12/24/2006
What is Smalltalk?
Where is the
Editor? Where is the Compiler? How can I compile and run a program?
Forget for a
while about Smalltalk as a programming language. Avoid, for a while,
comparing it
with other programming languages and their tools. We are going to talk
about
something pretty different.
What is
Smalltalk? Smalltalk is a different kind of computer. One that is not
based on
the concept of program.
But wait a
minute, doesn’t Smalltalk run on regular computers? Yes, it
does. But Smalltalk
lets you forget about a CPU that loads programs from disk to RAM, in
order to
execute them and such.
With Smalltalk,
your computer becomes a virtual place filled with things. You can
interact with
these objects, and ask them to perform actions. You can inspect them,
and study
their behavior and relationships. Of course, you can also modify their
behavior
and relationships.
Everything in
Smalltalk is an Object. For example, the Numbers and
Characters. But also the Editor and the Compiler are Objects.
The windows and menus, with their scrollbars and buttons and stuff are
Objects
too. Pieces of code are also Objects. In Smalltalk, even True and False
are
objects.
Most computers
run Operating Systems. But the entities of regular Operating Systems
are not
uniformly available for inspection, study and modification. This would
break
the basic ideas of Smalltalk! Therefore, while in Smalltalk, Smalltalk
becomes
the Operating System. You can interact with and modify such things as
Files and
Directories the same way you manipulate any other object.
As the whole
Smalltalk system is made with Objects, and all Objects can be studied
and
modified, the Smalltalk system hides no secrets from the user. Any
aspect of
the system can be modified to suit the user needs.
To continue, you
need a Smalltalk system. Let’s use Squeak. You can go to http://www.squeak.org/Download
and get Squeak for
your platform. The set of all the available object in a certain
Smalltalk
environment is called the ‘image’. The standard
Squeak image includes really a
lot of objects. Perhaps too many for a beginner. You can use it anyway,
or you
can get www.jvuletich.org/Squeak/EToysFreeMorphic/NoEtoysImage-jmv.zip.
This is a reduced image I like to use.
Launch Squeak.
Click on an
empty area of the screen to open the World menu. Select
‘Open…’ /
‘workspace’.
There type 3+4. Select it. Right click over it and select
‘print it’. If it
shows 7, you have written your Smalltalk “hello
world” program.
Now you can try
the first Smalltalk example in The
Weekly Juan #6.
Copy and paste the code in an empty workspace. Now select it and right
click
‘do it’. Voila. It works.
Now let’s
try
the second version. This one includes some real Smalltalk programming.
This is,
adding behavior to existing objects. We’ll add new behavior
(methods, code) to
FFT objects. This is done by modifying the FFT class. In Smalltalk all
objects
belong to some class, that defines its behavior. Please note that
classes are
Objects too (as everything else).
Open the world
menu and select ‘Open’ /
‘browser’. What you see now is the Smalltalk
browser. The
main tool for reading and writing Smalltalk code. The top half of the
browser
has four lists. From left to right we have:
- The System
Categories. The items here show groups of classes that belong together.
Do as
follows: Right click / ‘find class…’ FFT
<Enter>. The other 3 lists get
filled.
- The
Classes in
the selected Category. Class FFT is now selected.
- Method
categories. Methods in a class are grouped together in method
categories. You
can create a new category if you wish, named for example
‘extras’.
When you
select
a category, in the bottom half of the browser you see a method
template.
Replace the selected text with the magnitudes method. Right click /
‘accept’.
We have added a new method to the class. Add the remaining 4 methods.
All the methods
appear in the fourth list, the methods list.
Now you can try
the second Smalltalk example, that uses the newly added methods. Do it
in a
workspace as before.
After this, you
can use the browser to see what other classes are available. Some of
the most
interesting objects in Squeak are graphical objects,
‘Morphs’. Read about them!
Read my introductory
article on
Morphic.
You can also
check the other links below Other Squeak Projects in http://www.jvuletich.org/.
If you want to
better understand the ideas, read http://users.ipa.net/~dwighth/smalltalk/byte_aug81/design_principles_behind_smalltalk.html.
In Spanish at http://www.smalltalking.net/Papers/stDesign/stDesign.htm.
Other great links
for beginners are:
http://www.squeak.org/
http://www.iam.unibe.ch/~ducasse/FreeBooks.html
http://en.wikipedia.org/wiki/Smalltalk
http://kb.iu.edu/data/aeya.html
http://www.webopedia.com/TERM/S/Smalltalk.html
http://www.whysmalltalk.com/articles/collins/what.htm
http://www.smalltalk-central.com/showDocument.ssp?section=Articles&name=What%20is%20Smalltalk%3F
To know more
about the history of Smalltalk, read
http://gagne.homedns.org/~tgagne/contrib/EarlyHistoryST.html
http://www.parc.xerox.com/about/history/default.html(at
the bottom of the page, the seventies).
Well, I hope you
enjoyed this, and you are wanting to know more about Smalltalk!
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