Lisp isn't one language like Ruby or PHP; it is a family. Some members of that family are fully self hosting. E.g. to build SBCL, you need an implementation of

Lisp isn't one language like Ruby or PHP; it is a family. Some members of that family are fully self hosting. E.g. to build SBCL, you need an implementation of Common Lisp. It doesn't have to be SBCL.