How to detect C-u supplied arguments from other prefix arguments

How to detect C-u supplied arguments from other prefix arguments

[Dieter Wilhelm]

Hi

I'd like to detect whether prefix arguments of a command are supplied
by C-u or otherwise.

My idea is to use this-command-keys and compare it to some string,
like the following pseudo code:

(defun bla (arg)
  (interactive "p")
  (when (string= "C-u" (substring (this-command-keys) 0 2))
    (message "hurray")))

I just don't understand how to compare key sequences.  Or maybe
there's better way of doing it?

-- 
    Best wishes

    H. Dieter Wilhelm
    Darmstadt, Germany

Re: How to detect C-u supplied arguments from other prefix arguments

[Kevin Rodgers]

Dieter Wilhelm wrote:
> Hi
> 
> I'd like to detect whether prefix arguments of a command are supplied
> by C-u or otherwise.
> 
> My idea is to use this-command-keys and compare it to some string,
> like the following pseudo code:
> 
> (defun bla (arg)
>   (interactive "p")
>   (when (string= "C-u" (substring (this-command-keys) 0 2))
>     (message "hurray")))
> 
> I just don't understand how to compare key sequences.  Or maybe
> there's better way of doing it?

Yuck.  If all you're concerned about is whether the prefix arg was
specified by 1 or more C-u keys (with no minus sign or digits), you
can use (consp current-prefix-arg).

-- 
Kevin Rodgers
Denver, Colorado, USA

Re: How to detect C-u supplied arguments from other prefix arguments

[dieter.wilhelm]

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On 8 août, 07:06, Kevin Rodgers <kevin.d.rodg...@gmail.com> wrote:
> Dieter Wilhelm wrote:
> > I'd like to detect whether prefix arguments of a command are supplied
> > by C-u or otherwise.
> > My idea is to use this-command-keys and compare it to some string,
> > like the following pseudo code:
>
> > (defun bla (arg)
> >   (interactive "p")
> >   (when (string= "C-u" (substring (this-command-keys) 0 2))
> >     (message "hurray")))
>
> > I just don't understand how to compare key sequences.  Or maybe
> > there's better way of doing it?
>
> Yuck.  If all you're concerned about is whether the prefix arg was
> specified by 1 or more C-u keys (with no minus sign or digits), you
> can use (consp current-prefix-arg).

Unfortunately this doesn't work in all cases:  I'd also like to
specify numerical
arguments with C-u (not only powers of 4).   For example

C-u 3 M-x some-command

and would like to distinguish it from other means of supplying
numerical
arguments e.g.:

M-3 M-x some-command

> Kevin Rodgers
Thanks
  Dieter

Re: How to detect C-u supplied arguments from other prefix arguments

[Johan Bockgård]

Dieter Wilhelm <dieter@duenenhof-wilhelm.de> writes:

> I'd like to detect whether prefix arguments of a command are supplied
> by C-u or otherwise.
>
> My idea is to use this-command-keys and compare it to some string,
> like the following pseudo code:
>
> (defun bla (arg)
>   (interactive "p")
>   (when (string= "C-u" (substring (this-command-keys) 0 2))
>     (message "hurray")))
>
> I just don't understand how to compare key sequences.

You want to check for the character ^U, not the three-character string
`C - u'. Like

    (eq ?\C-u (aref (this-command-keys) 0))

(The whole idea seems a bit ugly though.)

`(substring ... 0 2)' returns a string of length 2, btw.

-- 
Johan Bockgård

Re: How to detect C-u supplied arguments from other prefix arguments

[dieter.wilhelm]

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On 8 août, 13:55, bojohan+n...@dd.chalmers.se (Johan Bockgård) wrote:
> Dieter Wilhelm <die...@duenenhof-wilhelm.de> writes:
> > I'd like to detect whether prefix arguments of a command are supplied
> > by C-u or otherwise.
>
> > My idea is to use this-command-keys and compare it to some string,
> > like the following pseudo code:
>
> > (defun bla (arg)
> >   (interactive "p")
> >   (when (string= "C-u" (substring (this-command-keys) 0 2))
> >     (message "hurray")))
>
> > I just don't understand how to compare key sequences.
>
> You want to check for the character ^U, not the three-character string
> `C - u'. Like
>
>     (eq ?\C-u (aref (this-command-keys) 0))

hurray it works, thanks a lot!
>
> (The whole idea seems a bit ugly though.)

Why?  In Emacs there are just too little short key combinations free.
I'd like to achieve
a switch for certain functions depending whether their arguments ARG
are supplied by C-u or not.

For example: M-d might kill ARG word with the following boundary/
whitespace or without,
or C-t might drag a character ARG chars away and in the other case
merely transpose neighbouring chars some ARG chars away.

