public Value getValue() {
        try {
            if (formula == null) {
                ensureFormula();
            }
            return formula == null ? null : formula.evaluate(varList == null ? x -> null : varList::getValue);
        } catch (FormulaException fe) {
            return null;
        }
    }
Allows live-editing of a formula, optionally associated with a Variable List
main/src/main/java/cgeo/geocaching/ui/FormulaEditText.java