Comment 1 for bug 375326

There are more problems with SB-WALK: It macroexpands and uses declarations
introduced by such macro expansion. It also does not properly update the lexenv
that passed to the function with which WALK is invoked (I forgot the details, and
I do not have the code at hand right now.)

IMHO, SB-WALK could be rewritten; it's very old code, was once written with
portability in mind, then kludged to be SBCL specific again.