General talk about software patterns

[Pascal Costanza <pc AT p-cos.net>]

Dynamic Languages Day @ Vrije Universiteit Brussel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Monday,  February 13,  2006,  VUB Campus Etterbeek

The VUB (Programming Technology Lab, System and Software Engineering  
Lab), ULB (deComp) and the Belgian Association for Dynamic Languages  
(BADL) are very pleased to invite you to a whole day of presentations  
about the programming languages Self, Smalltalk and Common Lisp by  
experts in these languages. Besides some introductory material for  
each language, the reflective facilities in the respective  
programming environments will be highlighted. The presentations will  
be especially interesting for people with good knowledge about  
current mainstream object-oriented languages like Java, C# and C++  
who want to get a deeper understanding about the expressive power of  
Self, Smalltalk and Common Lisp. In order to prepare the ground for  
these presentations, Professor Viviane Jonckers will introduce the  
day by an overview of the benefits of teaching dynamic languages to  
undergraduate students in computer science. She will especially  
discuss the specific advantages of using Scheme as an introductory  
language instead of the more widely employed Java language.

Attendance is free and open to the public. Please make sure to  
register for the event by sending an e-mail to Pascal Costanza  
(pascal.costanza AT vub.ac.be), so we can plan ahead. The number of  
places will be limited according to the exact location of the event  
and will be allocated on a first-come, first-serve basis. Watch the  
website for the exact schedule, location and any news at http:// 
prog.vub.ac.be/events/2005/BADL/DLD/dld.html.

Abstracts of the Talks
~~~~~~~~~~~~~~~~~~~~~~

Scheme as an introductory language (Viviane Jonckers)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The VUB has a rich history in dynamic programming language teaching  
and research. Ever since the late 80's, compulsory courses on Lisp  
and Smalltalk have played an important role in the last two years of  
the computer science curriculum. Since the early 90's, this role was  
further intensified by selecting Scheme as the introductory course in  
the first year and by promoting Scheme as the lingua franca for most  
courses in the first two years. Professor Jonckers' introductory talk  
to the dynamic languages day explains how this early exposure to the  
dynamic paradigm is the seed that gives students the skills to fully  
grasp and appreciate the more advanced dynamic paradigms (such as  
Lisp, CLOS, Smalltalk and Self) in subsequent courses of their  
computer science training.

Self (Ellen Van Paesschen)
~~~~~~~~~~~~~~~~~~~~~~~~~~

Self is a prototype-based object-oriented programming language where  
everything is an object and all manipulation of objects is initiated  
through message sending. A prototype-based language eschews classes  
and allows object creation ex-nihilo or by cloning prototypes. Self  
resembles Smalltalk in both its syntax and semantics. Other  
characteristics of Self are delegation (object-centered inheritance),  
parent sharing and child sharing (multiple inheritance), and dynamic  
parent modification. Further the Self environment includes a powerful  
mechanism for reflective meta-programming based on mirror objects.  
The Self group were also the first to introduce traits objects that  
gather shared and reusable behavior between objects in order to  
program in a more efficient and structured way.

After a brief introduction to the highly interactive Self environment  
the language's basics and its syntax and semantics are presented.  
Next the most important advanced features such as mirrors and dynamic  
parent modification are illustrated.

Smalltalk (Johan Brichau, Roel Wuyts)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Smalltalk is class-based object-oriented programming language.  
Everything in Smalltalk is an object and these objects communicate  
through messages. The Smalltalk language itself offers only very few  
programming constructs and is thus easy to learn and grasp.  
Therefore, the expressive power of Smalltalk lies in its huge library  
of frameworks, which includes an extensive metaobject protocol that  
enables powerful dynamic (runtime) reflection. Furthermore, perhaps  
one of the most significant advantages of Smalltalk outside of the  
language itself is that software development is a truly dynamic  
experience. The Smalltalk environment features the incremental  
development of an application where there is no strict separation  
between development and execution cycles, leading to an interactive  
and dynamic development process.

Besides a short introduction to the Smalltalk programming language,  
this presentation will focus on the dynamic reflective facilities of  
Smalltalk. We will demonstrate the power of its metaobject protocol  
through a number of tools that extensively rely on it. Furthermore,  
we will provide some insight in the dynamic nature of Smalltalk  
development through a live demonstration.

