use concurrency for rebuilding search list after deletion so we don't block main thread on very, very large files

shell/search-thread.sml

@@ -0,0 +1,14 @@
+structure SearchThread =
+struct
+  open CML
+
+  (* Prerequisite to sending message: move buffer to end. *)
+  fun loop (searchMailbox, inputMailbox) =
+    let
+      val (buffer, searchString) = Mailbox.recv searchMailbox
+      val (_, searchList) = SearchList.build (buffer, searchString)
+      val () = Mailbox.send (inputMailbox, InputMsg.WITH_SEARCH_LIST searchList)
+    in
+      loop (searchMailbox, inputMailbox)
+    end
+end