public static String rootDirectoryPrefix(String file) {
    { String extension = Stella.fileExtension(file);

      if (Stella.stringEqlP(extension, ".ste")) {
        return (Stella.rootSourceDirectory());
      }
      else if (Stella.stringEqlP(extension, ".lisp") ||
          (Stella.stringEqlP(extension, ".java") ||
           (Stella.stringEqlP(extension, ".cc") ||
            Stella.stringEqlP(extension, ".hh")))) {
        return (Stella.rootNativeDirectory());
      }
      else {
        return (Stella.rootNativeDirectory());
      }
    }
  }