I have a fairly complete freeware implementation of the "R5" version of the Scheme programming language, that runs on the Raspberry Pi 400 and quite likely on other 64-bit versions of the Pi. The spinoff project is called "Weasel Scheme", and it runs in a terminal shell. If anyone is interested in trying it out, or otherwise playing with it, get in touch with me.

Weasel Scheme presently has at least limited access to the Pi's GPIO pins -- it can use them to read and write logic levels. More capability is likely in the future, and you can also use non-Weasel-Scheme stuff to set up the GPIO pins however you like, so that Weasel Scheme can then read and write them.

This project is a spinoff from a much larger Scheme project for MacOS that I have been supporting for years; namely, "Wraith Scheme" (google it, possibly with my name -- Jay Freeman -- also in the search window), which requires MacOS and Xcode to build. Thus I can't post buildable Linux source in, e..g., a GitHub repository. Notwithstanding, I can get you a compiled executable and probably more source code than anyone but me would care to look at, and also plenty of documentation. If enough people are interested, I will put things together in a more easily accessible form.

Weasel Scheme is still in development, and thus is not listed in the Scheme folks' master list of Scheme implementations, nor should it be (yet).