Re: more than one prefix argument

[Tim Cross <theophilusx@gmail.com>]

On Wed, Jul 27, 2011 at 4:25 PM, Andreas Röhler
<andreas.roehler@online.de> wrote:
> Am 26.07.2011 22:36, schrieb Drew Adams:
>>>>
>>>> what about allowing more than one prefix argument
>>>> by making interactive codes "p" and "P" sending
>>>> truly separated.
>>>
>>> We already have more than one kind of prefix argument: see
>>> universal-coding-system-argument for an example.  You can
>>> already define as many kinds of "prefix argument" as you'd
>>> like: just define a global flag and a command to set that
>>> flag, and have post-command-hook clear the flag unless (eq
>>> this-command 'my-prefix-setting-function).
>>
>> I don't think that's what Andreas is asking about.  He's not asking about
>> being
>> able to define alternative "prefix arg"-like things (to be used
>> separately).  I
>> think he wants the same user input to somehow distinguish two different
>> things
>> (?).
>>
>> At least that's my understanding.  IMO, he is simply confused,
>
> Hi Drew,
>
> maybe you are right. Then we must wait. I'll try to sum up the matter for
> the moment:
>
> current use of "p" and "P" might be enhanced. There is an intermix between
> both, doing nearly, but not precisely, the same.
>
> "P" quite often is used for completely different things than sending a
> number.
>
> (if (eq 4 (prefix-numeric-value))
>
> is used as a branch command. That's the interesting about it indeed.
>
> However, that's not clean. It's bad to read, because the fact of "4" has no
> meaning by themselves here. That's obscure programming style.
>
> In general let me stress: I'm living very well with Emacs as it is. Just
> saying: we can live still better.
>
> Cheers and thanks,
>
> Andreas
>

While P and p are similar, I'm not sure they are as similar as you
imply. Consider a very simple example. You have a function and you
want it to use a prefix arg and you want the raw form because you want
to distinguish between no prefix arg and C-u 1 or M-1. You then define
a second function, but this time, you want it to default to 1 if no
prefix arg or whatever the value is if one is provided, then the 'p'
numeric version is what you want. In each case, the P and p support
what you need without you having to do additional code. Yes, you could
solve this with just the P version, but then you would have to do more
code to handle the common case of just wanting to process the prefix
arg as a number.

This additional code would likely make the reading of the source even
more difficult than your example issue with the use of '4' in your
example. I would also suggest that if you don't like the literal 4 as
it doesn't make it clear what is going on (why 4?) you could define a
variable, such as