abstract exception handler/logger into its own file

shell/update-thread.sml

@@ -2,7 +2,6 @@ structure UpdateThread =
 struct
   open CML
   open MailboxType
-  open InputMsg
 
   fun sendMsg (msg, drawMailbox) =
     case msg of DRAW msg => Mailbox.send (drawMailbox, msg)
@@ -15,46 +14,12 @@ struct
         end
     | [] => ()
 
-  val textCommands = ref ""
-
-  fun addTextCommand inputMsg =
-    case inputMsg of
-      CHAR_EVENT chr =>
-        let
-          val chr = CharVector.fromList [chr]
-          val newInput = !textCommands ^ chr
-        in
-          textCommands := newInput
-        end
-    | _ => ()
-
-  fun handleException e =
-    let
-      (* print stack trace for debugging purposes, 
-       * and then raise another exception to exit the program *)
-      val stackTrace = MLton.Exn.history e
-      val stackTrace = String.concatWith "\n" stackTrace
-      val () = print "ERROR:\n"
-      val () = print (stackTrace ^ "\n\n")
-
-      val history = !textCommands ^ "\n\n"
-      val () = print ("HISTORY: " ^ history)
-
-      val textOutput = stackTrace ^ "\n" ^ history
-
-      val io = TextIO.openAppend "exceptions.log"
-      val () = TextIO.output (io, textOutput)
-      val () = TextIO.closeOut io
-    in
-      raise Empty
-    end
-
   fun loop (app: AppType.app_type, inputMailbox, drawMailbox) =
     let
       val inputMsg = Mailbox.recv inputMailbox
-      val () = addTextCommand inputMsg
+      val () = ExceptionLogger.addCommand inputMsg
 
-      val app = AppUpdate.update (app, inputMsg) handle e => handleException e
+      val app = AppUpdate.update (app, inputMsg) handle e => ExceptionLogger.log e
 
       val () = sendMsgs (#msgs app, drawMailbox)
     in