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

[Charles Millar <millarc@verizon.net>]

On 09/06/2016 10:20 AM, Kaushal Modi wrote:
> On Tue, Sep 6, 2016, 7:22 AM Andreas Röhler <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. 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)".
>
>> --
>
I have read this thread as well as the other suggested readings. If the 
purpose of either p or P is to pass arguments, I do not understand the 
rationale of allowing C-u when using the interactive upper case P. As 
noted above, It returns an integer as the only element in a list, which 
if evaluated returns an error. Is there a use for this? Such as you may 
want an error?

Charlie Millar