let read_file name =
    let ic = open_in name in
    let try_read () =
        try Some (input_line ic)
        with End_of_file -> None in
    let rec aux acc =
        match try_read () with
        | Some s -> aux (s::acc)
        | None -> close_in ic; acc in
    aux []

module CS = Set.Make(Char);;

let set_of_string str =
    let rec aux s i st =
        if i < 0 then st
        else aux s (i - 1) (CS.add s.[i] st) in
    aux str ((String.length str) - 1) CS.empty

let map_pair f (a, b) = (f a, f b)

let curry f x y = f (x, y)
let uncurry f (x, y) = f x y
let uncurry3 f (x, y, z) = f x y z

let swap x y = y x