Hex.Digit
type t =
| H0
| H1
| H2
| H3
| H4
| H5
| H6
| H7
| H8
| H9
| H10
| H11
| H12
| H13
| H14
| H15
val of_char_exn : Core_kernel.Char.t -> t
val to_int : t -> int