log exceptions that occur to a local file

.gitignore

@@ -1,2 +1,3 @@
 shf
 shf-tests
+exceptions.log

shell/gl-draw.sml

@@ -229,9 +229,7 @@ struct
     end
 
   fun yank (shellState: t, str) =
-    ( Glfw.setClipboardString (#window shellState, str);
-      shellState
-    )
+    (Glfw.setClipboardString (#window shellState, str); shellState)
 
   fun consumeDrawEvent (shellState, msg) =
     let

shell/update-thread.sml

@@ -2,6 +2,7 @@ structure UpdateThread =
 struct
   open CML
   open MailboxType
+  open InputMsg
 
   fun sendMsg (msg, drawMailbox) =
     case msg of DRAW msg => Mailbox.send (drawMailbox, msg)
@@ -14,21 +15,46 @@ 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 app = 
-        AppUpdate.update (app, inputMsg) 
-          handle 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 (stackTrace ^ "\n")
-            in
-              raise Empty
-            end
+      val () = addTextCommand inputMsg
+
+      val app = AppUpdate.update (app, inputMsg) handle e => handleException e
 
       val () = sendMsgs (#msgs app, drawMailbox)
     in