anchor.diff:  
   (define-test test-struct-defaults
       (let ((player-2 (make-baseball-player)))
  -      (assert-equal ___ (baseball-player-position player-2))
  -      (assert-equal ___ (baseball-player-team player-2))
  -      (assert-equal ___ (baseball-player-name player-2))))
  +      (assert-equal :outfield (baseball-player-position player-2))
  +      (assert-equal :red-sox (baseball-player-team player-2))
  +      (assert-equal nil (baseball-player-name player-2))))
   
   
   ;; The accessor names can get pretty long.  It's possible to specify
  
positive.code: (define-test test-abbreviated-struct-access
      (let ((player-3 (make-american-football-player
                       :name "Drew Brees" :position :QB :team "Saints")))
        (assert-equal ___ (nfl-guy-position player-3))))
  
  
  ;; Structs can be defined as EXTENSIONS to previous structures.
  
negative.code:   (let ((player-1 (make-basketball-player
                     :name "larry" :team :celtics :number 33)))
      (assert-equal "larry" (basketball-player-name player-1))
      (assert-equal :celtics (basketball-player-team player-1))
      (assert-equal 33 (basketball-player-number player-1))
      (assert-equal 'basketball-player (type-of player-1))
      (setf (basketball-player-team player-1) :RETIRED)
      (assert-equal :RETIRED (basketball-player-team player-1))))
  
  
  ;; Struct fields can have default values
  