Re: 7 logical-xor implementations in source tree

[Marcin Borkowski]

On 2019-07-30, at 11:36, Alan Mackenzie <address@hidden> wrote:

> Hello, Marcin.
>
> On Sun, Jul 28, 2019 at 21:43:19 +0200, Marcin Borkowski wrote:
>
>> 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>)
>
> Er, it's not radically different.  My brain seems to have been switched
> off when I wrote my last post.  Apologies.

No worry.

> Less importantly, I don't like iff being used in this way.  I'm not sure
> why.  Maybe it's because I've been used to iff applying solely to TRUE
> and FALSE.  Maybe it's that I've been used to iff declaring a
> proposition, rather than being something to be calculated.

Well, these are subjective points, but there are much stronger arguments
against `iff' raised by others...

Best,

-- 
Marcin Borkowski
http://mbork.pl