TeachScheme! 2002

 
  Ancestor family trees (p 183ish)

  DATA DEFINITION -- FIRST [use 'unknown instead of empty for base case]

  develop template -- FIRST

  now show how easily we can write functions on this:

  ;; is-in? : symbol family-tree -> boolean

  ;; count : family-tree -> number 

  ;; count-ww2-babies : family-tree -> number
  ;; count those born between 1941 and 1945, inclusive

  PVD 2001:
  This lecture has potential to be a disaster.  If you follow the
  design recipe to the letter, you end up with the following.  A
  person is a (make-person symbol number tree tree) and a tree is
  either 'unknown or a person.  This means they are ... mutually
  recursive.  Bad idea.  That's for tomorrow morning!

  Right defn:
  A ft-node is either
    - 'unknown, or
    - (make-person symbol number symbol ft-node ft-node)

  (define-struct person (name year eye-color mother father)