Dictionary using closures in OCaml

lookup.ml

let empty key = None

let put key value lookup = 
  (fun k -> if (k = key) then Some value else (lookup k))

(* use *)

let (|>) x f = f x

let lookup = empty |> put "a" 1 |> put "b" 2 |> put "c" 3;;

["a"; "b"; "c"; "d"] |> List.map lookup |> List.iter (function Some i -> Printf.printf "%d\n" i | None -> print_endline "None")