Lambda the Ultimate

Most of the new features that are interesting from a language design perspective were discussed here in the past. These include generics, autoboxing/unboxing, metadata and typesafe enums. We also discussed some of the new libraries and APIs.

I can understand how Gosling is feeling right now: I wouldn't feel comfortable being responsible for a language without generics...

What's next for Java? The new release model is explained here. The general design philosophy here.

I believe there was a conversation on LtU once (perhaps LtU1?) where someone was explaining World-passing style in Clean (I think it was Clean), and explained that there was some syntax for making the World-passing implicit, so that it'll just automatically thread it through for you. I've searched the archives for a while to no avail. Does anyone remember the conversation I'm referring to?

Simon Peyton-Jones, via Haskell-list:

I've finished my first attempt at implementing Generalised Algebraic
Data types in GHC. Ordinary algebraic data types are generalised to
allow you to write an explicit type signature for each constructor; for
example:

     data Term a where
	Lit :: Int -> Term Int
	Succ :: Term Int -> Term Int
	IsZero :: Term Int -> Term Bool	
	If :: Term Bool -> Term a -> Term a -> Term a

Notice that some of these constructors have return types that are not
just "Term a"... that's the whole point! Now you can write typed
evaluator for these terms:

    eval :: Term a -> a
    eval (Lit i)		= i
    eval (Succ t) 	= 1 + eval t
    eval (IsZero i) 	= eval i == 0
    eval (If b e1 e2)	= if eval b then eval e1 else eval e2

This is implementation of the "wobbly types" we've discussed before in GHC, slated for release in version 6.4. Simon also give a pointer to Tim Sheard's site, as he's done a lot of related work. There I found an interesting looking paper on Omega, a language which takes the GADT idea even further.

If so you might be interested in the paper The Security Architecture of qmail by M. Hafiz, R. Johnson, R. Afandi, PLoP2004.