Paste: ocaml parsey thing

open Astring
open Rresult

type os_t = Darwin | FreeBSD | OpenBSD | Linux

type version_t = {
    major : int;
    minor : int;
    extra : string;
  }

type t = {
    os : os_t;
    version : version_t;
    hostname : string;
    uuid : Uuidm.t;
  }


let os_of_string = function
  | "Darwin" -> Darwin
  | "FreeBSD" -> FreeBSD
  | "OpenBSD" -> OpenBSD
  | "Linux" -> Linux
  | _ -> die "Unknown operating system"

let string_of_os = function
  | Darwin -> "Darwin"
  | FreeBSD -> "FreeBSD"
  | OpenBSD -> "OpenBSD"
  | Linux -> "Linux"

let string_of_version v = Printf.sprintf "%d.%d%s" v.major v.minor v.extra

type extra_behavior = NoExtra | SeparateWith of char

let version_of_os_string =
  let parse_into_version extra str =
    let open String in
    match cuts "." str with
    | major :: fld2 :: tail -> (
      let major = int_of_string major in
      match extra with
      | NoExtra -> {major=major;
                    minor=int_of_string fld2;
                    extra=""}
      | SeparateWith(extra_separator) ->
         if extra_separator = '.' then
           let minor = int_of_string fld2 and
               extra = "." ^ concat ~sep:"." tail
           in {major; minor; extra}
         else
           let separator_string = of_char extra_separator in
           match cuts (of_char extra_separator) fld2 with
           | minor :: rs ->
              {major=major;
               minor=int_of_string minor;
               extra=separator_string ^ concat ~sep:separator_string rs}
           | _ -> die "Unable to parse minor component of version")
    | _ -> die "Unable to parse major component of version"
    in function
        | OpenBSD -> parse_into_version NoExtra
        | Linux | Darwin -> parse_into_version (SeparateWith('.'))
        | FreeBSD -> parse_into_version (SeparateWith('-'))