For this sample we include a work in progress ... a new version of the Pascal program animator that was the primary result of the predecessor DynaLab project. The DynaLab Pascal program animator is a very nice and comprehensive system for animating Pascal programs under full user control, constructed largely by WebLab team members Frances Goosey and Chris Boroni under the supervision of project director Rocky Ross. Features of the animator that are especially useful for teaching and learning include:

Stepwise Execution: Programs are displayed in a window that allows for various stepping modes of execution as program statements are highlighted and changing variable values are displayed. Although the animation environment looks similar to a good debugger, it has been designed for teaching and learning rather than debugging, which makes it much different than a debugger.

Reverse Execution: A user can reverse execution arbitrarily far to successively execute a set of puzzling statements numerous times;

Time and Space Complexity Analysis: A pane in the animation window keeps track of the "cost" of executing a program; a variable pane also displays the contents of program variables. The two can be used for time and space complexity analysis and study.

A Library of Programs: A library of programs constructed by an expert comes with the animator, so that students can study well-crafted programs. This library can be extended easily by an instructor.

An Editor: A built-in text editor allows instructors and students alike to enter programs for compilation and execution; programs from the library can be modified as well.

A Virtual Machine: The animator includes a virtual computer called the Education Machine, or just E-machine. The E-machine is capable of running E-machine code both in the normal (forwards) direction or in reverse, which allows source programs to be animated in reverse.

A Compiler: A Pascal compiler, which translates Pascal programs into E-code is included in the package, completing the system.

The entire DynaLab package runs on PCs running Microsoft Windows 95 and NT. It also runs under Windows 3.1 with the Win32s extension. It can be downloaded and used by visiting the DynaLab Web site.

The sample given with this page gives a preview of the port of the DynaLab program animator to the Web.

NOTE:

It is important to keep in mind that the sample given here is a work in progress and still lacks many of the features available with the DynaLab program animator. These features are currently under development and will be available in the future.

Although this sample works very well, it is written in Java (using Java 1.1 features), so your browser must be Java ready and support Java 1.1. Currently, the program animator runs best using Netscape 4.0.5 with the Java 1.1 enhancements. The ongoing changes with the Java language, Java JDKs and Java Virtual Machine implementations on the various browsers sometimes causes inconsistencies in the operation of the Program Animation applet. It should also be noted that there is a significant delay as the applet initially loads and when a program is first selected for animation (via the File menu), but once the animation starts, it should proceed smoothly.

We welcome any feedback!