Finally! It's over! Never again! The defense mostly followed the specified procedure. I first had about 45 minutes to give a presentation of the results of the dissertation, then the first opponent, Neil Jones, gave a 15 minute summary putting my work into a larger context.

After his summary, he proceeded to ask several high-level questions about various parts of the dissertation. One question I liked a lot was (paraphrased): "are the axiom-based Java testing techniques you propose in your case study applicable to Stratego and would you actually use them?". All the tools and prototypes discussed in the thesis are written in Stratego, and are applied to Java, C and a toy language called TIL. However, few of the tools are actually available for Stratego itself. This is the classical story of the cobbler's children's shoes... I certainly think it would be worthwhile to do the work necessary to make some of the the tools available to Stratego as well.

Peter Mosses followed with a series of detailed questions. Clearly, Peter had read the text and figures very carefully, because some of his questions were about rather subtle issues and ambiguities in my work. There were also a few (fortunately minor) mistakes that made some of the figures more difficult to comprehend than necessary. He also nailed me on a very embarrassing definite-instead-of-indefinite article mistake. Normally, these things do not matter very much, but in this particular sentence it sort of reversed one of my main arguments in the dissertation. Whoops;)

After I'd answered their questions as best as I could, they retired to discuss whether my performance was good enough. This is mostly a formality in the current tradition, so I can't say I was very worried at that point. Once they came back, the dean proclaimed my successful completion of the degree, and we all rushed off for some (sadly delayed) champagne and cake.

I even wore a suit, and here's a picture to prove it:

Much thanks to Uwe Wolter, who was the local member of the committe and therefore the grand orchestrator of all the formalities, the formal parts went smoothly. After the defense, the stressful part of the day started: I had to collect all people's menu choices for the evening, send my family and friends shopping for the evening's party, clean the apartment and of course smear huge swaths of marzipan cake all over my suit. Thanks to very good help from my brother, his girlfriend, Håvard (my roommate) and my mother, and Tilde, we managed to get ready just in time to arrive ten minutes late for the scheduled dinner.

Magne and Peter:

Neil and Uwe:

Tilde:

Since Eelco took the pictures, he's not in any of them. Fortunately, Tilde has a few pictures of Eelco, and of the other people present. I'm still waiting for those and will upload a few once I get them (and get some green lights from the people depicted).

After dinner, we all (committee, advisors, friends and family) drove back to my apartment and Tilde whipped up drinks to all. She even tricked one into me;) I was very pleased to see that my office neighbour and student advisor, Ida Holen, found the time to show up. Also, I had friends flying in from Oslo (okay, Holmestrand) and Trondheim for the event, namely Karl Thomas, Karina and Leif Olav. Thanks guys! Hope the drinks and food was worth it;) The usual Bergen posse showed up as well, including Stig, Fay, Knute, Glenn, Espen, Tommy x 2 and Paul Simon (if I forgot somebody, ping me).

Disputasen min blir onsdag 27. juni kl 13:00 [mulig dette blir flyttet pittelitt avhengig av flyforsinkelser] i rom 2144 (Store Auditorium), Datablokken, Høyteknologisenteret i Bergen. Alle som er interessert er hjertelig velkomne til å dukke opp. Ring eller send e-post hvis du vil ha retningsanvisning

Komiteen er Neil D. Jones, Peter D. Mosses og Uwe E. Wolter.

Jeg får først ca 40 minutter til å presentere oppgaven, deretter skal Neil Jones gi et 15 minutters sammendrag. Etter dette kommer det egentlige forsvaret, der komiteen og tilskuere stiller spørsmål. Etterhvert blir enten hele greia forkastet eller så går tilskuermengden tom for spørsmål. I begge tilfeller avsluttes seansen.

I samsvar med innleveringsritualet har komiteen har allerede evaluert (og anbefalt forsvar av) den innleverte oppgaven. Papirkopier finnes i universitetsbiblioteket, på mat.nat.-filiane. En reformattert (etter universitetets profilmal, må vite), korrigert versjon vil bli gjort tilgjengelig i trykket form på disputasen.

På kvelden, rundt 21:00-tiden (også onsdag 27. juni) blir det fest. Sted er ikke avklart enda, men jeg annonserer det så fort jeg finner ut. Igjen, alle som er tørste, sultne eller selskapslystne er naturligvis velkomne.

Eelco and I have a second paper at the LDTA workshop this year -- a tool description paper about Spoofax. The paper is very space-constrained, so we dropped the abstract, but if we had one, it would read like this:

Many programmable software transformation systems are based around novel domain-specific languages, with a long history of development and successful deployment. Despite their reasonable maturity and applicability, these systems are often discarded as esoteric research prototypes partly because the languages are frequently based on less familiar programming paradigms such as term and graph rewriting or logic programming, and partly because modern development environments are rarely found for these systems. The basic and expected interactive development aids such as source code navigation, searching, content completion, real-time syntax highlighting and error checking, are rarely available to developers of transformation code.

