That feeling when you realize there's no magic in Cmdliner

cmdliner_term_v1.ml

(*
  Sample command-line argument specified using Cmdliner's author's style.
*)

open Cmdliner

let seed_term =
  let doc = "
    Use the number $(docv) to initialize the global pseudo-random number
    generator.
"
  in
  Arg.(value & opt (some int) None & info ["seed"] ~docv:"SEED" ~doc)

cmdliner_term_v2.ml

(*
  Same command-line argument specification rewritten using a plain style.
*)

open Cmdliner

let seed_term =
  let doc = "
    Use the number $(docv) to initialize the global pseudo-random number
    generator.
"
  in
  let info = Arg.info ["seed"] ~docv:"SEED" ~doc in
  let arg = Arg.opt (Arg.some Arg.int) None info in
  Arg.value arg