Wednesday, April 20, 2022

In memoriam: Eelco Visser (1966-2022)

On Tuesday 5 April 2022 I received the unfortunate news that my former master's and PhD thesis supervisor: Eelco Visser has unexpectedly passed away.

Although I made my transition from academia to industry almost 10 years ago and I have not been actively doing academic research anymore (I published my last paper in 2014, almost two years after completing my PhD), I have always remained (somewhat) connected to the research world and the work carried out by my former supervisor, who started his own programming languages research group in 2013.

He was very instrumental in the domain-specific programming languages research domain, but also in the software deployment research domain, a very essential part in almost any software development process.

Without him and his ideas, his former PhD student: Eelco Dolstra would probably never have started the work that resulted in the Nix package manager. As a consequence, my research on software deployment (resulting in Disnix and many other Nix-related tools and articles) and this blog would also not exist.

In this blog post, I will share some memories of my time working with Eelco Visser.

How it all started

The first time I met Eelco was in 2007 when I was still a MSc student. I just completed the first year of the TU Delft master's programme and I was looking for an assignment for my master's thesis.

Earlier that year, I was introduced to a concept called model-driven development (also ambiguously called model-driven engineering/architecture, the right terminology is open to interpretation) in a guest lecture by Jos Warmer in the software architecture course.

Modeling software systems and automatically generating code (as much as possible), was one of the aspects that really fascinated me. Back then, I was already convinced that working from a higher abstraction level, with more "accessible" building blocks could be quite useful to hide complexity, reduce the chances on errors and make developers more productive.

In my first conversation with Eelco, he asked me why I was looking for a model-driven development assignment and he asked me various questions about my past experience.

I told him about my experiences with Jos Warmer's lecture. Although he seemed to understand my enthusiasm, he also explained me that his work was mostly about creating textual languages, not visual languages such as UML profiles, that are commonly used in MDA development processes.

He also specifically asked me about the compiler construction course (also part of the master's programme), that is required for essential basic knowledge about textual languages.

The compiler construction course (as it was taught in 2007) was considered to be very complex by many students, in particular the practical assignment. As a practical assignment, you had to rewrite the a parser from using GNU Bison (a LARL(1) parser) to LLnextgen (a LL(1) parser) and extend the reference compiler with additional object-oriented programming features. Moreover, the compiler was implemented in C, and relied on advanced concepts, such as function pointers and proper alignment of members in a struct.

I explained Eelco that despite the negative image of the course because of its complexity, I actually liked it very much. Already at a young age I had the idea to develop my own programming language, but I had no idea how to do it, but when I was exposed to all these tools and concepts I finally learned about all the missing bits and pieces.

I was also trying to convince him that I am always motivated to deep dive into technical details. As an example, I explained him that one of my personal projects is creating customized Linux distributions by following the Linux from Scratch book. Manually following all the instructions in the book is time consuming and difficult to repeat. To make deploying a customized Linux distribution doable, I developed my own automated solution.

After elaborating about my (somewhat crazy) personal project, he told me that there is an ongoing research project that I will probably like very much. A former PhD student of his: Eelco Dolstra developed the Nix package manager and this package manager was used as the foundation for an entire Linux distribution: NixOS.

He gave me a printed copy of Eelco Dolstra's thesis and convinced me that I should give NixOS a try.

Research assignment

After reading Eelco Dolstra's PhD thesis and trying out NixOS (that was much more primitive in terms of features compared to today's version), Eelco Visser gave me my first research assignment.

When he joined Delft University of Technology in 2006 (a year before I met him) as an associate professor, he started working on a new project called: WebDSL. Previously, most of his work was focused on the development of various kinds meta-tools for creating domain specific languages, such as:

  • SDF2 is a formalism used to write a lexical and context free syntax. It has many interesting features, such as a module system and scannerless parsing, making it possible to embed a guest language in an host language (that may share the same keywords). SDF2 was originally developed by Eelco Visser for his PhD thesis for the ASF+SDF Meta Environment.
  • ATerm library. A library that implements the annotated terms format to exchange structured data between tools. SDF2 uses it to encode parse/abstract syntax trees.
  • Stratego/XT. A language and toolset for program transformation.

