99 problems - python - 54A

Check whether a given term represents a binary tree

In Prolog or Lisp, one writes a predicate to do this.

Example in Lisp:

* (istree (a (b nil nil) nil))
T
* (istree (a (b nil nil)))
NIL
def is_tree(t):
    if t == None:
        return True
    elif type(t) == tuple and len(t) == 3:
        (val, left, right) = t
        return is_tree(left) and is_tree(right)
    return False

Is using lispy tuple for representing tree cheating?