Hi
As it would operate on types rather than values (think sizeOf), the result for "[a]" would probably be "(1, Nothing)" - a list takes one byte at minimum and infinite bytes at maximum.
That interface seems horrible - it looks like it will only be useful to a small number of people, and not be general at all. I really don't like the idea of an interface specifying a "fuzz factor" (which is what upper/lower bounds correspond to) In my BinaryDefer library I have a class BinaryDeferStatic: class BinaryDefer a => BinaryDeferStatic a where -- | Must be a constant, must not examine first argument getSize :: Proxy a -> Int This is for things which have a fixed and static size based on their type. I could also see a reason for having a sizeOf method in the Binary class - where if unimplemented it just calls encode and then B.length. Anything else just seems to be an ugly API... Thanks Neil