WebDSL was a new step for him, because it is an application language (built with the above tools) rather than a meta language.

With WebDSL, in addition to just building an application language, he also had all kinds of interesting ideas about web application development and how to improve it, such as:

  • Reducing/eliminating boilerplate code. Originally WebDSL was implemented with JBoss and the Seam framework using Java as an implementation language, requiring you to write a lot of boilerplate code, such as getters/setters, deployment descriptors etc.

    WebDSL is declarative in the sense that you could more concisely describe what you want in a rich web application: a data model, and pages that should render content and data.
  • Improving static consistency checking. Java (the implementation language used for the web applications) is statically typed, but not every concern of a web application can be statically checked. For example, for interacting with a database, embedded SQL queries (in strings) are often not checked. In JSF templates, page references are not checked.

    With WebDSL all these concerns are checked before the deployment of an web application.

By the time I joined, he already assembled several PhD and master's students to work on a variety of aspects of WebDSL and the underlying tooling, such as Stratego/XT.

Obviously, in a development process of a WebDSL application, like any application, you will also eventually face a deployment problem -- you need to perform activities to make the application available for use.

For solving deployment problems in our department, Nix was already quite intensively used. For example, we had a Nix-based continuous integration service called the Nix buildfarm (several years later, its implementation was re-branded into Hydra), that built all bleeding edge versions of WebDSL, Stratego/XT and all other relevant packages. The Nix package manager was used by all kinds of people in the department to install bleeding edge versions of these tools.

My research project was to automate the deployment of WebDSL applications using tooling from the Nix project. In my first few months, I have packaged all the infrastructure components that a WebDSL application requires in NixOS (JBoss, MySQL and later Apache Tomcat). I changed WebDSL to use GNU Autotools as build infrastructure (which was a common practice for all Stratego/XT related projects at that time) and made subtle modifications to prevent unnecessary recompilations of WebDSL applications (such as making the root folder dynamically configurable) and wrote an abstraction function to automatically build WAR files.

Thanks to Eelco I ended up in a really friendly and collaborative atmosphere. I came in touch with his fellow PhD and master's students and we frequently had very good discussions and collaborations.

Eelco was also quite helpful in the early stages of my research. For example, whenever I was stuck with a challenge he was always quite helpful in discussing the underlying problem and bringing me in touch with people that could help me.

My master's thesis project

After completing my initial version of the WebDSL deployment tool, that got me familiarised with the basics of Nix and NixOS, I started working on my master's thesis which was a collaboration project between Delft University of Technology and Philips Research.

Thanks to Eelco I came in contact with a former master's thesis student and postdoc of his: Merijn de Jonge who was employed by Philips Research. He was an early contributor to the Nix project and collaborated on the first two research papers about Nix.

While working on my master's thesis I developed the first prototype version of Disnix.

During my master's thesis project, Eelco Dolstra, who was formerly a postdoc at Utrecht University joined our research group in Delft. Eelco Visser made sure that I got all the help from Eelco Dolstra about all technical questions about Nix.

Becoming a PhD student

My master's thesis project was a pilot for a bigger research project. Eelco Visser, Eelco Dolstra and Merijn de Jonge (I was already working quite intensively with them for my master's thesis) were working on a research project proposal. When the proposal got accepted by NWO/Jacquard for funding, Eelco Visser was the first to inform me about the project to ask me what I thought about it.

At that moment, I was quite surprised to even consider doing a PhD. A year before, I attended somebody's else's PhD defence (someone who I really considered smart and talented) and thought that doing such a thing myself was way out of my grasp.

I also felt a bit like an impostor because I had interesting ideas about deployment, but I was still in the process of finishing up/proving some of my points.

