gzochi

After releasing libRUIN a couple of months ago, I had some bandwidth to take on some new stuff, and I decided to revisit the project that had initially gotten me interested in user interface markup and GNU Guile in the first place: gzochi, my Free MMO game platform, ambitiously named after Xochipilli, the Aztec god of games and gambling.

My initial work on gzochi, while it took me down some interesting and fruitful paths (i.e., practically every Free Software project I've been working on for the past eight years), was probably all wrong. The system I'd envisioned involved a direct, first-class server-side model of the UI state of all connected clients, with practically nothing between that and the networking layer. I still want to use gzochi to explore things like dynamic UI deployment, but in the intervening years I've also learned that there's a layer for everything, and I wannt to keep the scope of each layer manageable.

So this time around I decided to decompose the problem a bit more aggressively, and I'm taking my architectural cues from a software project I'd worked with in a professional capacity, the Sun Game Server, aka Project Darkstar, aka RedDwarf Server, which takes the approach I had in mind insofar as providing a server container for games, but which makes no assumptions about the details of the games it hosts beyond providing some general "services" to them. To wit: There are message delivery services, a data retrieval service, and a task scheduling service; and "userland" game code is executed transactionally with respect to these services in order to hide the nasty details of concurrency.

The implementation of gzochi I'm currently pursuing steals the best parts of this architecture while replacing the server container bits with C code (with help from GNU Serveez) and replacing the game bits with Guile Scheme. I've got a working prototype of most of the system. Think this sounds interesting? Come aboard!

libRUIN

...version 0.2.0 is out! Holy cow, it's been four and a half years. There are a ton of improvements (do see the NEWS file if you're interested), but just as significantly, this release was made possible by improvements in and releases of a bunch of libRUIN's dependencies -- specifically GNU Guile and the SCSS and SDOM Scheme libraries.

And there were improvements (I hope) to my thinking about software development. If I can wax enlightened for a moment, here are a few observations / edicts that occurred to me as I was working on this release:

Avoid friction in code by getting the data model right.

I've found while working on libRUIN and other projects that code that's difficult to extend or refactor is often the result of an incomplete or incorrect data model. When I sketched out the initial architecture for the library, I think I was trying to keep the number of data structures it depended on low, both in the user-facing API and the internals. If data structure A has the same general shape as data structure B, I thought, why not just wedge A into this B-shaped hole? In retrospect, the additional size and complexity created by adding a few new struct typedefs was trivial compared to the disadvantages in legibility and flexibility brough about by inappropriate re-use of data structures. So: If your model needs a rich set of data structures to be accurate, so be it!

When a specification suggests a model, try that one first.

I spent a long time trying to figure out which parts of the CSS recommendation I could ignore by virtue of my only needing to render markup to a terminal. In doing so, though, I failed to pick up on the fact that a lot of the conceptual framework suggested by the recommendation is actually prescribed by it as well. For example, the "box model" isn't just a useful way of thinking about layout and rendering; it's really quite difficult to implement certain features of the recommendation without actually creating a first class representation of boxes. In retrospect this seems obvious, but at the time I was sure there was no way all of the formal complexity I saw in the spec could possibly be required for the work I was doing. The deeper I got, though, the clearer it became that the recommendation was the result of a long and fruitful two-way collaboration between the standards body and a number of successful "reference" implementations, and that ignoring the models derived from this relationship was actually making my life more difficult: Implementing support for things like the "white-space" property would be practically impossible unless I'd also baked the concepts of line boxes and inline content splits into my code. And I suspect a lot of successful specifications have in common the property that they are both describing requirements as well as the shortest path to meeting them. So: Until you've got a reason to do otherwise, let the specification guide your thinking.

Unit tests are worth it.

The original "test suite" for libRUIN was a set of XHTML documents and accompanying stylesheets from the W3C's CSS2.1 site. When I wanted to verify that a new feature was working or that I hadn't broken anything, I would feed these documents into a sample application and visually inspect the output to make sure it looked right. Obviously, moving to a suite of automated tests for each phase of the rendering pipeline made assessing the quality of the code much quicker. But I think the real benefit of unit tests is more subtle. By applying compile- and execution-time constraints to code, you control the way in which it can change. And by requiring that your code have entry points for unit tests to call, they enforce a layered, more modular architecture. Unit tests apply pressure on code that keeps it in good shape.

(This is probably all covered by a bunch of books and web sites about testing that I haven't read.)

That's all I've got. Take a look at libRUIN, and jump in if you can -- there's a ton more shit to do.

SCSS

I've just release SCSS 0.4.2, a bugfix release that builds upon the stability of 0.4.1. The bugfixes and API changes added here are a direct result of my making a lot of really exciting progress recently on a new, long-overdue release of libRUIN: The list of "I'm going to have to address that at some point"-type details -- for both SCSS and libRUIN -- is getting shorter and shorter.

Tarball is here. See also NEWS.

r6rs-protobuf

...version 0.2 is out! Downloads are here. I've added support for default values for optional fields and fixed some issues (mostly around enumerated types) that I discovered along the way.

One thing I noticed while writing SRFI-64 unit tests, though, was how neatly the `environment' procedure in the R6RS `(rnrs eval)' library works for testing code generation. My code generation routines return lists of datums representing expressions for creating the required bindings for a particular data type definition. `environment' allows for the creation of ad hoc "sandboxes" in which these binding expressions can be evaluated -- and in which test expressions can also be evaluated so that you can make assertions about the behavior of the stuff you bound. To wit:


(define test-env (environment '(rnrs)))
(for-each (lambda (expr) (eval expr test-env))
(protoc:generate-message my-message-def))
(test-assert (protobuf:message-builder? (eval '(make-my-message-builder) test-env)))


And you can create a new sandbox for every test, so that you don't have to worry about bindings generated by previous test cases polluting the environment of subsequent test cases that generate code for the same input definitions.

r6rs-protobuf

...version 0.1 is out! Check out the project page or go straight to the downloads. The thing's almost feature complete (haven't tackled "services" yet), but I decided to keep the version number low because the test suite is a bit anemic, and, of course, to account for bugs.

That was fun!