Re: 7 logical-xor implementations in source tree

[Marcin Borkowski]

On 2019-07-28, at 10:04, Alan Mackenzie <address@hidden> wrote:

> Hello, Philippe.
>
> On Sun, Jul 28, 2019 at 09:09:01 +0200, Philippe Schnoebelen wrote:
>> On 2019/07/25 14:07, Mattias Engdegård wrote:
>> > 25 juli 2019 kl. 01.44 skrev Basil L. Contovounesios <address@hidden>:
>
>
>> > bool-equal, bool-equiv, bool=, bool-eq are all fine as far as I'm 
>> > concerned. `xnor' and `nxor', not so much.
>> > Racket has `boolean=?', but presumably it only copes with #t/#f.
>> > I'll be using `equiv' as placeholder below for brevity.
>
>> I like the name `iff' for this function.
>
> No, please don't use the name `iff' here.  In mathematical circles, iff
> means "if and only if", and has done for many decades/several centuries.
> Introducing it into Emacs with a radically different meaning will be
> jarring in the extreme to anybody with a maths background.

Out of curiosity: how is that a "radically different meaning"?  I assume
that we are talking about a function `iff' such that
(iff nil nil) evaluates to t
(iff nil <non-nil>) evaluates to nil
(iff <non-nil> nil) evaluates to nil
(iff <non-nil> <non-nil>) evaluates to t (or perhaps the latter
<non-nil>)

This could of course be generalized to n arguments, though I'm not sure
whether anyone would want that (as with xor, there is more than one
"natural" way to do that).

If so, this is precisely the meaning we are talking about, no?

Also, Wikipedia claims that "iff" is relatively new (the fifties), btw.

Best,

--
Marcin Borkowski
http://mbork.pl