isbn9789526046266

Figure 11.4: The PyDev debugger for Python programs within the Eclipse IDE (image from Helminen,
2009). A Python program is being executed, with line 4 up next. Threads and call stacks
are listed in the top left-hand corner. Global and local variables are shown on the right.
The yellow highlight signifies a change in the value of a variable.
programs may be large in terms of both code and data. For such reasons, the visualization shown by
a typical visual debugger is not particularly graphic, and consists primarily of text within standard GUI
widgets.
Bennedsen and Schulte (2010) conducted an experimental study in which a group of CS1 students
used the visual debugger built into the BlueJ IDE to step through object-oriented programs, while a
control group used manual tracing strategies. They found no significant differences in the performance of
the groups on a post-test of multiple-choice questions on program state. A rerun of the experiment using
a different debugger yielded similar results. Bennedsen and Schulte surmise that “it could be that the
debugger is not useful for understanding the object interaction but just for finding errors in the program
execution” (p. 18).
Despite their limitations, visual debuggers are worth a mention in this section because they are highly
useful tools that novices do encounter in CS1 courses, because they do visualize certain aspects of program
dynamics, and because they serve as a point of departure for reviewing the more education-oriented systems
below.
11.3.2 Many educational systems seek to improve on regular debuggers
Most of the systems reviewed in this chapter are program animation tools that can be thought of as
educators’ attempts to improve on regular visual debuggers. Some of these systems look very similar to
regular visual debuggers, others feature more unusual visualizations.
An early system on the Atari: Basic Programming
An early educational PV system that supported visual tracking of program execution was Basic
Programming, “an instructional tool designed to teach you the fundamental steps of computer
programming” (Robinett, 1979). Shown in Figure 11.5, Basic Programming was an integrated environment
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