step-by-step 
Author Message
 step-by-step

Does anyone know of a Smalltalk interpreter, whereby you can step through
a method, and sequence of method calls, making change of variable values
completely transparent? I am especially interested in using such a device
for teaching novice's how to use Smalltalk.


Mon, 28 Jul 1997 19:36:38 GMT  
 step-by-step

Quote:

>Does anyone know of a smalltalk interpreter, whereby you can step through
>a method, and sequence of method calls, making change of variable values
>completely transparent? I am especially interested in using such a device
>for teaching novice's how to use Smalltalk.

   Most Smalltalk evironment comes with a de{*filter*} which is available
in the development environment.  All changes (including source code) in
the de{*filter*} are dynamic and real - just be careful of what you change
can affect the whole system and may even hang your system.

   The simplest way of bringing up a de{*filter*} to trace your program
execution is to precede the statement(s) you are evaluating with:

    self halt.

or, you if you know which method in your class you want to debug you
can insert a #halt message there.  All objects in Smalltalk should
understand #halt - at least in the development environment.

   I said "you if you know which method in your class you want to
debug" because normally you don't want to put a halt in the system
classes - that can be a Russian-Roullette approach to practice your
three-finger salute (Ctrl-Alt-Del) or even start the Hunt for Red
October...  Uh, Red Button.

   Within IBM Smalltalk and IBM VisualAge de{*filter*}, there are four
buttons: Into, Over, Return, Resume.

   The "Into" button will try to execute the next smallest unit of
work.  If the current statement invokes other Smalltalk messages,
the system will try to locate the source code for that method,
add a frame to the processing stack and take you into that method.
If the current statement invokes a primitive, it will execute that
primitive and take you to the next statememt.

   The "Over" button will execute the current statement and move
to the next statement.

   The "Return" button will execute all statements in the current
method to return from the current method.

   The "Resume" button will resume normal processing to cancel
out the last halt - when you don't want to trace/debug any more
and to finish up the process execution.

Jimmy Nguyen - VisualAge Development Team



Fri, 01 Aug 1997 23:50:10 GMT  
 
 [ 2 post ] 

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