debuggers for teaching

[ucdavis.ucdavis.edu!windley@ucdavis.ucdavis.edu (Phil Windley)]

Has anyone written a program that demonstrates scheme evaluation in both
the substitution and environment model of evaluation (Sussman and Abelson)?
I've been contemplating such a "debugging" environment for my class.  The
substitution model could be text based, but I think that the environment
model would have to be based on X or some other windowing system.  I think
a tool like this would be great for teaching students about program
evaluation. 

--
Phil Windley                          |  windley@iris.ucdavis.edu
Division of Computer Science          |  ucbvax!ucdavis!iris!windley
College of Engineering                |  (916) 752-7324 (or 3168)
University of California, Davis       |  Davis, CA 95616