Re: [Gcl-devel] Re: a little more info

[Pascal Bourguignon]

Camm Maguire writes:
> Greetings, and thanks for this!
> 
> I think if you delete the home package of a symbol, there is nothing
> you can do, even with imports or exports.

You cannot find the symbols, but if you have a reference on them, you
can still import them!
 
> >(symbol-package 'define-symbol-macro)
> 
> #<"COMMON-LISP-USER" package>
> 
> >(delete-package 'common-lisp-user)
> 
> T
> 
> NIL>(symbol-package 'define-symbol-macro)
> 
> #<NIL package>
> 
> ... but I am clueless about packages, so this could be quite wrong.


Well, I would have expected the later to fail because there's no
package where to read the form, but we're in implementation specific
behavior.  clisp just falls back to COMMON-LISP.

[1]> (symbol-package 'define-symbol-macro)
#<PACKAGE COMMON-LISP>
[2]> (delete-package *package*)

** - Continuable Error
The value of *PACKAGE* was not a package and was reset. The old value was
      #<DELETED PACKAGE COMMON-LISP-USER>
     . The new value is #<PACKAGE COMMON-LISP>.
If you continue (by typing 'continue'): Proceed with the new value.
The following restarts are also available:
ABORT          :R1      ABORT
Break 1 CL[3]> :a
CL[4]> 


Clearly gcl uses the trick of having a NIL package, that still uses
COMMON-LISP and in which the second DEFINE-SYMBOL-MACRO is interned.


In gcl:

>(let ((sym (intern "NEW-SYMBOL-FROM-HERE" *package*)))
       (delete-package *package*)
       (setf *package* (make-package "MY-OWN-NEW-PACKAGE" :use 
'("COMMON-LISP")))
       (print `(home package of ,sym = ,(symbol-package sym)))
       (import sym *package*)
       (print `(home package of ,sym = ,(symbol-package sym)))
       (find-symbol  "NEW-SYMBOL-FROM-HERE" *package*))

(NIL::HOME PACKAGE NIL::OF NIL::NEW-SYMBOL-FROM-HERE = #<NIL package>) 
(NIL::HOME PACKAGE NIL::OF NEW-SYMBOL-FROM-HERE = #<NIL package>) 
NEW-SYMBOL-FROM-HERE
:INTERNAL

MY-OWN-NEW-PACKAGE>


In clisp:

[1]> (let ((sym (intern "NEW-SYMBOL-FROM-HERE" *package*)))
       (delete-package *package*)
       (setf *package* (make-package "MY-OWN-NEW-PACKAGE" :use 
'("COMMON-LISP")))
       (print `(home package of ,sym = ,(symbol-package sym)))
       (import sym *package*)
       (print `(home package of ,sym = ,(symbol-package sym)))
       (find-symbol  "NEW-SYMBOL-FROM-HERE" *package*))

(#:HOME PACKAGE #:OF #:NEW-SYMBOL-FROM-HERE = NIL) 
(#:HOME PACKAGE #:OF NEW-SYMBOL-FROM-HERE = #<PACKAGE MY-OWN-NEW-PACKAGE>) 
NEW-SYMBOL-FROM-HERE ;
:INTERNAL
MY-OWN-NEW-PACKAGE[2]> 

(clisp gives the homeless symbols a new home when imported...)

-- 
__Pascal Bourguignon__                     http://www.informatimago.com/

"Our users will know fear and cower before our software! Ship it!
Ship it and let them flee like the dogs they are!"