Lambda the Ultimate

I would like to call the attention of LtU readers to some ongoing language design efforts in the XQuery standards community. Regardless of my ridiculous opinions about current proposals (some of which I've shared below) I think we can all see that this community-based language design effort is likely to have huge impact: many important systems will be built using the language design that emerges. So, the zero-order point of this post is just to offer some hopefully orienting links, and then I'll opine a little bit, hoping to add something new:

It all starts with the XQuery 1.0 standard. If you are utterly new to it, like I was not long ago, there is a product manual that rewards a quick skim with the gist of what XQuery is about. It is an Introduction to Berkeley DB XML (an open source product).

XQuery is a pure, functional language taking XML types (hereafter "XDM" for XML Data model) as its value typing system. It (mostly) lacks higher-order functions. It is an expression language with expressions taking and returning named tuples or anonymous lists of values. Tail call optimization is provided. Closures and continuations are not. That is where recent developments start.

Three proposals have come to my attention. All are very nice in their ways (though, I opine below, each is a mistake). These proposals are:

1. XQuery Update Facility which introduces a monadic style of I/O to XQuery, mainly by adding new value types which functions may return (the type of "pending update" values).

2. XQueryp which introduces sequencing operators (operators to control execution order in this formerly pure language).

2. (D. Chamberlain, K. Beyer, L. Colby, F. Ozcan, H. Pirahesh, and Y. Xu) Extending XQuery for Analytics. Proceedings of the 2005 ACM SIGMOD Conference, Baltimore, June 2005. which adds an interesting ad hoc kind of list comprehension to XQuery, inspired by SQL's "GROUP BY" and related constructs.

So, free of my opinions: it seems that there's a fairly serious effort afoot to turn XQuery into a general purpose systems programming language for web applications. I sense from the literature that the crossover of db-expert and language design experts hasn't been all that strong, in this area. I hope that among the audience of LtU, some language design experts might help change that.

So, my opinions, which are naturally unjustifiably critical and self-promoting:

I think that the proposed sequencing constructs and update facility are superfluous. Without any changes at all to XQuery 1.0 I was able to add monadic I/O along with a generalization of closures and continuations in XQVM. My solution is a non-intuitive way to achieve the same aims but I'm finding that it works out very nicely.

The addition of a "group by" construct to XQuery seems a mistake to me. It is just syntax -- it can be trivially translated into strict XQuery 1.0 in a way that implementations should have little difficulty optimizing. The literature around the issue has just been overlooking that transformation. (They are just about all assuming that the transformation should use the "fn:distinct-values" operator and the optimizer will have to cope with that. If they tried solving the same problems without using that operator, they'd probably discover the transform I have in mind.)

My opinions aside: what should really happen to XQuery? What are other takes on these new developments?