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Abstract

Much of the examples here apply equally well to all implementations of Smalltalk. Though all implementations of Smalltalk share the same basic characteristics, there are differences among them - especially when GUI code comes into play. There's a number of freely available¹  Smalltalk implementations available for Linux: GNU Smalltalk, Smalltalk/X, Squeak, and VisualWorks Non Commercial².  Squeak in particular is doing some really cool stuff lately, but the examples here are written in VWNC, since this is the flavour that I'm most familiar with.  Also, even though there's a later version available, I'm going to use VWNC v3.0 for illustrative purposes since that is the version with the most freely available tools/extensions available.

This article covers some background information on Smalltalk, getting and installing VWNC3, characteristics of Smalltalk (with examples), and further references. The characteristics of Smalltalk that are covered here are that it:

• is a pure OO environment, encourages OO programming
• can save exact state of the IDE
• is a literate language
• is incrementally byte-compiled
• is a portable environment; write once, run anywhere (virtual machine/ GUI)
• can inspect and manipulate objects in real time
• has a large degree of reflectiveness (start with running app, extensions)
• has garbage collection, no explicit pointers

1.0 Background Information

Smalltalk has been around for quite a while, it originated at the Xerox Palo Alto Research Center (PARC) in the early 70s, and its original intention was to provide an environment for children to start learning how to program in.  Accordingly, its syntax is very simple and it's a very mature environment.  Smalltalk's power is rooted in its large class library, which can be a double-edged sword.  You don't have to keep reinventing the wheel to get any work done, but on the other hand you spend a lot of time looking for the right wheel to reuse when you're first learning it⁴.

Another double-edged sword is that it's a pure OO environment, and thus encourages people to make the paradigm shift to OO much more strongly than other Object Based (OB) languages⁵  (more on this later).  People who make the shift tend to become very attached to Smalltalk and find it a very fun, productive⁶, and theoretically pure environment to work in.  People who don't make the shift tend to shun it, and stay in OB languages where it's easier to get away with writing procedural code in the guise of writing OO code. (No Dorothy, just because you're using a C++ compiler doesn't mean that you're writing OO code).

Though many people characterize Smalltalk as only being useful in large, vertical markets, Smalltalk is extremely flexible in that it is also used in very small, horizontal markets.  Smalltalk has been used to write applications⁷ for large network management systems, to hospital clinical systems, to palm pilots, to micro controllers, to embedded firmware.

But that's enough background information, let's get on with some real examples.
 

2.0 Installation Stuff

To start it up, I like to copy the virtual machine to the image directory, or to make a symbolic link.  Since I have it installed on my dos partition, I'll make a copy:
    cp /dos/vwnc3/bin/linux86/visualnc /dos/vwnc3/image/visualnc
I noticed that the virtual machine isn't executable by default, so let's make it that way:
    chmod 555 visualnc
Then to start the image, it's necessary to tell the virtual machine what image to run, do:
    cd /dos/vwnc3/image
    visualnc visualnc.im
A license reminder screen pops up every time you start VWNC, click I accept, and proceed through it.  The window that appears on top is called the Transcript, and the window below it is called a Workspace.  Next, you need to inform the image where to find its needed system files.  To do this, click on File>Set VisualWorks Home from the Transcript.  In the dialog that appears, enter in the home directory:  /dos/vwnc3.

The Transcript and Workspace look like:

Fig. 1 - VWNC Transcript

Fig. 2 - Default VWNC transcript

The startup workspace has some useful information that's worth reading, but it isn't necessary to read it to continue through this article.

A note on mice:  Smalltalk assumes that you have a three button mouse.  If this isn't the case, you can simulate a three button mouse on a two button mouse by clicking both the left and right buttons at the same time.

