As an ArgoUML contributor I'm going to blog my activities here, so that they may draw interest by other developers or help other developers when doing tasks similar to what I've done. AND(!) the grand vision that makes an Argonaut what he is, TO THRIVE IN THE BIG DANGEROUS WORLD, TAKING THE Argo TO A GOOD SHORE ;-))

Friday, May 07, 2010

3rd European Lisp Symposium, day 2

Tutorial: Parallel Programming in Common Lisp by Pascal Costanza

09:00 - 10:30

Parallel programming is the wave of the future: It becomes harder and harder to increase the speed of single-core processors, therefore chip vendors have turned to multi-core processors to provide more computing power. However, parallel programming is in principle very hard since it introduces the potential for a combinatorial explosion of the program state space. Therefore, we need different programming models to reduce the complexity induced by concurrency.

Common Lisp implementations have started to provide low-level symmetric multi-processing (SMP) facilities for current multi-core processors. In this tutorial, we will learn about important parallel programming concepts, what impact concurrency has on our intuitions about program efficiency, what low-level features are provided by current Common Lisp implementations, how they can be used to build high-level concepts, and what concepts Lispers should watch out for in the near future. The tutorial will cover basic concepts such as task parallelism, data parallelism and pipeline models; synchronization primitives ranging from compare-and-swap, over locks and software transactional memory, to mailboxes and barriers; integration with Lisp-specific concepts, such as special variables; and last but not least some rules of thumb for writing parallel programs.


I questioned Pascal about the portability of parallel code and there is none up-to-now. This smells like an opportunity.

On a question of mine about the need to sync the functional data structures internally - for instance FSet is portable - I got a book reference: Purely functional data structures - it was suggested to me that I should read this to understand why there is no need for synchronization. THOUGHT: my lack of an academic background in computer science is to blame for my lack of knowledge about things like this, even after having read about it in respect of the Clojure data structures.

Session III (The Language)

11:00 - 12:45

CLoX: Common Lisp Objects for XEmacs by Didier Verna

Debugging CLoX is a living hell.

Didier made an excellent and very dynamic presentation. There should be no problem in moving what he got up-to-now into GNU Emacs. He intends to optimize some parts to C, though, and then it would be a problem, because XEmacs C level is incompatible with GNU Emacs C.

CLWEB: A literate programming system for Common Lisp by Alexander Plotnick

CLWEB is language specific with advantages for Common Lispers. No tracking back to the source file position yet. Complexity due to the different objectives of the CLWEB reader and Common Lisp reader. Common Lisp STREAM libraries and pretty printer are great! Code walker for Common Lisp - based on the one from the macro-expand-all paper(?). It would be nice if there was more standard ways to interact with the Lisp operators, as to have an easier time creating a walker. Works in SBCL, Allegro and another (Clozure ?).

Keynote: Lots of Languages, Tons of Types by Matthias Felleisen, Northeastern University

Since 1995 my research team (PLT) and I have been working on a language for creating programming languages - small and large. Our code base includes a range of languages, and others contribute additional languages on a regular basis. PLT programmers don't hesitate to pick our lazy dialect to implement one module and to link it to a strict language for another module in the same system. Later they may even migrate one of the modules to the typed variant during some maintenance task.

An expressive macro system is one key to this riches of languages. Starting with the 1986 introduction of hygienic macros, the SCHEME world has worked on turning macros into tools for creating proper abstractions. The first part of my talk will briefly describe this world of modern macros and its key attributes: hygiene, referential transparency, modularity of macros, phase separation, and macro specification.

The second part of my talk will focus on how to equip LISP-like languages with a sound type systems and that will illustrate the second key idea, namely, monitoring the interactions between different languages. Our approach to type systems allows programmers to stick to their favorite LISP idioms. It mostly suffices to annotate functions and structures with type declarations during maintenance work. To ensure the soundness of this information even when higher-order values flow back and forth between typed and untyped modules, module boundaries are automatically equipped with software contracts that enforce type-invariants at all levels.

PLT Scheme is now Racket. Types are very important for maintenance work.

Type theory is stupid. Design driven to make typed Lisp programming practical. Combining the macro system and the type system is still an unresolved challenge.

Panel – does Lisp matters?

I'm part of the panel and therefore instead of notes the following is what I prepared to say. Eventually the specifics weren't followed...

My small intervention notes

  1. Name
  2. disclaimer: less Lisp Experience than the majority of the persons in the room. Although I'm a SISCOG employee, what I will say represents my opinions and I don't know if they are aligned with the ones of SISCOG administration or with the ones of the majority of SISCOG employees.
  3. background:
    1. Physics Engineering, some experience in software development both for data processing and analysis and for scientific instruments
    2. then I started working as a software engineer in telecommunications domain, specifically, in the management of telecommunications networks
    3. about 3 years ago I joined SISCOG and started working in the railway planning and management domain and yes, programming in Common Lisp.

So, SISCOG was founded by 2 professors of the IST - an engineering academical institution. They wanted to use Artificial Intelligence and in the 80s that meant Lisp.

Question: Does Lisp matters?

Yes it does, because of the following three things:

  • Inspiration – it has been an inspiration to lots of persons and languages. This is nothing new, but, many of the new languages still steal from Lisps. And normally they are still crippled copies. So Lisp matters even if it didn't existed anymore, although with open source, as Kent Pitman said yesterday, it isn't possible to kill it.
  • Edge – it provides an edge for its users. Be it due to its dynamic nature, macros, tools, history, smart people magnet, etc.
  • Research – Lisp is very important due to its flexibility and ease of experimenting with new ideas. I will just refer as an example to the previous keynote by Matthias Felleisen.

Quote by Matthias Felleisen:

we are the cockroaches of the world, nobody can kill us!

Announcements, Symposium wrap-up

Didier Verna announced that the 4th European Lisp Symposium will be next year in Hamburg, Germany, on March 30 and April 1. Deadline to submissions will be around the end of the year. This time around I will try to have something to present. Theme parallelism and ...

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