fun addExpanded(failingResult: FailingResult) {
        when (failingResult) {
            is SingleFailureResult -> add(failingResult)
            is MultipleFailuresResult -> failingResult.failures.forEach(::addExpanded)
        }
    }

    fun collectFrom(current: LanguageTreeElement) {
        when (current) {
            is ErroneousStatement -> addExpanded(current.failingResult)