On 10/11/06, Bulat Ziganshin wrote:

it's a sort of problem that bites me many times when i start to wrote Streams library :) although you said that you discovered the dictionaries mechanism, i propose you to read http://haskell.org/haskellwiki/OOP_vs_type_classes page where you can find something that you don't yet know

Yes, I did actually know this stuff, it was just paged out, and I posted before thinking. :-) Something to do with having two small kids, one of whom gets up waaaaay too early in the morning (i.e. 5 - 5:30am). :-) In theory, however, there is no particular reason why a runtime type cast couldn't be implemented to allow downcasting, but it does require the runtime system to have a repository of instance declarations, or associate with static data for a type the classes of which it is an instance. It's been a few years, but if my recallection is correct, the Mercury runtime system does this. T.