The version of ASDF in SBCL is a little out of date:
* (asdf:asdf-version) "3.3.1"
The ASDF home page contains the latest version: download "asdf.lisp" from the "Getting It" section.
I placed "asdf.lisp" under "~/common-lisp/", and then compiled the file (the compiled version is noticeably quicker to load):
* (compile-file "~/common-lisp/asdf.lisp")
This leaves a file "asdf.fasl" in "~/common-lisp/".
Add something like the following to "~/.sbclrc":
(let ((asdf-file (merge-pathnames "common-lisp/asdf.fasl"
(user-homedir-pathname))))
(when (probe-file asdf-file)
(load asdf-file)))
Then ASDF will be updated:
* (asdf:asdf-version) "3.3.7"