int -> string, converting integers into double-struck unicode characters

mathbb_unicode.ml

(** Conversion between integers and unicode \mathbb strings *)
(* 0-9 as unicode \mathbb{d} multibyte character strings *)
let ustr_bb_digits =
  Array.init 10 (fun i -> Printf.sprintf "\xf0\x9d\x9F%c" (char_of_int (0x98 + i)))

(** Converts an integer into an array of decimal digits *)
let int_to_array i =
  let rec f i acc = if i == 0 then acc else f (i/10) (i mod 10 :: acc) in
  f i []

(** Converts an integer i into a unicode string representation of \mathbb{i} *)
let int_to_bb_ustr i =
  String.concat "" (List.map (fun d -> ustr_bb_digits.(d)) (int_to_array i))

(* Example usage:
# print_string (int_to_bb_ustr 1234567890);;
𝟙𝟚𝟛𝟜𝟝𝟞𝟟𝟠𝟡𝟘
*)