Fortunately, thanks to Eelco my attitude completely changed in that year -- during my master's thesis project he convinced me that the work I was doing is relevant. What I also liked is the attitude in our group to actively build tools, have the time and space to explore things, and eat our own dogfood with it to solve relevant practical problems. Moreover, much of the work we did was also publicly available as free and open source software.

As a result, I easily grew accustomed to the research process and the group's atmosphere and it did not take long to make the decision to do a PhD.

My PhD

Although Eelco Visser only co-authored one of my published papers, he was heavily involved in many aspects of my PhD. There are way too many things to talk about, but there are some nice anecdotes that I really find worth sharing.


I still remember the first research conference that I attended: OOPSLA 2008. I had a very quick publication start, with a paper covering an important aspect of master's thesis: the upgrade aspect for distributed systems. I had to present my work at HotSWUp, an event co-located with OOPSLA 2008.

(As a sidenote: because we had to put all our efforts in making the deadline, I had to postpone the completion of my master's thesis a bit, so it started overlap with my PhD).

It was quite an interesting experience, because in addition to the fact that it was my first conference, it was also my first time to travel to the United States and to step into an airplane.

The trip was basically a group outing -- I was joined by Eelco and many of his PhD students. In addition to my HotSWUp 2008 paper, we also had an OOPSLA paper (about the Dryad compiler), a WebDSL poster, and another paper about the implementation of WebDSL (the paper titled: "When frameworks let you down") to present.

I was surprised to see how many people Eelco knew at the conference. He was also actively encouraging us to meet up with people and bringing us in touch with people that he know that could be relevant.

We were having a good time together, but I also remember him saying that it is actually much better to visit a conference alone, rather than in a group. Being alone makes it much easier and more encouraging to meet new people. That lesson stuck and in many future events, I took the advantage of being alone as an opportunity to meet up.

Working on practical things

Once in a while I had casual discussions with him about ongoing things in my daily work. For my second paper, I had to travel to ICSE 2009 in Vancouver, Canada all by myself (there were some colleagues traveling to co-located events, but took different flights).

Despite the fact that I was doing research on Nix-related things, NixOS at that time was not my main operating system yet on my laptop because it was missing features that I consider a must-have in a Linux distribution.

In the weeks before the planned travel date, I was intensively working on getting all the software packaged that I consider important. One major packaging effort was getting KDE 4.2 to work, because I was dissatisfied with only having the KDE 3.5 base package available in NixOS. VirtualBox was another package that I consider critical, so that I could still run a conventional Linux distribution and Microsoft Windows.

Nothing about this work is considered scientific "research" that may result in a paper that we can publish. Nonetheless, Eelco recognized the value of making NixOS more usable and encouraged me to get all that software packaged. He even asked me: "Are you sure that you have packaged enough software in NixOS so that you can survive that week?"

Starting my blog

Another particularly helpful advice that he gave me is that I should start a blog. Although I had a very good start of my PhD, having a paper accepted in my first month and another several months later, I slowly ran into numerous paper rejections, with reviews that were not helpful at all.

I talked to him about my frustrations and explained that software deployment research is generally a neglected subject. There is no research-related conference that is specifically about software deployment (there used to be a working conference on component deployment, but by the time I became a PhD student it was no longer organized), so we always had to "package" our ideas into subjects for different kinds of conferences.

He gave me the advice to start a blog to increase my interaction with the research community. As a matter of fact, many people in our research group, including Eelco, had their own blogs.

It took me some time to take that step. First, I had to "catch up" on my blog with relevant background materials. Eventually, it paid off -- I wrote a blog post titled: Software deployment complexity to emphasize software deployment as an important research subject, and thanks to Eelco's Twitter network I came in touch with all kinds of people.

Lifecycle management

For most of my publication work, I intensively worked with Eelco Dolstra. Eelco Visser left most of the practical supervision to him. The only published paper that we co-authored was: "Software Deployment in a Dynamic Cloud: From Device to Service Orientation in a Hospital Environment".

There was also a WebDSL-related subject that we intensively worked on for a while, that unfortunately never fully materialized.