3.0 Some Notable Characteristics of Smalltalk

3.1 Saving your work

Lets give saving a try (might as well save the system file location you just specified). Move your windows around until they're where you like them, then save your image, select File>Save As... It's a good idea to save your image as something other than the virgin image, so if you run into problems you can always return to the clean image and reload your code.  I'll save the image as testingImage. After saving, try closing the image File>Exit VisualWorks...>Exit.  Then to restart, be sure to pass the new image name to the virtual machine.  Note, that when you save your image, the date and time are printed on the transcript, like so:

Fig. 3 - Transcript after saving as 'testingImage'

3.2 Everything is an object

Ex 1: Hello World

• Open a new workspace (click on Tools>Workspace)
• In the workspace, type: Transcript cr.  Transcript show: 'Hello World.'
• Congratulations, you just wrote your first Smalltalk code.  Now let's see it work:
• Highlight that line of code, middle click and select do it (This evaluates the Smalltalk code you just wrote)
• You should see the 'Hello World' text be printed in the Transcript:


Fig. 4 - Hello World example
• Let's examine the Smalltalk code:

 

Transcript cr.	This code gets a hold of the Transcript object, and asks it to show a carriage return on itself.
Transcript show: 'Hello World.'	Gets a hold of the Transcript object, and asks it to show 'Hello World' on itself

• You can also print 'Hello World' to the command line, open a new window and print 'Hello World' on it, or design a GUI and put 'Hello World' on it.  But again for the sake of brevity, we'll move on.
• cr is a message to Transcript, just as show: is a message to Transcript too.  They're just messages that Transcript knows how to respond to.  They're not part of Smalltalk syntax.
• The above point is important to remember for the non-OO programmers out there, we send messages to objects to ask them to do something.

Ex 2: Displaying current date

• In your opened workspace, type:  Date today
• Highlight that line of code, middle click and select print it (This evaluates the Smalltalk code you just wrote, and prints out the result.)
• You should see the current date printed, like:


Fig. 5 - Printing Date today

 

Date today

Asks the class Date what the date today is

• Ok, let's get a better look at what Date today is evaluating to.  Highlight that line of code (without the date that was printed), middle click and select inspect it.  You should see:


Fig. 6 - An inspector on a date
• This is called an inspector (This too is an object BTW).  Inspectors are objects that allow you to have a peek at objects.  If you click on self in the inspector, you'll see a textual representation of the date:


Fig. 7 - Inspector showing textual representation of the date
• Look familiar?  That's because in Fig. 5, when you printed the Date today, you were really printing a textual representation of the Date object.  If you click on the two other attributes of this date, you'll see that day keeps what day number it is within the year (1->365, usually), and year keeps what year the date is for.
• All objects have a textual representation, even if it's just the type of object it is (though that isn't very useful).
• The inspector is a very powerful concept.  Realize that you just asked Date for the current date, and you got a hold of a date object.  You can not only peek around this date, but you can also work with it and modify it.  For example, click on day, and enter in n+1 for what is there.  In Fig 7, Feb 6 is the 37th day of the year, so I'll enter in 38.  Then middle click, and choose accept.  You'll notice that it appears that nothing has changed.  But what you've done is to now set the object to represent the date for the n+1th day of the year.  Now, if you click back to the self on the date, you'll see it's now showing a date for one day later than what the current date is:


Fig. 8 - Inspector showing date after current date

Another thing to notice is the literateness of Smalltalk.  To get the date today we just asked Date for today.  Though Smalltalk is a very literate language, it obviously has to break down somewhere, for example, we can't ask Date for tomorrow.  That being said though, the general syntax of Smalltalk is very simple and easy to read.  Keep this in mind while looking through the upcoming code examples.

Let's move on to the third example of this section then, and get into the paradigm shift aspect of OO:

Ex 3: Illustrating the paradigm shift

• In your workspace, type: 1 + 2 * 3
• Now, before you evaluate this code, think about what the answer is going to be.  You're probably thinking 7.  Well, highlight the line of code and print it
• You'll notice the answer is 9:


Fig. 9 - Result of message send
• It's funny how many non-OO programmers go running in tears after I show them this.  "What!  No operator precedence, what a foul language!  I'm going to stick to C++ because I can understand it!"  Seriously, I've had it happen many times.
• However, reality depends on the blinders you're wearing; when I wrote the answer above, I first thought of writing 9, because I was thinking in an OO mindset, not a procedural mindset.
• The reason this is the case, is because (repeat after me) everything is an object.  In this example, the numbers 1, 2, and 3 are all objects.  The operators: + and * are just messages that are being sent to objects.  The reasoning is that if + and * are just messages, why should they have precedence over other types of messages?  All messages of the same type are treated equal in Smalltalk.
• To see for yourself, highlight 1, middle click, and choose inspect.  You'll get an inspector on SmallInteger, which is the type of object that the object 1 is.


