done with scaffolding for file mailbox; next, send message to file mailbox to export and import, and handle these messages properly from the file mailbox

imperative-shell/file-thread.sml

@@ -0,0 +1,20 @@
+signature FILE_THREAD =
+sig
+  val run: FileMessage.t Mailbox.mbox -> unit
+end
+
+structure FileThread :> FILE_THREAD =
+struct
+  open FileMessage
+
+  fun run fileMailbox =
+    let
+      val _ =
+        case Mailbox.recv fileMailbox of
+          SAVE_TRIANGLES triangles => ()
+        | EXPORT_TRIANGLES triangles => ()
+        | IMPORT_TRIANGLES => ()
+    in
+      run fileMailbox
+    end
+end