Lisp Hackers: Christophe Rhodes

Next in our series of interviews with inspiring lispers is a conversation with SBCL's principal maintainer Christophe Rhodes. He was among the first two people to join the project, after it was solely developed for more than a year by William Newman. And he is, probably, the most "stable" contributor, still remaining very active in the community, after more than a decade. What fascinates me personally about him, is the aura of a profoundly creative mind, fiddling with reality in interesting and unexpected ways.

Tell us something interesting about yourself.

I'm a singer, specializing in performance (admittedly somewhat rare at the moment) of unaccompanied music of the European Renaissance. My next concert is Brumel's "Earthquake Mass" with the vocal ensemble De Profundis. I did my doctoral research a few doors down from Stephen Hawking. AndI was a cast member on "Una Stravaganza dei Medici", a reconstruction of the Florentine festivities for the marriage of Ferdinand de Medici and Christine of Lorraine - which means that there's at least some chance I have an Erdős-Bacon number.

What's your job? Tell us about your company.

Oh, well, that's a bit complicated! :-) Most of my time at the moment is spent with Teclo Networks, a Lisp-flavoured startup which is bringing reliability and usability to mobile broadband. I'm on leave of absence to pursue this from Goldsmiths, University of London, where I am a lecturer in Computing, responsible for undergraduate teaching, postgraduate supervision and independent research.

Do you use Lisp at work? If yes, how you've made it happen? If not, why?

I do. I should say that I'm no longer, if I ever was, a programmer by trade; most of my work at Teclo is not writing code, but when I do it is in C, R or Common Lisp. Working in a Lisp-flavoured startup (I'm not the most famous Lisp programmer in the company, and quite some way from being the best...) has made Lisp a natural tool to use when it's appropriate; while it might be a bit of a shame that Lisp is not used exclusively, the balance of idealism and pragmatism is pretty good, and it's fairly satisfying to know that the high-performance network element that we ship has Lisp code controlling its operation.

I wouldn't make an argument that C is a Lisp by any stretch, but I've popped up at a couple of events in the last year to argue that R has some claims to being a Lisp; it has conditions, handlers, restarts, generic functions, macros operating on parse trees... and a SWANK backend.

Another part of what I do is write documents, both for Teclo and for Goldsmiths. I have in the last couple of years fallen in love with org-mode and in particular with "reproducible research", or living documents; the ability to have executable sections of code for generating results, which can then themselves be further analysed by other bits of code — in other languages, if that's appropriate — and the whole exported as a document typeset to what I consider to be high-quality standards. The fact that there is also acceptable-quality web output from the exact same process is gravy.

What brought you to Lisp? What holds you?

Two seminal moments on my road to Lisp: the first was, as an undergraduate, getting a job in the summer of 1997 to work on simulating fluid dynamics in the context of galaxy formation, to assist in trying to understand how the spiral arm structures form. I'd being told "here is K&R, here is USENET, here is XEmacs, here is Tcl; in five weeks let's see what you've come up with" — I distinctly remember reading comp.lang.lisp and a "Lisp is slow" thread, with active participants combating the troll with disassembly.

The second, a few years later, was wandering into the #lisp IRC channel on openprojects, to find an almost-empty channel, about 10-20 participants; one of whom was there twice (dan_b and dan`b), using the channel to paste bits of alpha assembly between his laptop and his desktop, in his efforts to get SBCL on alpha working.

As for what keeps me, well, when what I have to do is solve problems that no language has built-in libraries for (scalable audio similarity detection, say, or musical structure inference) then I want to be working in a language where I can focus on the problem itself, rather than the detail of that language — and for me, Lisp permits that kind of separation of concerns, given its easy support for DSL and embedded language generation, protocols, and the ability to run partial programs.

Among software projects you've participated in what's your favorite?

I enjoyed most working on an editor for lute tablature, I think. Partly because it was a chance to learn about things (parsing, CLIM, user interfaces) that I hadn't really thought about before. Partly because of the feeling of being able to build up incrementally and rapidly from a very simple prototype to deliver something which was actually useful; and partly because it was also interesting to learn about the problem domain. Gsharp (G#), the score editor largely designed by Robert Strandh, is an editor for what you might call "common practice" notation: five lines in a staff; dots and lines to indicate pitch (by height) and duration (by glyph) of notes. In my research group at Goldsmiths, though, we have a lutenist (a player of the lute) who had a research project on cataloguing and transcribing a particular repertoire of 16th-century lute music, which was notated in "tablature": six lines, one per string of the lute; letter or number glyphs on each line to indicate finger position; and glyphs above the staff to indicate duration.

The point about this was that when I first came on the scene the project had a truly awful workflow, because they had a batch renderer from the textual format to encode this music to something visual. This made the process of encoding painful, in particular for the error correction phase: it was fairly easy to find an error in the visual rendering, but to go from there to the text corresponding to it was painful. So I wrote a little CLIM app with an editor buffer and a display; the display was a rendering of the "Tabcode" in the editor buffer, and each glyph in it was associated with a text cursor position, so that you could click on the display and have the editor cursor warp to the Tabcode corresponding to the glyph. This was a productivity win for the project.

What's the most exciting use of Lisp you had?

I don't get easily excited by technology. So for me, what was exciting was seeing a community of users and developers grow around SBCL — in particular, working with extremely focused and motivated individuals on improving the system, subject to all sorts of constraints, not least those imposed by real-world uses (including the QPX poster-child of ITA Software).

SBCL contributors seem to be a very active, closely-knit, and united community. How did that happen? Maybe you could share some insight into the history of the project. Also what were the factors, that determined its success?

I think part of SBCL's success as a community was the finding of like minds — which came about partly because it started off as a project when access to information channels was growing, but also partly because there were some explicit principles laid down: Bill Newman made it very clear that he was aiming for something maintainable, and also taught by example the meaning of maintainability. In the SBCL source distribution, there are over 100 lines of textual detail describing his ideas about what he was aiming for, and although it's nothing like an explicit charter which every SBCL developer (or user!) has to sign up to, it's nevertheless a useful indication of a direction to drive in. Both detailed and motivated enough that even a graduate student with no software development experience could understand that there were tradeoffs involved, and someone had thought hard about which side of the tradeoffs they wanted to be. I'd also point out some of Bill's advodiary entries of the time, including http://www.advogato.org/person/wnewman/diary/6.html and http://www.advogato.org/person/wnewman/diary/9.html, which perhaps illustrate that he was thinking about this kind of software maintenance all the time. ("To foil the maintenance programmer..." :-)

I think this is particularly important when the bulk of the work is done by volunteers; it helps to keep focus (I've written before about how software is only sustainable if it can stay alive in the minds of its developers).

If you had all the time in the world for a Lisp project, what would it be?

There's lots that I'd like to do, both hacking on Lisp itself and things I'd like to explore, for which I'm likely to reach for Lisp first. I'd also like to get more fluent with emacs lisp, enough to be able to quickly write the user interfaces I would like to use to various bits of software that I use every day.

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