Although I had already had the static aspects of a WebDSL application deployment automated -- the infrastructure components (Apache Tomcat, MySQL) as well as a function to compile a Java Web application Archive (WAR) with the WebDSL compiler, we also had to cope with the data that a WebDSL application stores -- WebDSL data models can evolve, and when this happens, the data needs to be migrated from an old to a new table structure.

Sander Vermolen, a colleague of mine, worked on a solution to make automated data migrations of WebDSL possible.

At some point, we came up with the idea to make this all work together -- deployment automation and data migration from a high-level point of view hiding unimportant implementation details. Due to the lack of a better name we called this solution: "lifecycle management".

Although the project seemed to look straight forward to me in the beginning, I (and probably all of us) heavily underestimated how complex it was to bring Nix's functional deployment properties to data management.

For example, Nix makes it possible to store multiple variants of the same packages (e.g. old and new versions) simultaneously on a machine without conflicts and makes it possible to cheaply switch between versions. Databases, on the other hand, make imperative modifications. We could manage multiple versions of a database by making snapshots, but doing this atomically and in an portable way is very expensive, in particular when databases are big.

Fortunately, the project was not a complete failure. I have managed to publish a paper about a sub set of the problem (automatic data migrations when databases move from one machine to another and a snapshotting plugin system), but the entire solution was never fully implemented.

During my PhD defence he asked me a couple of questions about this subject, from which (of course!) I understood that it was a bummer that we never fully realized the vision that we initially came up with.

Retrospectively, we should have divided the problem into a smaller chunks and solve each problem one by one, rather than working on the entire integration right from the start. The integrated solution would probably still consist of many trade-offs, but it still would have been interesting to have come up with at least a solution.

PhD thesis

When I was about to write my PhD thesis, I was making the bold decision to not compose the chapters directly out of papers, but to write a coherent story using my papers as ingredients, similar to Eelco Dolstra's thesis. Although there are plenty of reasons to think of to not do such a thing (e.g. it takes much more time for a reading committee to review such a thesis), he was actually quite supportive in doing that.

On the other hand, I was not completely surprised by it, considering the fact that his PhD thesis was several orders of magnitude bigger than mine (over 380 pages!).


After I completed my PhD, and made my transition to industry, he and his research group relentlessly kept working on the solution ecosystem that I just described.

Already during my PhD, many improvements and additions were developed that resulted in the Spoofax language workbench, an Eclipse plugin in which all these technologies come together to make the construction of Domain Specific Languages as convenient as possible. For a (somewhat :-) ) brief history of the Spoofax language workbench I recommend you to read this blog post written by him.

Moreover, he also kept dogfooding his own practical problems. During my PhD, three serious applications were created with WebDSL: researchr (a social network for researchers sharing publications), Yellowgrass (an issue tracker) and Weblab (a system to facilitate programming exams). These applications are still maintained and used by the university as of today.

A couple of months after my PhD defence in 2013 (I had to wait for several months to get feedback and a date for my defence), he was awarded the prestigious Vici grant and became a full professor, starting his own programming language research group.

In 2014, when I was already in industry for two years, I was invited for his inauguration ceremony and was given another demonstration of what Spoofax has become. I was really impressed by all the new meta languages that were developed and what Spoofax looked like. For example, SDF2 evolved into SDF3, a new meta-language for developing Name Address bindings (NaBL) was developed etc.

Moreover, I liked his inauguration speech very much, in which he briefly demonstrated the complexities of computers and programming, and what value domain specific languages can provide.

Concluding remarks

In this blog post, I have written down some of my memories working with Eelco Visser. I did this in the spirit of my blog, whose original purpose was to augment my research papers with practical information and other research aspects that you normally never read about.

I am grateful for the five years that we worked together, that he gave me the opportunity to do a PhD with him, for all the support, the things he learned me, and the people who he brought me in touch with. People that I still consider friends as of today.

My thoughts are with his family, friends, the research community and the entire programming languages group (students, PhD students, Postdocs, and other staff).