Overriding cl package symbols

[Andy Peterson]

parenscript does not redefine "defun", it imports cl:defun and exports it
again.

CL-USER> (eq 'ps:defun 'cl:defun )
T

Exporting has nothing to do with the package lock.  it refers to when you
try to redefine cl:defun.

You can define your own defun in your own package. The library *Series *does
this but it does not export it.

from s-package.lisp

(defpackage #:series
    (:use #:cl)
  (:export
   ...
    )

  (:shadow
   #:let #:let* #:multiple-value-bind #:funcall #:defun
   #+(or cmu scl) #:collect #+(or cmu scl) #:iterate)
   ....
)

from s-code.lisp:

;; EXTENSION
(defmacro defun (name lambda-list &environment *env* &body body)
  (if (dolist (form body)
        (cond ((and (stringp form) (eq form (car body))))
              ((and (consp form) (eq-car form 'declare))
               (if (assoc 'optimizable-series-function (cdr form)) (return
t)))
              (t (return nil))))
      (define-optimizable-series-fn name lambda-list body)
    (progn (undefine-optimizable-series-fn name)
           `(cl:defun ,name ,lambda-list
              . ,body))))

you could export it, put it would generate conflicts when you use it.

SERIES> (export 'defun)
T
SERIES> (in-package :cl-user)
#<PACKAGE "COMMON-LISP-USER">
CL-USER> (use-package :series)
USE-PACKAGE #<PACKAGE "SERIES"> causes name-conflicts in
#<PACKAGE "COMMON-LISP-USER"> between the following symbols:
  SERIES:DEFUN, COMMON-LISP:DEFUN
   [Condition of type NAME-CONFLICT]
See also:
  Common Lisp Hyperspec, 11.1.1.2.5 [:section]
; Evaluation aborted on #<NAME-CONFLICT {1002576393}>.
CL-USER>

I hope this clarifies it for you.

andy peterson


On Sun, 9 Jun 2019 at 15:39, James Gunn <jgunn987 at gmail.com> wrote:

> Hello,
>
> I have been reading the source code for parenscript and I am keen to find
> out how you override locked symbols? In the parenscript package there are
> exports such as "#:defun". I have tried myself to create my own package
> that exports defun but i get the following error message(using SBCL)
>
> "Lock on package COMMON-LISP violated when proclaiming DEFUN as a function"
>
> I'd be very interested in finding out how you got around this.
>
> Thank you,
>
> James Gunn
>
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