let bot = !(/rec/ "a" . rec);
let zero = /zero suc/ zero;
let suc n = /zero suc/ suc (n zero suc);

let opt  some = _ : None | some;
let plus iter = !(/plus/ iter . (opt plus));
let star iter = opt (plus iter);

let up_to x n = n bot (/rec/ x . opt rec);

let Pattern_Whitespace = "\t"|"\n"|"\x0B"|"\x0c"|"\r"|" "|"\u{85}"|"\u{200e}"|"\u{200f}"|"\u{2028}"|"\u{2029}";

let oct_digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" ;
let digit     = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9";
let hex_digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" |
                "a" | "b" | "c" | "d" | "e" | "f" |
                "A" | "B" | "C" | "D" | "E" | "F" ;

match
    "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" |
    "i" | "j" | "k" | "l";