Of course I have never programmed in Haskell, so perhaps I am showing my ignorance, but my impression of Haskell is that it has all of the type restrictions of java plus many, many more. My point is that a language like Haskell (or Java, take your pick), can still have easy to use libraries written for it.

Sure, you can't change the methods of a class has at run time. Who cares? Like I said you can just create an object wrapper, sometimes called a decorator if you are into design patterns, that has all of the methods of the original object plus a few more (or even a few less, doesn't matter). This gives you all of the functions of the original object plus more, just like modifying a class at runtime does. Possible in Java, possible in Haskell, possible even in JavaScript.

The only difference is that you have to explicitly call into the wrapper classes. You can't expect objects that you instantiate from outside your library to have these methods.

But again, who cares. If you want to use the cool new library functions, use them. Otherwise don't.

Specific example: if we are talking about jquery, you can't expect document.GetElementById('foo') to have special jquery functions. But you can expect $('#foo') to have them, which is the same thing so you really have nothing to complain about.