Self on Smalltalk
Due to the simplicity of Self, it should be no problem to implement it from
scratch. At one hacking session, which took place around Munich
in October 1995, I started an implementation of Self from scratch with Smalltalk/V.
This code was later released (see the corresponding README file ) and
extended by Stefan Matthias Aust to run on VisualWorks a.k.a. Cincom Smalltalk
(see his homepage for
more details). This implementation is kind of nice because it integrates Self
objects seamlessly with Smalltalk objects.
On the downside, this implementation is purely interpreted, and therefore
much slower than the compiled one. In addition, the vast amount of software included
in the Self system released by Stanford University and Sun (e.g. the Morphic
GUI, the Mango parser generator, the Smalltalk subsystem) heavily uses Unix library
infrastructure, which is not available in Smalltalk in this form. However, Stefan
Matthias Aust got the implementation to process core/systemStructure.self and
core/coreObjects.self of the original Self system.
A Self Parser in Yacc/Lex
I also started a parser for Self using lex and yacc. However, I ran into trouble
since the language definition has some delicate features. Firstly, a
dot '.' can be used both as statement separator and resend designator. Secondly,
parentheses '()' can mean constructors of objects, as well as operator precedence,
depending on the context.
The End of the Green Project
When Sun dumped Self in favor of Java, it became a little quiet about the
Self group. The Self homepage sometimes appeared and sometimes disappeared, and
for very short periods of time the source code of the Self system was available
on the Self homepage.
At one of these occasions, I downloaded this source code (Release 4.0), released
under BSD license, and stored it on my hard-disc. This was around 1995, and it
took quite a long while until I took the time to have a look at it.
This code is highly optimized to SPARC as target architecture, and fortunately,
I did not know that the Self community considered it impossible to port the system
to another architecture than SPARC. :-)
My Winter Vacation 1999
From winter holidays 1998 till the end of January 1999, I had a few weeks of vacation
to spend. Since my former fiancée had
to learn for her university tests, I took these 5 weeks to dig into the Self
code. Somehow, I was not amused by the imagination of having to program in C++
only all my life.
It took me the first two weeks to figure out and fix a quite stupid memory
leak in the Self build system (makeDepsAndIncs). After that, the whole system
compiled under Linux quite nicely, except that is was still compiling and jumping
to SPARC binary code.
Another challenge was the Unix signal stacks that Self uses to implement its
multi-threading. The Linux kernel 2.0 which I was working with did not fully
implement these signal stacks (see define 'SIGNAL_STACKS_AVAILABLE' in Self4Linux-0.1.0.tar.gz).
Fortunately, I had the source code of the kernel and of C runtime library available,
so I could plainly see what was going on.
The next step was the setup of an i386 assembler and to make all the various
places in the Self compiler emit x86 code. After trying several alternatives,
I stuck to the robust way of wrapping the machine specific part of gas into the
Self kind of OO shell. This approach is somewhat slower than the Sparc
one because if uses virtual functions for the operand classes. In addition, the
gas code is GPL, so the whole system had to be release under GPL, too. It is
still an open project to create a faster assembler from scratch.
Middle of January, I announced my work in the self-interest mailing list,
and I got a lot of support by various people. Most notably, Mario Wolczko sent
me a manual of the SPARC instruction set, which made it easier for me to figure
out what the original Self system was supposed to do (I didn't have any way to
run the original Self on SPARC by that time).
End of January 1999, I release the first version of Self. It was running on
Linux and was able to perform simple message passing. Because of the stack problems,
blocks did not work yet, the garbage collector could not walk the stack, and
the multi-threading did not work.
The Final Steps
A MacOS version of Self running on PowerPC was brought out by David Ungar
in October 31 of 1999 (see Self
This version contained a portable stack frame architecture.
Thorsten Dittmar and Maximilian Thiel wrote a GPL-free new implementation
of the i386 assembler. We conducted a Self-Hacking-Session on January 8th 2000
in Witten, Germany. On this occasion, we ported my changes to Self 4.0 to the
new release of 4.1.
Maximilian Thiel was working on it for a while, and in July/August he spent
a few weeks in Munich with me in which we got pretty close to getting the GUI
up and running. However, we didn't find all bugs in the new assembler. Since
I had to go to Dresden to pursue my Ph.D., I could not work on it further.
Independently, Harald Gliebe merged
the i386 code generation of me with the portable stack frame of David and made
the GUI running December 2001 using my gas assembler framework. In addition,
he also got to run it on Microsoft Windows using Cygwin, and made various other