Lecture 23 : Two-way family trees


;; A person is a (make-person string famtree famtree list-of-person)
(define-struct person (name mother father kids))

;; A famtree is either
;; - 'unknown, or
;; - a person

;; A list-of-person is either
;; empty, or
;; (cons person list-of-person)


Now, create an example family tree for a person named Judy whose
mother is named Brenda and whose father is unknown.

  (define Bper (make-person "Brenda" 'unknown 'unknown empty))
  (define Jper (make-person "Judy" Bper 'unknown empty))
  (set-person-kids! Bper (list Jper))

;; add-child-to-mother : person string -> void 
;; creates person with given name and the given person as their mother
;; EFFECT: changes kids component of given mother
(define (add-child-to-mother mothper cname)
  (local [(define childper (make-person cname mothper 'unknown empty))] 
    (set-person-kids! mothper (cons childper (person-kids mothper)))))

  Summary : if two pieces of data need to contain each other, you have
  to create at least one piece first, define the second to refer to
  the first, then use set-structure! to make the first refer to the
  second.

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Testing void functions

(add-child-to-mother Bper "Eddie") "expects to give Brenda a new
                                    child with Brenda as the child's
                                    mother"

(print the data structure when you're done to prove it's so)

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