Java doesn't have closures. Xtend does. Closures seem to me to satisfy the paper's definition of providing greater expressibility. Certainly, I've done a lot of C# and Java, and having closures in C# has greatly influenced how I write code.
And yet closures appear to be what you claim is a local syntax transform, and therefor can not add any expressibility to the language.
I am confused.
Update: I didnt downvote you btw.
Often, such closures are enough. E.g. with Google Guava's predicates and filter/map methods, you can do with Java (guava + anonymous inner classes) what LINQ enables in C# (System.Linq + lambda expressions). The Java version has a lot more line noise than the C# version, however, which is what Xtend fixes.
I love it.
If you (or GP) are going to argue that C++ is no more productive than C simply because cfront turns C++ into C, then I think theory has gotten in the way of reality.
I have read much detail about Extend, but to me, the key question becomes: does it have language level abstractions that Java does not? I think closures and anonymous functions qualify, but I don't know if they're enough to make that much of a difference.
But what I've seen of Extend, with the exception of closures and anonymous functions, it doesn't actually have any new abstractions. It just cleans up the syntax.
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.
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.
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.
