diff --git a/dsc b/dsc
new file mode 100755
index 0000000..e5703e8
Binary files /dev/null and b/dsc differ
diff --git a/imperative-shell/init-glfw.sml b/imperative-shell/init-glfw.sml
index 3d0b27f..7c7fbe9 100644
--- a/imperative-shell/init-glfw.sml
+++ b/imperative-shell/init-glfw.sml
@@ -59,5 +59,6 @@ struct
       ()
     end
 
-  fun main () = RunCML.doit (init, NONE)
+  fun main () =
+    (RunCML.doit (init, NONE); ())
 end
diff --git a/imperative-shell/shell.sml b/imperative-shell/shell.sml
index 1ed32c9..af2fcfa 100644
--- a/imperative-shell/shell.sml
+++ b/imperative-shell/shell.sml
@@ -1,6 +1,16 @@
 structure Shell =
 struct
-  fun main () = InitGlfw.main ()
+  fun main () =
+    case CommandLine.arguments () of
+      ["-r"] => (print "todo: convert dsc files to sml file\n")
+    | [] => InitGlfw.main ()
+    | args =>
+        let
+          val args = String.concatWith "" args
+          val msg = String.concat ["unknown arguments error: \"", args, "\"\n"]
+        in
+          print msg
+        end
 end
 
 val _ = Shell.main ()