(* Define auxiliary procedures *)
let proc traverse(t) =
    if isEmptyTree(t)
    then unit
    else if isLeaf(t)
    then write leafVal(t)
    else let left := leftSubtree(t) in
         let right := rightSubtree(t) in
             traverse(left);
             write nodeVal(t);
             traverse(right)
in

let exampleTree := node(4, node(2, leaf(1), leaf(3)),
                           node(6, leaf(5), leaf(7)))
in
let exampleLeaf := leaf(9) in
let exampleNull := null
in
  (try (if isEmptyTree(exampleTree) then write 0 else write 1)); (* 2 pt *)
  (try (if isEmptyTree(exampleNull) then write 0 else write 1)); (* 2 pt *)
  (try (if isLeaf(exampleTree) then write 0 else write 1));      (* 2 pt *)
  (try (if isLeaf(exampleLeaf) then write 0 else write 1));      (* 2 pt *)
  (try (write nodeVal(exampleTree)));                            (* 2 pt *)
  (try (write leafVal(exampleLeaf)));                            (* 2 pt *)
  (try (write nodeVal(leftSubtree(exampleTree))));               (* 2 pt *)
  (try (write nodeVal(rightSubtree(exampleTree))));              (* 2 pt *)
  (try (write leafVal(leftSubtree(rightSubtree(exampleTree))))); (* 2 pt *)
  (try (traverse(exampleTree)));                                 (* 2 pt *)
  (try (traverse(mirrorize(exampleTree))))                       (* 10 pt *)