a.cpp

inline
Text Volume::labelTextFmt( bool doing, bool 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")

    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")

a2.cpp

Text Volume::labelText( bool doing ) const {
    Text txt, fmt;

    // compiler should be able to optimize this away I *guess*
    bool has_label = !label.empty()

    if (doing && !has_label)
        fmt = _("Clearing label on %1$s")
    else if(doing && has_label)
        fmt = _("Setting label on %1$s to %2$s")
    else if(!doing && !has_label)
        fmt = _("Clear label on %1$s")
    else
        fmt = _("Set label on %1$s to %2$s")

    return  sformat(fmt, dev.c_str(), label.c_str());
}

funny, a2.cpp ends up having more negation than if it had bool has_no_label.