+(defun x-file-dialog (prompt dir default_filename mustmatch only_dir_p)
+"Read file name, prompting with PROMPT in directory DIR.
+Use a file selection dialog. Select DEFAULT-FILENAME in the dialog's file
+selection box, if specified. If MUSTMATCH is non-nil, the returned file
+or directory must exist.
+
+This function is only defined on NS, MS Windows, and X Windows with the
+Motif or Gtk toolkits. With the Motif toolkit, ONLY-DIR-P is ignored.
+Otherwise, if ONLY-DIR-P is non-nil, the user can only select directories."
+ (ns-read-file-name prompt dir mustmatch default_filename only_dir_p))
+