Fig. 10 - Inspecting the object 1
• So, the code is evaluated as:
• (the number 1) is asked to do (+) with (the number 2)
• (the number 1) does this, answers the object: (the number 3)
• (the number 3) is asked to do (*) with (the number 3)
• (the number 3) does this, answers the object: (the number 9)
• To get the code to evaluate as a procedural mindset would expect, you can use brackets: 1 + (2 * 3)
• "OK, why can't I highlight the date I printed, February 6, 2000, and inspect that to see the date object?"  Good question.  The simple answer is that there are certain types of objects that can be brought into being (instantiated) by just inspecting a textual representation of them, and there are certain types of objects that can't.  Integers are one of those types of objects that can be instantiated by inspecting a textual representation of them.

4.0 Incremental byte compiling

1. the Smalltalk compiler translates the Smalltalk code into byte codes
2. the byte codes are passed to the virtual machine for execution
3. the byte codes are executed, and the result is returned

1. the Smalltalk compiler translates the Smalltalk code into byte codes
2. the byte codes are kept with that class
3. when a message is sent to a class, the appropriate byte codes for the method are sent to the virtual machine for execution
4. the byte codes are executed, and the result is returned

Java is similar in the respect that it is byte compiled, but different in the respect that it isn't incrementally byte compiled.  So when Java programming, you need to recompile all of it (or parts of it if you're using make), and relink all of it every time you want a change to take effect.
 

5.0 Virtual Machine/Portability

Fig. 11- Selecting a Mac look-n-feel

Fig. 12 - Transcript with Mac look-n-feel

6.0 Reflectiveness

Ex 4: Adding inspect menus to all windows

• Remember when I said that the Transcript and default workspace were objects?  We should be able to inspect them then right?  Right.  However, it's not that easy in the environment as it comes to grab hold of an arbitrary window to inspect it.  We're going to add a simple extension that allows for this.
• Open a class browser Browse>All Classes
• You now see what is called the class browser, or System Browser.


Fig. 13 - Empty class browser
• Going through the panes from left to right, top to bottom, you see: categories, classes, protocols, methods, and method code.  Additionally, you'll see two radio buttons: one sets the browser to look at the instance side of a class, the other sets the browser to look at the class side.  (We're going to do one instance method and one class method.)
• Middle click on the category pane, and select Find Class..., then enter StandardSystemController in the dialog that pops up
• After the browser highlights the StandardSystemController class, click on the menu messages protocol in the protocol pane, and on the back method in the method pane.  You should now see:


Fig. 14 - Class browser with method selected.
• Briefly, categories are groups of classes, we have the Interface-Framework category selected.  We also have the StandardSystemController class selected.  Protocols are groups of methods, and we currently have the menu messages protocol selected.  Methods are where the code is implemented, and we have the back method selected.
• We're going to add a method to the menu messages protocol. To do this, just highlight all of the current method and delete it.  Don't worry, the method isn't gone and won't be deleted by doing this.  It's just an easy way to create a new method in the currently selected protocol.
• Then type in the text:

inspectView

    self view model inspect.

• Then to save the method, middle click and choose accept.
• You'll notice that the method you just entered is now showing in the browser.  It's already been compiled and is ready to be executed.  You should see:


Fig. 15 - Added inspectView method
• Next, we need to add a class side method.  Click on the class radio button in the class browser.
• Then click on the class initialization protocol, and on the flushMenus method.
• Just as before, delete all of the text for the method, (the flushMenus method won't be deleted), and type:

initializeForAdditions
 "Initialize the menu."
 "self initializeForAdditions"

 ScheduledBlueButtonMenu :=
  Menu
   labels: 'relabel as...\refresh\move\resize\front\back\collapse\close\inspect' withCRs
   lines: #(1 7 8)
   values: #( #newLabel #display #move #resize #front #back #collapse #close #inspectView).

