Smalltalk and Object Orientation: an Introduction - Free

These concepts of messages, receivers, objects etc. will be explained in a later chapter. Hopefully,
by the end of this book you will read the above definition and say “of course”.
5.7 Working with Smalltalk
5.7.1 Open a VisualWorks image
First of all start up your current VisualWorks image, for example, on a UNIX system you might enter:
visualworks Visual.im
If this is not local you may need to specify a path name for the object engine or the image. For example,
if you are on a UNIX system:
/usr/local/ visual/bin/visualworks
/usr/jjh/visual.im
If you are using a Macintosh or a Windows -95 PC then you just double click on the image file and the
VisualWorks virtual machine will be used to open it.
Once you have started VisualWorks, save the image to your own file store and exit. To do this, first
select the save as option off the file menu on the VisualLauncher. You will be requested to provide a
name for your image. Note that if you do not give a path name as well as the image name, the image file
will be saved in the current directory.
Once you have created the image file, you can exit from VisualWorks. To do this you select the Exit
option (again from the File menu on the VisualLauncher).
5.7.2 Selecting, compiling and executing Smalltalk
If you have not already done so, type the following into the Workspace:
Transcript show: 'Hello World'.
Transcript cr.
Transcript show: (3 + 4) printString.
Transcript cr.
Select the text and do it. That is, select the text with the left mouse button, then bring u p the right
(or middle on a three button mouse) mouse menu and select the do it option. You should then see the
phrase “Hello World” and the number 7 appear in the Transcript window.
5.7.3 Using some VisualWorks tools
In many books you are presented with some so urce code to type in and execute, but are given very little
guidance on how to deal with errors etc. Therefore in this section, you get to type in some (intentionally
buggy) Smalltalk code and to compile it. This forces you to use tools such as the debugge r to identify
and correct the errors. After all, at this stage, it is likely that you will write buggy Smalltalk rather than
perfect Smalltalk.
Type in the following exactly as it is (there are errors included so that you get some practice using
the tools available in Smalltalk).
| temp |
temp := Set New.
temp add: 'John'.
temp add: 'Paul'.
temp add: Peter.
temp do: [:item | Transcript show item].
temp inspect.
Now select all the code and “do it” as before. You should now get a dialog box such as that
illustrated below:
57