1signature TextIO = 2sig 3 type instream 4 type outstream 5 val stdOut : outstream 6 val stdErr : outstream 7 val openIn : string -> instream 8 val closeIn : instream -> unit 9 10 val inputLine : instream -> string option 11 val output : outstream * string -> unit 12end 13 14 15structure TextIO :> TextIO = 16struct 17 open TextIO 18 fun inputLine s = 19 case TextIO.inputLine s of 20 "" => NONE 21 | s => SOME s 22end 23