print stack trace for when an exception occurs

Makefile

@@ -1,3 +1,6 @@
+run_debug:
+	./build-unix-debug.sh && ./shf
+
 run:
 	./build-unix.sh && ./shf
 

build-unix-debug.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+mlton -const 'Exn.keepHistory true' -link-opt "$(pkg-config --cflags glfw3) $(pkg-config --static --libs glfw3)" \
+  -export-header ffi/export.h \
+  shf.mlb \
+  ffi/glad.c \
+  ffi/glfw-export.c \
+  ffi/gles3-export.c \
+  ffi/glfw-input.c

shell/update-thread.sml

@@ -17,7 +17,19 @@ struct
   fun loop (app: AppType.app_type, inputMailbox, drawMailbox) =
     let
       val inputMsg = Mailbox.recv inputMailbox
-      val app = AppUpdate.update (app, inputMsg)
+      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 () = sendMsgs (#msgs app, drawMailbox)
     in
       loop (app, inputMailbox, drawMailbox)