type tree = B of tree | W of tree | Dec of tree * tree | Leaf;;
 
let rec gen w b = match (w,b) with
| (0,0) -> Some Leaf
| (w,b) when (w < 0 || b < 0) -> None
| (w,b) ->
        let l = gen (w-1) b in
        let r = (
                if w = 0 then
                        (if b = 1 then Some Leaf
                        else None)
                else match gen (w-1) (b-1) with
                | None -> None
                | Some x -> Some (W x)) in
        match (l,r) with
        | (None, None) -> None
        | (Some x, None) -> Some (W x)
        | (None, Some x) -> Some (B x)
        | (Some x, Some y) -> Some (Dec (x, y));;
               
 
let rec prof s = function
| B a -> prof ('B'::s) a
| W b -> prof ('W'::s) b
| Dec (a,b) -> (prof ('W'::s) a) @ (prof ('B'::s) b)
| Leaf -> [s]
       
 
let a = gen 5 3;;
let l = (function Some x -> x) a;;
let nbr = List.length (prof [] l);;