a.cpp

inline
Text Volume::labelTextFmt( bool doing, has_label ) const {
    if (doing && !has_label) return _("Clearing label on %1$s")
    if (doing && has_label)  return _("Setting label on %1$s to %2$s")
    if (!has_label)          return _("Clear label on %1$s")
    else                     return _("Set label on %1$s to %2$s")
}

Text Volume::labelText( bool doing ) const {
    return  sformat(labelTextFmt(doing, !label.empty()), dev.c_str(), label.c_str());
}

a.hs

labelText doing = sformat (labelTextFmt doing $ empty label) [dev, label]
  where
    labelTextFmt True False  = _("Clearing label on %1$s")
    labelTextFmt True True   = _("Setting label on %1$s to %2$s")
    labeltextFmt False False = _("Clear label on %1$s")
    labelTextFmt False True  = _("Set label on %1$s to %2$s")