foncteur.ml

exception Error of string

type 'a node =
        | Cons of { current: 'a; next: 'a node }
        | Nil

module Node = struct
        let empty = Nil

        let add a b = Cons { current = a; next = b }
end
type 'a truc = { cmp: ('a -> 'a -> bool); head: 'a node }

module Truc = struct
        (* create an empty truc *)
        let empty (cmp: 'a -> 'a -> bool): 'a truc = { cmp = cmp; head = Node.empty }

        (* add a machin to a truc *)
        let add (machin: 'a) (truc: 'a truc) =
                {
                        cmp = truc.cmp;
                        head = Node.add machin truc.head
                }

        (* return the position of the machin in the truc *)
        let position (machin: 'a) (truc: 'a truc) =
                let rec aux idx node =
                        match node with
                        | Cons { current = head; next = _ } when truc.cmp machin head -> idx
                        | Cons { next = tail; _ } -> aux (idx + 1) tail
                        | Nil -> raise (Error "Element does not exist in the truc")
                in
                aux 0 truc.head
end

let my_truc = Truc.empty (=)
                        |> Truc.add 5
                        |> Truc.add 4
                        |> Truc.add 3
                        |> Truc.add 2
                        |> Truc.add 1
        ;;

Printf.printf "The position of 4 is %d\n" (my_truc |> Truc.position 4)