Question

I’m wrote a function that finds the height of a binary tree (i.e. the # of nodes along the longest path from the root to the leaf).

let rec height (t: 'a tree) : int =
begin match t with
| Empty -> 0
| Node (l, v, r) -> 1 + max (height 1) (height r)
end

I believe that my function is correct, but the syntax error that occurs when I run my test says “this function is applied to too many arguments; maybe you forgot a ‘;’.

This is my test case

let test () : bool =
height Node(Node(Empty, 1, Empty), 3, Node(Empty, 2, Node(Empty, 4, Empty))) = 3
;; run_test "Node(Node(Empty, 1, Empty), 3, Node(Empty, 2, Node(Empty, 4, Empty)))" test

What is wrong with my test case?

Thanks!

Answer 1

Consider the expression

height Node (Empty, 0, Empty)

In OCaml, adjacent values indicate function application, which is left-associative. So this is the same as:

(height Node) (Empty, 0, Empty)

The following will work:

height (Node (Empty, 0, Empty))

In other words, you just need to add parentheses.