abstract exception handler/logger into its own file

shell/exception-logger.sml

@@ -0,0 +1,38 @@
+structure ExceptionLogger =
+struct
+  open InputMsg
+
+  val textCommands = ref ""
+
+  fun addCommand inputMsg =
+    case inputMsg of
+      CHAR_EVENT chr =>
+        let
+          val chr = CharVector.fromList [chr]
+          val newInput = !textCommands ^ chr
+        in
+          textCommands := newInput
+        end
+    | _ => ()
+
+  fun log 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
+end