Tree Equality

It often is necessary to test whether two trees are equal, even though they are in different memory locations. We will say two trees are equal if:

• the structures of the trees are the same

• the leaf nodes are equal

(defn equal [x y]
  (if (cons? x)
      (and (cons? y)
           (equal (first x) (first y))
           (equal (rest x) (rest y)))
      (= x y) ))

>(equal '(+ a (* b c)) '(+ a (* b c)))

true

Some say that two trees are equal if they print the same.

Note that this function treats a cons as a binary first-rest tree rather than as a lhs-rhs tree.