O'Caml

Good day, fellow /prog/raiders.
I am currently learning O'Caml, what should I pay attention? What is Bad and what is Good on this language?

let rec extended_gcd a b =
    if a > b then extended_gcd b a
    else
        if b = 0 then (1, 0)
        else
            let qr = divide a b;
            let st = extended_gcd b (snd qr);
            (snd st, (fun s q t -> s - q * t) (fst st) (fst qr) (snd st));;

All I receive is a sintax error. Where is this error?