type t = string

let is_lower c = c >= 'a' && c <= 'z'

let is_body c =
  is_lower c || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c = '_'

let well_formed s =
  String.length s > 0
  && is_lower s.[0]
  && String.for_all is_body s

let of_string s = if well_formed s then Ok s else Error (`Invalid_label s)
let to_string t = t
let equal = String.equal
let compare = String.compare
let pp fmt t = Format.fprintf fmt "%s:" t

module Map = Map.Make (String)