In this system description paper, we introduce Spoofax, an interactive development environment based on Eclipse for developing program analyses and transformations with Stratego/XT -- a language and toolset for developing stand-alone software transformation systems based on formal language descriptions. Spoofax provides the aids mentioned above, in addition to a code outliner and incremental building of projects, and thus significantly eases the development of language processing tools using Stratego/XT. Furthermore, Spoofax is extensible with scripts written in Stratego that are executed within Eclipse, and allow live analyses and transformations of the code under development.

(pdf, bib)

There is already a website for Spoofax, www.spoofax.org, but it's hardly inviting and informative. I have a new one in SVN, but as always, I tend to spend my time hacking code instead of making releases and web pages. I'll try to remedy that very soon.

Together with Eelco Visser, I got a paper (two actually, see the other post) accepted to this year's Workshop on Language Descriptions, Tools and Applications, which is held in Braga Portugal. My visit to IBM Research last summer started me thinking about a good way to integrate existing compiler frontends with Stratego/XT. This is the result, and I think it turned out quite well.

Transformation systems such as Stratego/XT provide powerful analysis and transformation frameworks and concise languages for language processing, but instantiating them for every subject language is an arduous task, most often resulting in half-completed frontends. Open compilers, like the Eclipse Compiler for Java, provide mature frontends with robust parsers and type checkers, but solving language processing problems in general purpose languages without transformation libraries is tedious. Reusing these frontends with existing transformation systems is therefore attractive. However, for this reuse to be optimal, the functional logic found in the frontend should be exposed to the transformation system -- simple data serialization of the abstract syntax tree is not enough, as this fails to expose important compiler functionality, such as import graphs, symbol tables and the type checker.

In this paper, we introduce a scriptable analysis and transformation framework for Java built on top of the Eclipse Java compiler. The framework consists of an adapter extracted from the abstract syntax tree of the compiler, and an interpreter for the Stratego language. The adapter allows the Stratego interpreter to rewrite directly on the compiler AST. We illustrate the applicability of our system with scripts written in Stratego that perform framework and library-specific analyses and transformations.

(pdf, bib)

The prototype code is already available in the Spoofax SVN repo, but I will clean it up and make a separate release once I get a bit of breathing space from my thesis writing.

Anya, Valentin, Magne and myself recently wrote a paper that was presented at GPCE this year. Valentin and me implemented the extension using the Transformers transformation system (Valentin did most of the hacking for C -- I was hacking for TIL. More on that later). We designed the extension to capture most of Magne's original idea into the result. Anya helped out with the writing and finding illustrative examples.

Abstract

Dealing with failure and exceptional situations is an important but tricky part of programming, especially when reusing existing components. Traditionally, it has been up to the designer of a library to decide whether to use a language's exception mechanism, return values, or other ways to indicate exceptional circumstances. The library user has been bound by this choice, even though it may be inconvenient for a particular use. Furthermore, normal program code is often cluttered with code dealing with exceptional circumstances.

This paper introduces an alert concept which gives a uniform interface to all failure mechanisms. It separates the handling of an exceptional situation from reporting it, and allows for retro-fitting this for existing libraries. For instance, we may easily declare the error codes of the POSIX C library for file handling, and then use the library functions as if C had been extended with an exception mechanism for these functions -- a moulding of failure handling to the user's needs, independently of the library designer's choices.

(pdf, bib)

The code for this experiment will be released shortly, once Anya finishes the final set of examples that we will bundle with the release. She's been a bit under the weather lately, but hopefully she'll shake it off pretty soon. I will post about the release when it happens.

Barry Pekilis, a very good friend of mine with whom I spent countless evenings and weekends while in Waterloo, passed his PhD defense yesterday.

I think this is quite an outstanding achievement on Barry's part. I know how Real Life has intervened almost at every turn for Barry, trying to its best to sabotage his project. The fact that dr. Pekilis has finally succeeded is a testament to the good doctor's incredible tenaciousness.

It's also in order to congratulate Krzysztof Czarnecki with successfully kicking another student out of the coop:)

Eelco Visser and myself have a paper at the sixth international Workshop on Reduction Strategies in Rewriting and Programming (WRS'06), coming up next week.

Abstract

Some transformations and many analyses on programs are either difficult or unnatural to express using terms. In particular, analyses that involve type contexts, call- or control flow graphs are not easily captured in term rewriting systems. In this paper, we describe an extension to the System S term rewriting system that adds references. We show how references are used for graph rewriting, how we can express more transformations with graph-like structures using only local matching, and how references give a representation that is more natural for structures that are inherently graph-like. Furthermore, we discuss trade-offs of this extension, such as changed traversal termination and unexpected impact of reference rebinding.

bib - pdf

The final version of the article Stratego: A Programming Language for Program Manipulation is now online on the ACM Crossroads site. It is a very lightweight introduction to program transformation, why we do it, and how it works.

Abstract

Programming languages have a dual role in the construction of software. The language is both our substrate (the stuff we make software from), and our tool (what we use to construct software). Program transformation (PT) deals with the analysis, manipulation and generation of software. Therefore a close relationship exists between program transformation and programming languages, to the point where the PT field has produced many domain-specific languages for manipulating programs. In this article, I will show you some interesting aspects from one of these languages : Stratego.