Visit month: Princeton

by Edward Z. Yang

If you haven't noticed, these are coming in the order of the visit days.

Whereas the weather at UPenn was nice and sunny, the NJ Transit dinghy rolled into a very misty Princeton. Fortunately, I had properly registered for this visit day, so the hotel was in order. I was a bit early, so I met up with an old friend who had recently penned this short story and we talked about various bits and bobs ("I hear you're up for a Hugo!") before I meandered over to the computer science building.

The Princeton campus also holds some distinctive memories for me, a patchwork of experiences of my high school self, including a unpleasant month temping for the Princeton Wind Ensemble (I've been since informed that the ensemble is much healthier now), visits to the area for various reasons, a fascinating interview in which I was told that "I should not go to Princeton", and a very pleasant, if slightly out-of-place, campus preview weekend. Of course, it is the case that graduate student life is completely different from undergraduate life, so I was prepared to shelve these experiences for my second visit.

One of the most interesting things I realized about Princeton computer science, during Andrew Appel's speech during the admit's reception dinner, was how many famous computer scientists had graded Princeton with their presence at some point or another; these included Church, Turing, Gödel, Neumann, and others... One of the insights of his talk was this: “maybe your PhD thesis doesn’t need to be your most important work, but maybe you can have a four page aside which sets forth one of the most important techniques in computer science.” (He was referring to Alan Turing’s thesis, in which he introduced the concept of relative computing.)

Some "facts": at Princeton, your advisors work to get you out, so you don't have to worry about dallying too long on the PhD. Being a part-time student is not ok, and Princeton does have qualifying exams, but you'll probably pass. (The overall wisdom that I came away with here is that computer science quals are very different from quals in other PhD disciplines, where the qual is very much a weeder. In CS, they want you to pass.) The generals are in some sense a checkpoint, where you can figure out whether or not you're happy with the research you're doing with your advisor. You need to take six classes, four in distribution, but you can pass out of the final. You spend your second year teaching, both semesters as a "preceptor". You pick your advisor at the end of your first year, and five people serve on your thesis committee (it tends not to be too adversarial). You're relatively shielded from grants.

Andrew Appel is a very smart man. He’s been recently working with my current advisor Adam Chlipala, and their research interests have some overlap. He is working on a verified software toolchain, but he's also happy to tackle smaller problems. One of the small theoretical problems he showed us during our three-on-one meeting was the problem of calculating fixpoints of functions which are not monotonic, but instead oscillate towards some convergence (this occurs when the recursion shows up in the contravariant position; as strange as this may seem, this shows up a bit in object oriented languages!) One of his grad students told me he likes "semantic definitions", and is not afraid to take on large challenges or tackle the gritty details of languages like Cminor, integer alignment, or scaling up theoretical techniques for large programs. And despite being department chair, it's easy to schedule time with him, and he seems to have this uncanny ability to generate grants.

David Walker is very excited about the Frenetic programming language, which is a language for dealing with network programming. I already had a bit of context about this, because Jennifer Rexford had given an invited talk at POPL about this topic. One of the interesting things I noticed when hearing about OpenFlow for the second time was how similar its handling of unknown events was to hardware: if the efficient lookup table doesn't know what to do, you interrupt and go to a slow, general purpose computer, which figures out what to do, installs the rule in the lookup table, and sends the packet on its way. The three of us might have been a technical mood, because we ended up asking him to give us the gory details of per-packet consistency when updating network rules. I hear in another life David Walker also did type systems, and has also done a bit of work in semantics. One contrast a grad student noted between Appel and Walker was that Appel would assume you know what he is talking about (so it's your onus to interrupt him if you don't: a useful skill!), whereas Walker will always go and explain everything and always stop you if he doesn't know what you're talking about. This makes him really good at communicating. (Oh, did I mention Frenetic is written in Haskell?)

Randomly, I discovered one of the current grad students was the creator of He does PL research now: but it's kind of nifty to see how interests change over the years...