signature MLTON_IO =
   sig
      type instream
      type outstream

      val inFd: instream -> Posix.IO.file_desc
      val mkstemp: string -> string * outstream
      val mkstemps: {prefix: string, suffix: string} -> string * outstream
      val newIn: Posix.IO.file_desc * string -> instream
      val newOut: Posix.IO.file_desc * string -> outstream
      val outFd: outstream -> Posix.IO.file_desc
      val tempPrefix: string -> string
   end

• inFd ins
  returns the file descriptor corresponding to ins.

• mkstemp s
  like the C mkstemp function, generates and open a temporary file with prefix s.

• mkstemps {prefix, suffix} 
  like mkstemp, except it has both a prefix and suffix.

• newIn (fd, name)
  creates a new instream from file descriptor fd, with name used in any Io exceptions later raised.

• newOut (fd, name)
  creates a new outstream from file descriptor fd, with name used in any Io exceptions later raised.

• outFd out
  returns the file descriptor corresponding to out.

• tempPrefix s
  adds a suitable system or user specific prefix (directory) for temp files.