Bootstrapping Common Lisp using Common Lisp

Some Common Lisp implementations evolve through careful modifications to an existing image. Most of the remaining implementations are bootstrapped using some lower-level language, typically C. As far as we know, only SBCL is bootstrapped from source code written mainly in Common Lisp. But in most cases, there is no profound reason for using a language other than Common Lisp for creating a Common Lisp system, though there are some annoying details that have to be dealt with. We describe the bootstrapping technique used with SICL, a modern implementation of Common Lisp. Though both SICL and the bootstrapping procedure for creating it are still being worked on, they are sufficiently evolved that the big picture outlined in this paper will remain valid. Our technique uses first-class global environments to isolate the host environment from the environments required during the bootstrapping procedure. Contrary to SBCL, and implementations written in some other language, in SICL, we build the CLOS MOP classes and generic functions first. This technique allows us to use the CLOS machinery for many other parts of the system, thereby decreasing the amount of special-purpose code, and improving maintainability of the system