Am Mittwoch, 15. Oktober 2008 00:34 schrieb Derek Elkins:
It's not technically true. Type classes and interfaces a la Java are very fundamentally different neither is remotely capable of doing what the other does.
Could you elaborate on that, please? I always understood Java's interfaces to be somewhat similar to type classes (and I learnt the bit of Java I know before I even knew the term "Functional Programming", never really got the whole OO thing though). An interface, I thought, is a contract stating that the classes implementing that interface provide certain operations (obeying some rules). If there's more to interfaces, I'm happily unaware of that :) In what way is that "very fundamentally different" from type classes? As the languages as a whole are fundamentally different, that similarity is of course rather superficial, so I will not say that stressing it is beneficial, but I'm not convinced it is detrimental either.
I strongly agree with the thrust of your email. This "type classes are kinda like interfaces" meme is horrible.
Because of the tendency to confuse OO programmers learning Haskell, or is there a deeper reason? (Answer to this question could be superfluous after addressing the above)
For example, this is a line from RWH: "Typeclasses may look like the objects of object-oriented programming, but they are truly quite different." Also later there is another sidebar along those lines.
Now that is something I wouldn't have dreamt of. If anything, I would relate objects to values (except that objects tend to be mutable). Thanks, Daniel