;;; /tmp/mc.lisp
(defpackage :mc-test
  (:use :cl )
  (:export ))
(in-package :mc-test)

(defun positive-integer-qualifier-p (method-qualifiers)
  (and (= (length method-qualifiers) 1)
       (typep (first method-qualifiers) '(integer 0 *))))
(define-method-combination example-method-combination ()
  ((methods positive-integer-qualifier-p))
  `(progn ,@(mapcar #'(lambda (method)
                        `(call-method ,method))
                    (stable-sort methods #'<
                                 :key #'(lambda (method)
                                          (first (method-qualifiers method)))))))
(defgeneric quux (a) (:method-combination example-method-combination))
(defmethod quux 0 (a) (format t "hi there"))
(defmethod quux 1 (a) (format t "bye?"))

(defun main ()
  (quux 4))

;;
CL-USER(1): (load (compile-file "/tmp/mc.lisp"))
CL-USER(2): (in-package :mc-test)
MC-TEST(3): (main)
#| =>
debugger invoked on a SB-PCL::LONG-METHOD-COMBINATION-ERROR in thread
#<THREAD "main thread" RUNNING {10005C05B3}>:
  More than one method of type METHODS with the same specializers.
See also:
  The ANSI Standard, Macro DEFINE-METHOD-COMBINATION

Type HELP for debugger help, or (SB-EXT:EXIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [ABORT] Exit debugger, returning to top level.

((SB-PCL::EMF QUUX) #<unused argument> #<unused argument> #<unused argument>)
   error finding frame source:   Don't know how to use a DEBUG-SOURCE without a namestring or a form.
                               This is probably a bug in SBCL itself.
                               (Alternatively, SBCL might have been corrupted
                               by bad user code, e.g. by an undefined Lisp
                               operation like (FMAKUNBOUND 'COMPILE), or by
                               stray pointers from alien code or from unsafe
                               Lisp code; or there might be a bug in the OS or
                               hardware that SBCL is running on.) If it seems
                               to be a bug in SBCL itself, the maintainers
                               would like to know about it. Bug reports are
                               welcome on the SBCL mailing lists, which you can
                               find at <http://sbcl.sourceforge.net/>.
   source: NIL
0] :0 |#