This is a demo that I (Mike Gleicher) made originally to show in class. Haochen Shi helped add features and make the program more usable.
While you can look at the program source code (for example using "view source"), we don't recommend that you try to read the code. Use the program to understand the little "mini programs" - the actual program itself is an interpreter for these mini programs.
You can put things into "reverse" mode and watch the program run "backwards" (to help see how things work when you think about it as local to gloabal). Note that programs with save/restore do not run backwards.
TransformToy is the demo program with a few examples.