Roman numerals. Implementation employs Nathan Mishra Linger's Roman module, but an improved interface is provided here. Also, zero is deliberately not supported.
module Biocaml_romanNum: sigtype 
exception Bad of string
val of_string_exn : string -> tof_string but raise Bad if unable to parse string.val of_int_exn : int -> tof_int but raise Bad if unable to convert integer.end