I think you mean typeclasses?
One of the things that always bothered me about interfaces was the inability to define a default implementation, especially when developing UIs. A proper mixin system (like what's used by React's components) has solved this particular problem for me.
Fixed. Thanks.
I agree with you about Haskell. I almost went into a discussion of how Rust does this. They don't have subtypes, but they do have code reuse if you explicitly declare it. Caution, I'm just an admirer of Rust, not a user. So maybe it sucks too, but this seems closer to how things ought to be.
http://static.rust-lang.org/doc/master/tutorial.html#default...
https://mail.mozilla.org/pipermail/rust-dev/2014-March/00895...