signature IMPERATIVE_IO =
sig
  structure StreamIO : STREAM_IO
  type elem = StreamIO.elem
  type instream
  type outstream
  type vector = StreamIO.vector
  val canInput : instream * int -> int option
  val closeIn : instream -> unit
  val closeOut : outstream -> unit
  val endOfStream : instream -> bool
  val flushOut : outstream -> unit
  val getInstream : instream -> StreamIO.instream
  val getOutstream : outstream -> StreamIO.outstream
  val getPosOut : outstream -> StreamIO.out_pos
  val input : instream -> vector
  val input1 : instream -> elem option
  val inputAll : instream -> vector
  val inputN : instream * int -> vector
  val lookahead : instream -> elem option
  val mkInstream : StreamIO.instream -> instream
  val mkOutstream : StreamIO.outstream -> outstream
  val output : outstream * vector -> unit
  val output1 : outstream * elem -> unit
  val setInstream : instream * StreamIO.instream -> unit
  val setOutstream : outstream * StreamIO.outstream -> unit
  val setPosOut : outstream * StreamIO.out_pos -> unit
end