Monday, July 13, 2009

ECOOP day 1 - FTfJP and SToP

And so to the conference; first day - the FTfJP and SToP workshops. The former good, the latter great, it really seemed a workshop in the right place at the right time.

I spent the morning at FTfJP, including presenting my paper on wildcards and subtyping, which was surprisingly well received. It seemed to get people thinking and I got good questions. I was very worried that it would be a hard sell and people wouldn't see the point, but thankfully I was proved wrong.

The invited talk was by Todd Millstein and was on his generic effects system. Unfortunately I was rather tired and couldn't pay much attention, but it was a good talk on an interesting topic. I highly recommend the paper which (I think) was at TLDI this year. The most interesting thing I took away from the talk was the relationship between effects and permissions, which is something I've been thinking about myself rather a lot recently.

The first technical talk was A Typed Intermediate Language for Supporting Interfaces by Juan Chen. What I found interesting was the use of existential types for class types which I've also made use of. It is interesting here because she is using them for, essentially, implementation reasons in the intermediate language; specifically to give types to iTables for dispatching method calls on interface types.

Next up was Range Parameterized Types: Use-site Variance without the Existential Questions by Bruno De Fraine which proposes a simpler version of Java wildcards. The system is less complex, but this should not be surprising as it is less complex. In particular there seems no difference from existential types which cannot be unpacked over a scope (i.e., wildcards capture). Although the formalism is direct, it is significantly more complicated (and less elegant) than an existential types system.

Reuben Rowe then presented Semantic Predicate Types for Class-based Object Oriented Programming. This proposed adapting and generalising intersection types to the OO world as predicates and presented an approximation theorem which, I'm afraid, went slightly over my head. I will be reading the paper though...

After lunch I switched workshop and Attended SToP which was a proper workshop (as opposed to a mini-conference) and had a lot of discussion; it was, therefore, running an hour behind schedule. Which meant that I could catch the second half of Phil Wadler's talk. This reminded me how good a speaker he was and also how cool the blame thing is. On the downside, the talk was very similar to the one I saw at ESOP a few months ago. It included the same division of subtyping into four variations and higher order casts, but added polymorphism. This turns out to be surprisingly difficult - it interacts badly with some of the subtyping.

Next was a talk on Diamondback Ruby which I remember being interesting, but my notes of the talk are terrible.

The next talk (I'm on the plane now and so can't look up the titles/authors, sorry) was about typing in scheme and had the interesting conclusion that type checking extended with gradual typing improved expressivity, even when no dynamic typing was used!

Next up: Atsushi Igarashi's student with progress towards gradual typing in FGJ. Mathias didn't seem to think that this was gradual typing at all. They used a type dynamic, denoted with a question mark, but which didn't correspond (with generics) to wildcards. This seemed unnecessarily confusing.

The final talk (presented by Gregor and his crazy hat) analysed Javascript programs in order to find out how many (and which) dynamic features were used. The conclusion seemed to be quite a lot in real life, but in quite fixed patterns. Also that Sunspider is not a realistic set of benchmarks.

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