[bdj]

The question isn't whether or not feature A can be implemented in language X, it is whether or not it has to be implemented as a local or global transformation. This is what the paper cited above defines as expressibility: adding a feature that requires a global transformation increases expressibility.

I made no claims about whether or not more or less expressibility is a good thing or how it relates to productivity. Nothing in my responses has anything to do with whether or not functional or imperative styles are better in terms of productivity or maintainability. In fact, by the definition in the paper, adding imperative features to a functional language increases expressibility. Also, adding goto to a language increases expressibility, so it is not a metric that is solely related to maintainability and productivity.

I am not arguing that Xtend is a bad idea at all, in fact I think it's a great idea. The whole reason people like languages with powerful macro systems is that they can implement features that Xtend gives to Java in the language itself, rather than having to wait for a new language implementation.