Joel

module BinaryTree =
    type Tree<'T when 'T : comparison> =
        | Empty
        | Leaf of 'T
        | Node of Tree<'T> * 'T * Tree<'T>

    let leaf value =
        let l = Leaf(value)
        l

    let buildTree subT1 subT2 value =
        let tree = Node(subT1, value, subT2)
        tree

    let isLeaf item =
        match item with
        | Empty -> false
        | Leaf -> true
        | Node -> false

    let head tree =
        match tree with
        | Empty -> failwith "Empty tree"
        | Leaf(i) -> i
        | Node(l, v, r) -> v

    let left tree =
        match tree with
        | Empty -> failwith "Empty tree"
        | Leaf -> failwith "Argument can't be a leaf"
        | Node(l, v, r) -> l

    let right tree =
        match tree with
        | Empty -> failwith "Empty tree"
        | Leaf -> failwith "Argument can't be a leaf"
        | Node(l, v, r) -> r

    let empty =
        let t = Empty
        t

    let isEmpty tree =
        match tree with
        | Empty -> true
        | _ -> false