If you want to play with reading/recreating a very small Tcl interpreter, recently I put Picol (a 500 lines of C code Tcl interpreter) on Github. It was still on the web, but a bit more "hidden". I had a chance to re-read the code, and it is not in the category of code I regret writing :D Still relatively useful for newcomers, I hope.
Thanks for that effort. Some time ago, I got Picol working on an Arduino-compatible microcontroller board with minimal effort. I was working towards making my own programmable calculator, and test-drove a number of simple interpreters, including yours and a couple others.
Project languished due to my attention span running out, but I still have my adaptations of those codes on my drive, in case I ever pick it up again.
Thanks for Picol! I saw it as a young engineer, and found the simplicity inspiring. It inspired me to write Tcl interpreters as starter projects in the next languages I was picking up, and I learned a lot by trying to push performance , functionality, and correctness.
Your little project ended up inspiring cumulative months of joyful hacking.
https://github.com/antirez/picol