CS 1101: Programming Language Concepts
Documentation and Data Definition Example

A data definition with examples of the data

;; a coord (literally: coordinate) is a structure
;;  (make-coord num num)

(define-struct coord (x y))

;; Examples of coords
(make-coord 0 8)
(make-coord -1 4)

A program with a contract, purpose, and test cases

;; move-coord-vertical : coord number -> coord
;; consumes a coordinate and a number by which to move the coordinate in the
;;   vertical position and produces a coordinate in the new position.
(define (move-coord-vertical a-coord delta)
  (make-coord (coord-x a-coord) 
	      (+ (coord-y a-coord) delta)))

;; Test cases
(move-coord-vertical (make-coord 0 8) 5) ;; expect (make-coord 0 13)
(move-coord-vertical (make-coord 4 -2) 7) ;; expect (make-coord 4 5)
(move-coord-vertical (make-coord -1 4) -4) ;; expect (make-coord -1 0)