On Wed, 30 Apr 2003 at 19:35 GMT, Dave Thomas wrote: > Remember: objects equal data + operations. Two objects have different > types if they differ in either. True (my OO-hat is a little dusty ...). > Also remember, their may be a subclassing or delegation interface > between the mutable and immutable interfaces; there's nothing to say > that you have to duplicate information. Yes, now I see what it could be like (using either subclassing or delegation). Thanks. Just out of curiosity: would you comment on the two alternative designs I mentioned in my previous reply ? (It is rather appropriate that the LotY should be Haskel.) Greetings, Simon PS: Since this is our first mail exchange I figure I am entitled to a short I-read-your-books-and-loved-them-,-thanks-for-everything statement :) -- There are 10 types of people in the world... those who understand binary and those who don't.