(in-package :cl-user)

(defgeneric add (x y)
  (:method ((x integer) (y integer))
    (+ x y))

  (:method ((x integer) (y vector))
    ;; ...
    ))

(defgeneric make-adder (x y)
  (:method ((x integer) (y integer))
    (lambda (x y)
      (+ x y)))
  
  (:method ((x integer) (y vector))
    ;; ...
    ))

(defun test-add ()
  (loop :for i :from 0 :to 10000000
        :for j :from 0 :to 10000000
        :do (add i j)))

(defun test-adder ()
  (let ((adder (make-adder 1 1)))
    (loop :for i :from 0 :to 10000000
          :for j :from 0 :to 10000000
          :do (funcall adder i j))))

;;; Test

CL-USER> (time (test-add))
(TEST-ADD)
took 963,386 microseconds (0.963386 seconds) to run.
During that period, and with 4 available CPU cores,
     963,446 microseconds (0.963446 seconds) were spent in user mode
           1 microseconds (0.000001 seconds) were spent in system mode
 400 bytes of memory allocated.
NIL

CL-USER> (time (test-adder))
(TEST-ADDER)
took 91,878 microseconds (0.091878 seconds) to run.
During that period, and with 4 available CPU cores,
     91,696 microseconds (0.091696 seconds) were spent in user mode
          0 microseconds (0.000000 seconds) were spent in system mode
 400 bytes of memory allocated.
NIL