On 8/18/06, John Meacham
There is a major difference though, in C++ (or java, or sather, or c#, etc..) the dictionary is always attached to the value, the actual class data type you pass around. in haskell, the dictionary is passed separately and the appropriae one is infered by the type system. C++ doesn't infer, it just assumes everything will be carying around its dictionary with it.
C++ programmers deal with this using a number of techniques, mostly involving templates. Actually, there is one technique using C++ templates that I really want to see going mainstream in the Haskell implementations. Existential types are already there, now I want to see associated types (trait types in C++). Maybe I've been doing too much C++ programming in the last few years, but a lot of the times when I end up using multiparameter type classes, what I really want is an associated type. For example class Monad s => Store s where type Key insert :: Binary -> s Key retrStore :: Key -> s Binary ... so that part of the instance is a choice of the key type. For those who are interested, I'm sure the relevant papers are readily available on citeseer/Google. :-) Tom