introducing typevar into common lisp

typevar.lisp

(with-typevar <coordinate> (<t>) (<vector-+>)
  (defstruct <coordinate>
    (x 0 :type <t>)
    (y 0 :type <t>))

  (declaim (ftype (function (<coordinate> <coordinate>) <coordinate>) <vector-+>))
  (defun <vector-+> (v w)
    (match* (v w)
      (((<coordinate> x1 y1) (<coordinate> x2 y2))
        (<coordinate> (+ x1 x2) (+ y1 y2))))))

(instantiate '<coordinate> fixnum)
(instantiate '<coordinate> float)

;;; expected-result:

(defstruct coordinate/fixnum
  (x 0 :type fixnum)
  (y 0 :type fixnum))

(declaim (ftype (function (coordinate/fixnum coordinate/fixnum) coordinate/fixnum) vector-+/fixnum))
(defun vector-+/fixnum (v w)
  (match* (v w)
    (((coordinate/fixnum x1 y1) (coordinate/fixnum x2 y2))
      (coordinate/fixnum (+ x1 x2) (+ y1 y2))))))

(defstruct coordinate/float
  (x 0 :type float)
  (y 0 :type fioat))

(declaim (ftype (function (coordinate/float coordinate/float) coordinate/float) vector-+/float))
(defun vector-+/float (v w)
  (match* (v w)
    (((coordinate/float x1 y1) (coordinate/float x2 y2))
      (coordinate/float (+ x1 x2) (+ y1 y2))))))