Re: 7 logical-xor implementations in source tree

[Basil L. Contovounesios]

Drew Adams <address@hidden> writes:

> I don't understand what all the excitement
> about defining an `xor' (with whatever name)
> operator is about.
>
> Common Lisp, like Emacs Lisp, has a bit-wise
> xor operator.  That makes sense - useful.
>
> And Common Lisp, like Emacs Lisp, does _not_
> have an xor operator for arbitrary Lisp values.
>
> https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node75.html
>
> Why is it important that Emacs Lisp have such
> an operator?  (Answer: it's not - YAGNI.)

If YAGNI, why are there currently 7 copies of this function in the Emacs
sources?

No-one said it's vitally important; it's just a minor nice-to-have.

> Is it hard to understand (eq (not a) (not b))?
> Is evaluation of that inefficient?  Is it too
> verbose?
>
> What's the motivation for all of this?

Same reason proper-list-p was added: reducing existing code duplication
and providing yet another convenience function for those that like it.

> My vote's against adding any such operator.

-- 
Basil