Re: Unary /

[Paul Eggert]

On 10/15/2015 11:45 AM, Stefan Monnier wrote:
> Indeed, the - has the same asymmetry, but it seems that "unary -" is  much
> more commonly found operator than "unary /".

I suspect David was being ironic....

Unary / is rare in Elisp code, partly because the GNU Emacs byte 
compiler complains about it, partly because it doesn't work in GNU Emacs 
24.2 and earlier, partly because it has the Common Lisp semantics in 
XEmacs, and partly because one doesn't often need the reciprocal of a 
floating-point number. With all that being said, it's a bit more useful 
for (/ N) to return the reciprocal of N than to return N, so we might as 
well be compatible with CL here.

I've proposed a patch to change unary / to behave more like CL, in 
Bug#21690. Since we're in feature-freeze now isn't a good time to be 
changing the semantics of /, but there's no rush. In the meantime we can 
leave the byte-compiler alone, as its bogus warning about (/ N) will 
help scare users away from the soon-to-be-withdrawn semantics.