I can't see how I'd implement the Inputs property without used a List<> or an array as the backing store, so this shouldn't be a problem.

If I need the opposite of IsInInput is there a way to do that other than creating a new expression like below?

case "NotInInput":
    return Expression.Not(Expression.Call(Expression.Constant(rule.Inputs.ToList()),
                            _miListContains.Value,
                            propExpression));

Or maybe add a new boolean field called Negate on Rule class that would invoke Expression.Not if true?

@jamescurran Do you think that this can be merged, do you need anything else from me?

@jamescurran Any update on if this change to support the JSON configuration provider can be merged?