I’m cur­rently hanging out at my gate in Pear­son air­port. In a couple hours I’ll be on my way to Paris and tomor­row morn­ing I’ll catch my con­nect­ing flight to Ams­ter­dam and then I take the train to Utrecht to see Jasna’s sis­ter, Ana, and her hus­band, Andre.

Jasna and I aren’t very good with sep­ar­a­tion, though I think this time went bet­ter than most. It could be that it’s a shorter sep­ar­a­tion this time — five days, in con­trast to Jasna’s recent two-​​month trip — or that we’re too tired from last night’s Hallowe’en party to get as worked up. Maybe we’re just get­ting bet­ter at it, though. It’s not like no tears were shed, but I think we did rel­at­ively well.

Unfor­tu­nately today my cam­era bat­tery decided to crap out on me. The upside to this is Jasna lent me her (very awe­some) DSLR cam­era for the trip. I’ll try to keep pic­tures of blondes down to a min­imum. Mostly I’m excited to see Ana and Andre, but I think they’ll be busy most of the time, so I’ll prob­ably ven­ture into Ams­ter­dam at least once to enter­tain myself. I brought the cam­era cable with me, so watch my photo gal­lery in the next day or two for pic­tures to start appearing.

The con­fer­ence — and my present­a­tion there — I haven’t thought a whole lot about yet. I’ll have to dis­ap­pear to Eind­hoven, which I think is only about half an hour from Utrecht — but then again maybe everything’s half an hour away from everything in the Neth­er­lands, who knows — and see what’s going on there. I’m fairly excited to see what FOPARA ends up being like since this is the first year the workshop’s being done. I’m espe­cially excited to see the Hume pro­ject people, like Kevin Ham­mond, since I’ve never met any.

I should say there’s still a lot of work that’s going on behind the scenes, work even on what I’m going to present to FOPARA. While I was in Cal­gary we decided to put in a new typ­ing sys­tem based on bunched logics which deals eleg­antly with a lot of the prob­lems with peeks that we’ve been sort­ing out in Pola, plus some new features.

I'm currently hanging out at my gate in Pearson airport. In a couple hours I'll be on my way to Paris and tomorrow morning I'll catch my connecting flight to Amsterdam and then I take the train to Utrecht to see Jasna's sister, Ana, and her husband, Andre. Jasna and I aren't very good with ...

My visit this week to Cal­gary to work with Brian and Robin is com­ing to an end and has def­in­itely paid off again. We have another day at least of work ahead of us, but prob­ably not much more real work will get done by then since we still have the FOPARA paper to fin­ish up and get cam­era ready. But, just in the past couple of days we’ve already made tre­mend­ous pro­gress in improv­ing and sta­bil­iz­ing the lan­guage. It won’t be too much longer before “core Pola” is finalized.

I should say there was one inter­est­ing res­ult that Brian told me about. The peek con­struct is a unique con­struct to the lan­guage, which allows one to, under some restric­tions, break affine­ness, i.e., allows one to ref­er­ence a vari­able mul­tiple times to give the pro­gram­mer more express­ive­ness. It’s a del­ic­ate busi­ness since affine­ness is what keeps Pola pro­grams polynomial-​​time, par­tic­u­larly in the con­text of recur­sion. As it turns out, if you remove the recursion-​​symbol restric­tions on peeks — allow­ing recur­sion within the con­di­tion of a peek—but keep the other restric­tions on peeks, you exactly cap­ture PSPACE! We demon­strated this by chan­ging just a couple lines of code, allow­ing recur­sion, and cod­ing up QSAT to play with. (more…)

My visit this week to Calgary to work with Brian and Robin is coming to an end and has definitely paid off again. We have another day at least of work ahead of us, but probably not much more real work will get done by then since we still have the FOPARA paper to ...

My under­gradu­ate super­visor (from the Uni­ver­sity of Cal­gary), Robin Cock­ett, was in town today on a short visit. My two cur­rent super­visors, Robin and I spent the entire day in a friendly research meet­ing. I sup­pose the biggest bene­fit was the every­one got to meet each other, but we also covered a lot of ground on Pola and what we should be focus­ing on.

The first big change is that we’re going to, again, redo peeks and cases. Peeks and cases have long been a prob­lem with Pola and one which is, so far as I know, com­pletely unique to Pola. In a typ­ical func­tional lan­guage, case con­structs are no mat­ter at all: you have some datum and you case on it to see what it is (is it an empty list or a non-​​empty list?) and go on your way. In Pola things are not so neat and tidy: cent­ral to the work­ings of Pola is the idea that often you’re not allowed to ref­er­ence a vari­able more than once (lest you break out of poly­no­mial time). This restric­tion can be waived, very del­ic­ately, if you prom­ise to only “peek” at a value but not use it. The dis­tinc­tion between a case (“con­sum­ing” a value) and a peek has always been a bit awk­ward, but also very dan­ger­ous to play with if you don’t want to acci­dent­ally allow non-​​polynomial things slip­ping in. I think we’ve finally figured out a good scheme.

The second big change is dis­cuss­ing how to the bounds infer­ence. This is a huge one because hav­ing the com­piler infer bounds is, in my mind, the raison d’être for Pola. I’m almost done imple­ment­ing very loose, clumsy bounds. They’re cor­rect as upper bounds, but they’re so loose as to be nigh use­less. There will never be a per­fect solu­tion to get­ting totally tight bounds and I’m becom­ing increas­ingly aware that there is a huge trade-​​off between being able to get tight bounds on things and hav­ing to carry around a lot of typ­ing inform­a­tion that allows you to infer those bounds. This is what I’ll be spend­ing most of my time on in the near future.

As for the prob­lem I men­tioned last time about hav­ing to imple­ment my own poly­no­mial arith­metic: I just rewrote it myself and I’m happy with it. It works and it’s much cleaner than before.

My undergraduate supervisor (from the University of Calgary), Robin Cockett, was in town today on a short visit. My two current supervisors, Robin and I spent the entire day in a friendly research meeting. I suppose the biggest benefit was the everyone got to meet each other, but we also covered a lot of ...