[bdj]

Closures are code+data and objects are also code+data, so adding closures to a language with an object system does not increase expressibility.

The main difference is that with closures you write the code and the data part (the environment) is captured implicitly, whereas with objects, both the code and data are explicit. This makes it possible to convert a closure into an object, and an object into a closure, without having to change the whole program.

It is a little more difficult to go from closures to objects because you have to find the free variables and make them explicit, but it still isn't a global transformation. If you want to see how to implement objects with closures, check out SICP.

[buff-a]

It's all code plus data. I can implement any java, C#, Xtend feature in C or assembly language, but by your argument that makes C# no more expressive then C.

If this is your argument, then it would appear that your argument is that the entire class of imperative languages are a waste of time and we should all be using lisp or scala.

Back in the real world, I find C# to be more productive than C, because I am able to express myself more succinctly. Xtend seems to do that for java. In the imperative world, your definition of expressibility is insufficient to determine increases in productivity.

[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.