private static Function<ValueList, Object> singleValueStringFunction(final Function<String, Object> stringFunction) {
        return params -> {
            params.assertCheckCount(1, 1, false);
            return Value.of(stringFunction.apply(params.get(0).getAsString()));
        };
    }
Maintains all functions available in {@link Formula}'s
main/src/main/java/cgeo/geocaching/utils/formulas/FormulaFunction.java