Common Lisp Problems - Can't write a code walker

[Guy Steele <gls@THINK-AQUINAS.ARPA>]

    Date: 1 Apr 86 13:27 PST
    From: Gregor.pa@Xerox.COM

    This is the first of a few messages describing the problems I have had
    with Common Lisp while writing Portable Common Loops....

    ...

    3- Implementations have special forms in their extended lisps that are
    not Common Lisp special forms.  I don't know if there is anything we can
    do about this, but I thought I would mention it.  (I suppose we could
    agree on a common syntax for defining code walker templates and a common
    mechanism for retrieving them but that doesn't seem too likely).

Such implementations are in violation of the Common Lisp specification.
Page 57 of CLtL is very clear about this.  An implementation of Common
Lisp is NOT free simply to randomly add a new special form as an
"extension"; it must also provide an equivalent macro definition so that
MACROEXPAND may be used to get rid of it for purposes of program
analysis.