That's great but it isn't the same thing as what I linked to, which is a small program loaded by the Raspberry Pi's boot loader.

What I'm after is the Common Lisp or Scheme equivalent to something like the FreeBSD kernel's libkern, plus a compiler/linker capable of generating an image that could be read into memory by a boot loader:

https://github.com/freebsd/freebsd/tree/master/sys/libkern