Re: How to detect C-u supplied arguments from other prefix arguments

[Barry Margolin]

In article <1186576048.530383.47680@q75g2000hsh.googlegroups.com>,
 dieter.wilhelm@googlemail.com wrote:

> On 8 ao?t, 13:55, bojohan+n...@dd.chalmers.se (Johan Bockg?rd) wrote:
> > Dieter Wilhelm <die...@duenenhof-wilhelm.de> writes:
> > > I'd like to detect whether prefix arguments of a command are supplied
> > > by C-u or otherwise.
> >
> > > My idea is to use this-command-keys and compare it to some string,
> > > like the following pseudo code:
> >
> > > (defun bla (arg)
> > >   (interactive "p")
> > >   (when (string= "C-u" (substring (this-command-keys) 0 2))
> > >     (message "hurray")))
> >
> > > I just don't understand how to compare key sequences.
> >
> > You want to check for the character ^U, not the three-character string
> > `C - u'. Like
> >
> >     (eq ?\C-u (aref (this-command-keys) 0))
> 
> hurray it works, thanks a lot!
> >
> > (The whole idea seems a bit ugly though.)
> 
> Why?  In Emacs there are just too little short key combinations free.
> I'd like to achieve
> a switch for certain functions depending whether their arguments ARG
> are supplied by C-u or not.
> 
> For example: M-d might kill ARG word with the following boundary/
> whitespace or without,
> or C-t might drag a character ARG chars away and in the other case
> merely transpose neighbouring chars some ARG chars away.

And what if the user decides to bind a different keystroke to 
universal-argument?

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

Re: How to detect C-u supplied arguments from other prefix arguments

[Dieter Wilhelm]

Barry Margolin <barmar@alum.mit.edu> writes:

> In article <1186576048.530383.47680@q75g2000hsh.googlegroups.com>,
>  dieter.wilhelm@googlemail.com wrote:
>
>> On 8 ao?t, 13:55, bojohan+n...@dd.chalmers.se (Johan Bockg?rd) wrote:
>> > Dieter Wilhelm <die...@duenenhof-wilhelm.de> writes:
>> > > I'd like to detect whether prefix arguments of a command are supplied
>> > > by C-u or otherwise.
>> >
>> > > My idea is to use this-command-keys and compare it to some string,
>> > > like the following pseudo code:
>> >
>> > > (defun bla (arg)
>> > >   (interactive "p")
>> > >   (when (string= "C-u" (substring (this-command-keys) 0 2))
>> > >     (message "hurray")))
>> >
>> > > I just don't understand how to compare key sequences.
>> >
>> > You want to check for the character ^U, not the three-character string
>> > `C - u'. Like
>> >
>> >     (eq ?\C-u (aref (this-command-keys) 0))
>> 
>> hurray it works, thanks a lot!
>> >
>> > (The whole idea seems a bit ugly though.)
>> 
>> Why?  In Emacs there are just too little short key combinations free.
>> I'd like to achieve
>> a switch for certain functions depending whether their arguments ARG
>> are supplied by C-u or not.
>> 
>> For example: M-d might kill ARG word with the following boundary/
>> whitespace or without,
>> or C-t might drag a character ARG chars away and in the other case
>> merely transpose neighbouring chars some ARG chars away.
>
> And what if the user decides to bind a different keystroke to 
> universal-argument?

True, from this point of view it's a very bad idea, C-u would be not
customisable any longer.  But I think it's only a marginal problem and
on the other hand I feel the need to expand the Emacs key-binding
space, this is my only idea so far and I will test its feasibility.

Thanks

-- 
    Best wishes

    H. Dieter Wilhelm
    Darmstadt, Germany

Re: How to detect C-u supplied arguments from other prefix arguments

[Stefan Monnier]

> I'd like to detect whether prefix arguments of a command are supplied
> by C-u or otherwise.

> My idea is to use this-command-keys and compare it to some string,
> like the following pseudo code:

> (defun bla (arg)
>   (interactive "p")

Use (interactive "P") and then `arg' will have different shapes in the
different cases: either nil, or a number (if entered via C-u N1 N2 N3, or
via C-N1 C-N2 C-N3), or a one-element list containing a number 4^N if
entered via sequence of N times C-u.


        Stefan

Re: How to detect C-u supplied arguments from other prefix arguments

[Dieter Wilhelm]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> I'd like to detect whether prefix arguments of a command are supplied
>> by C-u or otherwise.
>
>> My idea is to use this-command-keys and compare it to some string,
>> like the following pseudo code:
>
>> (defun bla (arg)
>>   (interactive "p")
>
> Use (interactive "P") and then `arg' will have different shapes in the
> different cases: either nil, or a number (if entered via C-u N1 N2 N3, or
> via C-N1 C-N2 C-N3), or a one-element list containing a number 4^N
> if

By the way C-N1 N2 N3 works as well as C-N1 C-N2 ...

> entered via sequence of N times C-u.

Sorry, I wasn't precise, I meant to distinguish also when supplying
numbers: Between C-u furnished and C- or M- furnished prefix arguments.
I'll work now with the hint from Johan Bockgård

    (eq ?\C-u (aref (this-command-keys) 0))

Thanks

-- 
    Best wishes

    H. Dieter Wilhelm
    Darmstadt, Germany