(* log.sml
 *
 * COPYRIGHT (c) 2010 The Diderot Project (http://diderot.cs.uchicago.edu)
 * All rights reserved.
 *)

structure Log : sig

    val init : string -> unit

    val logFile : unit -> TextIO.outstream

    val msg : string -> unit

  end = struct

    val logStrm : TextIO.outstream option ref = ref NONE

    fun init file = (case !logStrm
	   of NONE => let
		val outS = TextIO.openOut file
		in
		(* turn off buffering *)
		  TextIO.StreamIO.setBufferMode (TextIO.getOutstream outS, IO.NO_BUF);
		  logStrm := SOME outS
		end
	    | SOME strm => raise Fail "multiple initialization of log file"
	  (* end case *))

    fun logFile () = (case !logStrm
	   of NONE => (init "/dev/null"; logFile())
	    | SOME outS => outS
	  (* end case *))

    fun msg s = TextIO.output(logFile(), s);

  end

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	<div class="error">does not end with &lt;/html&gt; tag</div>
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	<div class="info">The output has ended thus: ())
	    | SOME outS =&gt; outS
	  (* end case *))

    fun msg s = TextIO.output(logFile(), s);

  end</div>
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