(defpackage :vector-stuff
  (:use :cl)
  (:export #:dec))
(in-package :vector-stuff)
(defmacro dec ((&rest vectors) &body body)
  `(let* ,(loop for vector in vectors
                for n from 1
                for forced = (gensym "FORCED-VECTOR")
                for x-name = (alexandria:format-symbol *package* "X~d" n)
                for y-name = (alexandria:format-symbol *package* "Y~d" n)
                appending `((,forced ,vector)
                            (,x-name (aref ,forced 0))
                            (,y-name (aref ,forced 1))))
     ,@body))


(in-package :cl-user)
(let ((v1 (vector 1 2))
      (v2 (vector 3 4)))
  (vector-stuff:dec (v1 v2)
    (vector (+ x1 x2)
            (+ y1 y2))))