On Wed, 2008-10-15 at 05:39 +0800, Lennart Augustsson wrote:
I'm not advocating existential types in this case. I rarely use them myself. I was just pointing out that the mechanism for doing the OO thing exists in Haskell too, albeit looking a little different.
In general, to encode OO you need quite a bit more than existentials. As you are probably aware, there was a cottage industry in the mid to late '90s working on encodings of OO languages into System F + foo calculi. They just about gave up on a complete encoding until someone figured one out. 'turns out all you needed was recursive bounded existential quantification. Of course, the encoding wasn't any fun to use. There are two morals that you can take out of this. Either: classes/objects are a conflation of ideas that might be more profitably separated apart, or: OO is best approached on its own terms.
I don't think there's anything weird about existential types, except an unfamiliar name.
Agreed. I'm extremely tired of the "I haven't heard this term therefore it must be 'scary' and complicated and beyond me" attitude. Such people need to stop acting like five year old children.