signature STREAM = sig
  type fileId = int
  type fileOffset = int
  type pos = fileId * fileOffset
  type ppos (* pretty pos *)

  type t
  type fileInfo

  val recycle: t -> fileInfo

  val ppos2str: ppos -> string
  val printPos: fileInfo -> pos -> unit

  val getchar: t -> char option * t

  (* Will throw UngetcError, if applied at the beginning of the stream.
   * Can be always avoided, so is not provided in sig file *)
  val ungetc: t -> t

  val getOffset: t -> fileOffset
  val getPos: t -> pos
  val getPosAfterCharRead: t -> pos
  val getPposFromPos: pos -> t -> ppos

  (* Assumed to be called once for given pos, so will throw Unreachable on
   * second call *)
  val pposWithoutCol: ppos -> ppos

  val getSubstr: fileOffset -> fileOffset -> t -> string
  val isFirstOnLine: pos -> t -> bool

  (* throws IO.Io *)
  val streamInit: string -> t
end