I just managed to implement the first version of Visual Stepper in the GRASP development environment that I've been working on for some time.
While GRASP is far from being production-ready, and there's still a lot of work to be done (it currently only handles the lambda-calculus and no macros whatsoever), I think that it might already have some value.
Anyway, here's a link to a video showing the visual stepper at work:
https://www.youtube.com/watch?v=wN8Fy5xTXeQ
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