Question

It comes from my homework assignments. There is a family tree

                             a  +  b
                         /   |    |   \ 
                        c+u  d+c  e+w  f
                     / | \        / \
                 m+x  n+y  o      p  q
                  |
                  r

a and b is the oldest. and every married people the second person is not part of the original family.
Now I need to write the spouse, sibling, children ,grandchildren, parents and grandparents function.

I wrote the list as below:
( (father mother) chlid1 child2 child3)

(((a b) c d e f) ((c u) m n o) ((d v) nil) ((e w) p q) (f nil) ((m x) r) ((n y) nil) (o nil) (p nil) (q nil)  )

I have some problems with sibling function, here is my code.

(defun sibling  (arglst lst)  
 (cond
        ((eql 
             arglst (cdr (car lst))) 
                 (rest (cdr lst))
         )
   (T (sibling (rest lst) arglst))

)

I knew it was wrong, but I don’t how to revise it.. and I also need some help with other functions. hope can get some hints from u guys.

Answer 1

Since this is homework, I won’t give the full solution, but this should suffice for you to solve the rest:

(defparameter *family* '(((a b) c d e f)
                         ((c u) m n o)
                         ((d v) nil)
                         ((e w) p q)
                         (f nil)
                         ((m x) r)
                         ((n y) nil)
                         (o nil)
                         (p nil)
                         (q nil)))

(defun siblings (person family)
  "Return a list of PERSON's siblings."
  (remove person (cdr (find person family :key #'cdr :test #'member))))

(defun siblingsp (person1 person2 family)
  "Are PERSON1 and PERSON2 siblings?"
  (find person2 (siblings person1 family)))

(defun parents (person family)
  "Return a list of PERSON's parents."
  (car (find person family :key #'cdr :test #'member)))

(defun parentp (parent child family)
  "Is PARENT a parent of CHILD?"
  (find parent (parents child family)))

Try it:

CL-USER> (siblings 'p *family*)
(Q)
CL-USER> (siblingsp 'q 'p *family*)
P
CL-USER> (parents 'p *family*)
(E W)

Now, to find the grandparents for example, you just have to understand what grandparents are: (A list of) The parents of both parents. Then, ask yourself how it is for grandchildren. Finally, the spouse function should be rather easy, given this example.