Any reason slime-asdf doesn't (require :asdf)? I think asdf already provides :asdf so it shouldn't break anything worse if loaded on a system where (require :asdf) can't possibly work, but it'd make (slime-setup '(slime-asdf)) work obviously on systems where :asdf isn't available by default, but (require :asdf) *does* work (e.g. ECL)