I'd also like to point out that Guile can be bootstrapped with a Scheme interpreter (not just Guile), or it can be built with the interpreter in Guile itself, w

I'd also like to point out that Guile can be bootstrapped with a Scheme interpreter (not just Guile), or it can be built with the interpreter in Guile itself, which is written in C. So there are a few choices here that increase the number of bootstrap paths through which one can arrive at Guile. I'd say that this is a desirable property as it allows for an elegant reduction of the bootstrap problem; conversely a program requiring a version of itself to be built has a much more complicated bootstrap story that either involves trust in large binaries or recursion into the early days of the compiler's first implementations. (GHC matches the latter story, unfortunately.)