open Tk

let rec gcd n m = 
    if n = 0 then
        m
    else if n >= m then
        gcd (n-m) m
    else
        gcd m n;;

let compute entry_n entry_m label_r = 
    fun() -> 
        let n = int_of_string (Entry.get entry_n) in
        let m = int_of_string (Entry.get entry_m) in
        let result = gcd n m in
        Label.configure label_r ~text:(string_of_int result);;

let root = openTk() in
let top_frame = Frame.create root in
let gcd_begin = Label.create top_frame ~text:"gcd(" in
let n = Entry.create top_frame ~width:4 ~relief:`Sunken in
let m = Entry.create top_frame ~width:4 ~relief:`Sunken in
let gcd_end = Label.create top_frame ~text:")=" in
let result = Label.create top_frame in
let button = Button.create root 
                ~text: "Compute"
                ~command: (compute n m result) in
pack [top_frame] ~side:`Top ~expand:true ~fill:`Both ;
pack [gcd_begin] ~side:`Left ~anchor:`E ;
pack [n; m] ~side:`Left ~expand:true ~fill:`X ;
pack [gcd_end; result] ~side:`Left ~anchor:`W ;
pack [button] ~side:`Bottom ~expand:true ~fill:`X ;
mainLoop();;