As another example, it would be nice to be able to “premix” traits that are commonly used together without creating a new trait:

type AB = A with B
new AB { } // doesn't work

Instead of having to always expand it out everywhere. Furthermore, it is just strange that with does not associate:

new A with B with C { } // okay
new A with (B with C) { } // doesn't work
new (A with B) with C { } // doesn't work
new (A with B) { } // doesn't work

I think Martin has said he would at least commit to fixing the associativity issue, but we’ll see whether it can be relaxed further.

e.g. (this is obviously silly, but…)
type Nat = {…}

abstract class MyPartialNat extends Nat {
type T = int
val z = 0
}

object MyNat extends MyPartialNat {
def s(arg:Int) = arg + 1
}

object MyWeirdNat extends MyPartialNat {
def s(arg:Int) = arg - 1
}

could translate into

type Nat {…}

trait Nat$Trait {…} // compiler generated trait

abstract class MyParitalNat extends AnyRef with Nat$Trait {
…

@James: It probably just seemed more natural to me as I am used to thinking about these things in terms of Featherweight Scala which only has traits. It is reasonable to think of objects as modules that have not been ascribed a signature. For example, I could have written my example above like:

scala> type Nat = { type T; val z: T; def s(arg: T): T }
defined type alias Nat

scala> object MyNat {
     |   type T = Int
     |   val z = 0
     |   def s(arg: Int) = arg + 1
     | }
defined module MyNat

scala> val opaqueNat : Nat = MyNat
opaqueNat: Nat = MyNat$@ec8f6e

or

object MyNat extends AnyRef with Nat {…

I don’t know why I hadn’t considered just val MyNat = new Nat {…

I think it’s because I wanted a top level construct.

BTW, I have a GeSHi definition file for SML if you want it. I wrote it for my blog originally, so I didn’t bother putting colors into the PHP (it’s dependent on CSS and/or a hacky modification of geshi.php), but it wouldn’t be too hard to modify to work with a conventional WP-Syntax setup..