• After you're done typing this, middle click and accept the method.  Now you should see:


Fig. 16 - Added initializeForAdditions method
• OK, now comes the neat part.  Right click over the method code pane, you should see the window menu:


• At this point, the code has been byte-compiled.  But, since it's initialization code, it hasn't been run yet.  We can run this code right from the browser; just highlight the self initializeForAdditions text, middle click, and do it.
• Now that the code has been run, you should see inspect added to the bottom of the window menu:


• Now we can inspect any window that has this menu window defined on it.  Try it out by inspecting this class browser we've been using.  Just right click, and choose inspect.  You'll see an inspector on the class browser, selecting the className attribute, you'll see the class there matches the current class selected:

7.0 Garbage Collection

Garbage collection: AKA the sanity saver.  Smalltalk has garbage collection, which means objects that are no longer referenced are cleaned up to free up memory.  I remember pulling out my hair many a time when programming in C++ trying to find memory leaks.  This is because in C++ it's up to the developer to manage your memory.  If you didn't deallocate the memory you're using, your application would continually take up more memory until your machine ran out of memory and crashed.

Speaking of machines crashing, you'll note that we never had to do any pointer manipulation.  This is because Smalltalk has no pointers.  (Well, this is technically incorrect.  Every variable reference is actually a pointer to an object, it's just that in Smalltalk the developer is relieved of the burden of manually maintaining pointers).
 

8.0 Summary

• is a pure OO environment, encourages OO programming
• can save exact state of the IDE
• is a literate language
• is incrementally byte-compiled
• is a portable environment; write once, run anywhere (virtual machine/ GUI)
• can inspect and manipulate objects in real time
• has a large degree of reflectiveness (start with running app, extensions)
• has garbage collection, no explicit pointers

• the online help
• debugger
• numbers - (try printing 100000 factorial in a workspace (if you have the time for crunching - number size is only limited by your memory), or try inspecting 12/7)
• parcels - a code sharing mechanism
• Refactoring Browser - my favourite programming tool
• HotDraw - a reusable draing framework
• testing frameworks - automate your testing
• dynamic changing of widgets at runtime

Glossary

Further References

1. A history of Smalltalk
2. A brief history of Smalltalk
3. GoodStart
4. WikiWikis:
1. Smalltalk
2. Squeak
3. VisualWorks
5. Newsgroup:  comp.lang.smalltalk
6. Free Smalltalk archives:
1. Smalltalk (UIUC - the granddaddy of Smalltalk archives)
2. Squeak
3. VSE (in German)
7. Tutorials:
1. Squeak
2. VisualWorks
8. Lots 'o Smalltalk Links
9. Dave's Smalltalk FAQ (There's a number of ones out there, but even though it's dated, this is the best IMHO.  Dave - it'd be great if you ever got time to finish this.)
10. eXtreme Programming (Which originated in a Smalltalk project)

Footnotes

1. Every implementation has different license restrictions.  To my knowledge, only GNU Smalltalk  and Squeak have GNU copyleft types of licenses.
2. The last two implementations are the newer ones.
3. In article: http://x37.deja.com/getdoc.xp?AN=564595555&CONTEXT=949863157.89849870&hitnum=0

 Author:
          Eric Clayberg
          <[email protected]>

 Patrick Logan <[email protected]>
 wrote in message
 news:[email protected]...
 >
 > I wish the original Oak team had chosen to adopt Smalltalk
 > rather than invent Java

They tried to, but ParcPlace wanted too much on a per-copy royalty basis...sigh
 

4. Bah!  Real programmers reinvent the wheel all the time, it puts hair on your chest!  ...sigh, I've run into that far too many times over the years.  More often than not, the wheels that are reinvented tend to be rather square.  Too bad that schools often encourage this mentality during formal training.  [End soapbox]
5. This is some loose terminology that shifts depending on who you're speaking with.  For my purposes, an Object based (OB) language is a non-OO language that has been evolved towards Object-orientedness.  (C++, OO-COBAL, etc).  Some people call these bastardized OO languages.
6. Some productivity numbers from Software Productivity Research. (A sample of ave. source statements/function point: Smalltalk: 21, C: 128, C++: 53, Visual Basic 5: 29)
7. GoodStart - who's using Smalltalk - http://www.goodstart.com/whoswho.html

Copyright © 2000, Jason Steffler
Published in Issue 51 of Linux Gazette, March 2000