Re: Rationale behind conversion of a nil prefix arg to numeric 1

["Andreas Röhler" <andreas.roehler@easy-emacs.de>]

On 06.09.2016 16:20, Kaushal Modi wrote:
> On Tue, Sep 6, 2016, 7:22 AM Andreas Röhler 
> <andreas.roehler@easy-emacs.de <mailto:andreas.roehler@easy-emacs.de>> 
> wrote:
>
>     But let's go back to the simplest case of lower p in interactive spec:
>
>     What is easier to read/grasp
>
>     (setq counter (or arg 1)
>
>     or
>
>     (setq  counter (prefix-numeric-value arg))
>
>     IOW: in favor of avoiding these complex, tricky things. Let's have the
>     code as explicit as possible.
>
>
> Those 2 forms are not 100℅ equivalent. The equivalence goes only as 
> far as setting the default value of counter.
>
> If the user used (interactive "p"), counter need to be set to 4 
> regardless of whether the user used "C-4" as prefix or "C-u". In the 
> former case, arg would be "4", but in the latter case, it would be 
> "(4)", I.e. a list, not a number.

Not sure IIUC

(defun whatarg-p (arg)
   (interactive "p")
   (message "%s" arg))

Called with simply C-u without numeric argument gives me "4"

(4) would be the result with uppercase P

> Your simpler representation would not take care of the C-u case. If 
> the counter variable is used where a numeric arg is strictly required, 
> you will get an error. Here, prefix-numeric-value returns "4" when arg 
> is "(4)".
>
> -- 
>
> Kaushal Modi
>