Re: Overloading of primitive operators

[kanderso@DINO.BBN.COM]

  But if I do this, for any package to use my package's definition of +, it too
  must shadow the +.  Such a package better shadow such symbols before using
  the LISP package, and heavens forbid if some package other than mine also
  pulls the same trick on the operator +...

At least i the LISP i'm using, this works fine:

;;; Make a package the way you like it:
(make-package 'nat-lisp :use '(pcl lisp))
(shadow '(lisp:+ lisp:-) 'nat-lisp)
(export '(nat:+ nat:-) 'nat-lisp)
;;; Define the functions you want ...

;;; Define a package for users to use:
(make-package 'nat-lisp-user :use '(nat-lisp pcl lisp))
(in-package 'nat-lisp-user)
... now users can use your generic lisp ...

  The idea of using shadowed symbols is not a real solution since one has
  really introduced a new symbol (i.e., the symbols have the same name, but
  are two different symbols).  In C++, the user of an overloaded primitive
  operator does not need to do anything special.
  
Perhaps, but you get what you want for about 5 lines of software.  Not
only do you get the behavior you want in nat:+, but you also get the
implementor's lisp:+ to build it in terms of.  This gives you
something to use while you write a truely object oriented LISP from
scratch, and get X3J13 to accept it as a standard.

BTW, C++ does place restrictions on operators that can be overloaded
[at least in 1984].  For example, you can't change the syntax of an
operator, and you can't add new ones like "**" for exponentiation.
These issues don't even come up in LISP.  To be fare, perhaps you
should start a discussion about this on some C++ group.

k