Why 3 different evaluators?

[rixed]

According to the doc, guile currently maintain 3 evaluators:

- the new VM
- an evaluator written in scheme
- the old C evaluator, used for bootstrapping the compiler.

That's a lot of code just to bootstrap the compiler.  Why not bootstrapping the
compiler from either previous installed guile or (as fall-back) some provided
.go bytecode instead? Wouldn't that make guile code significantly simpler to
maintain and faster to compile?