Generic Functions and the CLOS Metaobject Protocol (Pascal Costanza)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Common Lisp Object System (CLOS) is unique in two ways.

* In most OOP languages, methods belong to classes and are invoked by  
sending messages. In CLOS, methods belong to generic functions  
instead of classes, and those generic functions select and execute  
the correct method according to the types of the arguments they receive.

* The CLOS Metaobject Protocol (MOP) specifies how its essential  
building blocks are to be implemented in CLOS itself. This allows  
extending its object model with metaclasses that change important  
aspects of CLOS for a well-defined scope.

This presentation introduces these two notions. The code for an  
interpreter for generic functions that performs selection and  
execution of methods will be developed live during the presentation.  
This will be followed by a discussion how that code can be extended  
to introduce, for example, multimethods and AOP-style advices, and a  
sketch how generic functions are implemented efficiently in the  
"real" world. In the second part, the extensibility of the CLOS MOP  
will be illustrated by implementing - live - the (hashtable-based)  
Python object model as a metaclass. Other practical extensions based  
on the CLOS MOP are also sketched, like object-relational mappings,  
interfaces to foreign-language objects, and domain-specific  
annotations in classes.


Biographies
~~~~~~~~~~~

Viviane Jonckers received a master degree in Computer Science from  
the Vrije Universiteit Brussel in 1983 and a Ph.D. degree in Sciences  
from the same university in 1987. Since 1987 she is a professor both  
in the Computer Science Department of the faculty of Sciences as in  
the Computer Science group of the Engineering Faculty. Currently, she  
is the director of the System and Software Engineering Lab. Her  
current research interests are in integrated software development  
methods with a focus on component based software development and  
aspect oriented software development. She participated in and has  
been project manager of several national and international R&D projects.

Roel Wuyts is professor at the University Libre de Bruxelles, where  
he leads the deComp group. His fields of interest are logic meta  
programming, forms of reflection and language design. On the side he  
also dabbles in development environments. Quite a lot his development  
is done in Smalltalk, extensively using the reflective facilities in  
that language to do research in language symbiosis, development  
environments and for rapid programming in gneral. From the moment he  
realized that dynamicity was what he really liked in all of his  
favourite programming languages (Smalltalk, Prolog and Scheme), he  
has been trying to grow the dynamic languages field again. Part of  
this endavour was the organization of the first Dynamic Language  
Symposium, a symposium co-organized with OOPSLA'2005 in San Diego.

Johan Brichau currently holds a postdoc position at the Laboratoire  
d'Informatique Fondamentale de Lille (LIFL). He is also associated  
with the Programming Technology Lab at the Vrije Universiteit  
Brussel, where he obtained a Ph.D. degree in Computer Sciences in  
2005. Johan's research is focusing on the use of metaprogramming in  
the context of generative programming techniques and aspect-oriented  
programming languages. To this extent, he has been extensively using  
the Smalltalk metaobject protocol for the creation and development of  
(generative) logic metaprogramming techniques as well as aspect- 
oriented language extensions to Smalltalk.

Pascal Costanza has a Ph.D. degree from the University of Bonn,  
Germany. His past involvements include specification and  
implementation of the languages Gilgul and Lava, and the design and  
application of the JMangler framework for load-time transformation of  
Java class files. He has also implemented ContextL, the first  
programming language extension for Context-oriented Programming based  
on CLOS, and aspect-oriented extensions for CLOS, which all heavily  
rely on the CLOS MOP. He is furthermore the initiator and lead of  
Closer, an open source project that provides a compatibility layer  
for the CLOS MOP across multiple Common Lisp implementations.

Ellen Van Paesschen obtained a master degree in computer science at  
the Vrije Universiteit Brussel in 2000. Currently she is a Ph.D.  
student at the Programming Technology Lab. Ellen's research is  
focusing on using dynamic and prototype-based languages for model- 
driven development and round-trip engineering (RTE). She has created  
a research prototype of a dynamic prototype-based RTE environment in  
Self which is the main implementation language in her research. This  
environment differs from other existing tools at the level of  
synchronisation, run-time objects and constraint enforcement steered  
from an analysis model. Her other interests include (the analysis  
phase during) software engineering and role modelling.

--
Pascal Costanza, 
mailto:pc AT p-cos.net,
 http://p-cos.net
Vrije Universiteit Brussel, Programming Technology Lab
Pleinlaan 2, B-1050 Brussel, Belgium