Re: pcase and minus-sign

[Andreas Röhler]

On 30.11.2016 13:38, Joost Kremers wrote:
> On Wed, Nov 30 2016, Andreas Röhler wrote:
> > Hi,
> >
> > see code below. With numerical argument "1", first pattern is matched 
> > as expected.
> >
> > However without arg the minus is matched - the second pattern, not 
> > the default "_" at last.
> >
> > Any explanation?
> >
> > (defun foo (arg)
> >    (interactive "P")
> >    (pcase arg
> >      (1 (message "%s" "ARG was `1'"))
> >      (- (message "%s" "ARG was minus-sign"))
> >      (_ (message "%s" "ARG not minus-sign"))))
>
> Probably because - is a symbol and hence a variable. It works if you 
> quote it:
>
> (defun foo (arg)
>  (interactive "P")
>  (pcase arg
>    (1 (message "%s" "ARG was `1'"))
>    ('- (message "%s" "ARG was minus-sign"))
>    (_ (message "%s" "ARG not minus-sign"))))

Thanks, that helps. Seems it relates to the following in docstring:

SYMBOL    matches anything and binds it to SYMBOL.

Now if I use some arbitrary char, like "a",

(defun foo (arg)
  (interactive "P")
  (pcase arg
    (a (message "%s" "ARG was `a'"))
    (1 (message "%s" "ARG was `1'"))
    ('- (message "%s" "ARG was minus-sign"))
    (_ (message "%s" "ARG not minus-sign"))))

It picks that a-branch at any case - as documented but strange.