
    (apply #'nconc (mapcar #'f '(1 2)))))

;; Should be equivalent to the previous example, but hangs instead.
(let ((lst (list 1 2)))
  (flet ((f (x)
           (declare (ignore x))
           lst))
    (mapcan #'f '(1 2))))

Also please see https://gitlab.common-lisp.net/ansi-test/ansi-test/-/issues/39 .

Tested on clisp 2.49:

[1]> (lisp-implementation-version)
"2.49.93+ (2018-02-18) (built on lcy02-amd64-055.buildd [127.0.1.1])"

[Bruno Haible]

I agree with at least the first part of your example: NCONC should validate that its arguments except the last one are lists. MAPCAN and MAPCON should check the intermediate results accordingly.