On 1 Aug 2017, at 17:21, Pascal Bourguignon <pjb@informatimago.com> wrote:

It works perfectly, but on clisp, since DYNAMICALLY-MODIFIABLE doesn’t come from EXT.  
Where does it come from???

Oh, and but on abcl, which also has a EXT package.  

I would advise remaining those short-named packages, unless they implement a CDR-specified API.
“ORG.CLISP.EXT” sounds a good unique name, or at least “CLISP-EXT”… 

[pjb@despina :0.0 ~]$ clall '(compile-file "/tmp/d.lisp")'

Armed Bear Common Lisp:
Implementation: Armed Bear Common Lisp 1.4.0
    on Mac OS X 10.12.6
    on X86_64 NIL (despina.home)

Reading of: "(compile-file \"/tmp/d.lisp\")"
signaled no error

Evaluation of: (COMPILE-FILE "/tmp/d.lisp")
signaled the following error:
  #<READER-ERROR {2D87B142}>
  The symbol "DYNAMICALLY-MODIFIABLE" was not found in package EXT.
wrote nothing on *ERROR-OUTPUT*
wrote nothing on *TRACE-OUTPUT*
wrote the following *STANDARD-OUTPUT* (lines excluded):
; Compiling /private/tmp/d.lisp ...
returned no value

__Pascal J. Bourguignon__