* Choosing interactively from a list
@ 2014-12-07 2:58 Florian v. Savigny
2014-12-07 3:33 ` John Mastro
0 siblings, 1 reply; 7+ messages in thread
From: Florian v. Savigny @ 2014-12-07 2:58 UTC (permalink / raw)
To: help-gnu-emacs
Hi there everybody,
I would like to do something which seemed easy to me at first glance,
but is now proving mysteriously difficult:
I have a list, say ("A" "B" "C" "D" ... "Z" "a" "b" "c" "d"
... "z"). I also have an index, say 13. I would like to choose an item
from this list in the minibuffer, and be able to go forward and
backwards in this list, starting from the index, i.e. here, 13.
In other words, if the list goes on alphabetically as hinted above, the
element with the index 13 would be the string "N". I would like to
have "N" as the initial input in the minibuffer, and I would like to
go back (i.e. "M", "L", "K" - you name it) with some key and forth
(i.e. "O", "P", "Q" and so on).
I tried to do this with the usual minibuffer functions, and it almost
works, but not completely as I would like it:
(defun choose-from-list (list &optional index)
"Choose an item from LIST in the minibuffer.
Use a copy of LIST as history list, i.e. do not modify LIST.
Optional arg INDEX means start in the list at index INDEX."
(let ((reverse-list (reverse list))
(reverse-ind (- (length list) index))
(history-length t))
(read-from-minibuffer "Choose: "
(nth index list)
nil
nil
(cons 'reverse-list reverse-ind))))
(setq list
(list "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "O" "P" "Q" "R" "S" "T" "U" "V" "W" "X" "Y" "Z"
"a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "o" "p" "q" "r" "s" "t" "u" "v" "w" "x" "y" "z"))
(choose-from-list list 13)
This does exactly what I want, i.e. hitting M-p gets me one item back
in the list; M-n gets me one item forward. However, I would like to
require that the user (me) cannot change the value from the list, only
pick it. Thus, I have tried completing-read instead of
read-from-minibuffer, because completing-read has REQUIRE-MATCH:
(defun choose-from-list-cmplr (list &optional index)
"Choose an item from LIST in the minibuffer.
Use a copy of LIST as history list, i.e. do not modify LIST.
Optional arg INDEX means start in the list at index INDEX."
(let ((reverse-list (reverse list))
(reverse-ind (- (length list) index))
(history-length t))
(completing-read "Choose: " list
nil
t
(nth index list)
(cons 'reverse-list reverse-ind))))
I imagine this should be the same thing as regards the minibuffer
history, but here, the history cycling is somehow different: Although
I get the same list element as initial input, hitting M-n now gives me
the item at the *beginning* of the list ("A"), M-p gives me the item
at the *end*.
Can somebody explain that to me? An important aspect might be that I
am not really looking for completion, but rather rigid cycling through
a fixed list. And the whole approach, i.e. using the history for
something that is not really a history (and is not even supposed to be
modified like a history variable is), reversing it etc, feels very
roundabout and not as it should be.
Many thanks in advance!
Best regards,
Florian
--
Florian von Savigny
Melanchthonstr. 41
33615 Bielefeld
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Choosing interactively from a list
2014-12-07 2:58 Choosing interactively from a list Florian v. Savigny
@ 2014-12-07 3:33 ` John Mastro
2014-12-07 10:56 ` Choosing interactively from a list (starting off at any position) Florian v. Savigny
0 siblings, 1 reply; 7+ messages in thread
From: John Mastro @ 2014-12-07 3:33 UTC (permalink / raw)
To: help-gnu-emacs@gnu.org
Hi,
Florian v. Savigny <florian@fsavigny.de> wrote:
> I have a list, say ("A" "B" "C" "D" ... "Z" "a" "b" "c" "d"
> ... "z"). I also have an index, say 13. I would like to choose an item
> from this list in the minibuffer, and be able to go forward and
> backwards in this list, starting from the index, i.e. here, 13.
I don't know a way off-hand to do that without constructing a modified
version of the list (though I won't be surprised if someone chimes in
with one).
As an alternative, does this do something like what you're looking for?
(defun rotate-to-index (list index)
(append (cl-subseq list index)
(cl-subseq list 0 index)))
(defun choose-from-list-cmplr (list &optional index)
(completing-read "Choose: "
(if index (rotate-to-index list index) list)
nil
t))
--
john
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Choosing interactively from a list (starting off at any position)
2014-12-07 3:33 ` John Mastro
@ 2014-12-07 10:56 ` Florian v. Savigny
[not found] ` <CAOj2CQQ45gZpmuQUsMNp=iokkbB1Wz2cWpy6ZKfZ=BzyoSY6xg@mail.gmail.com>
0 siblings, 1 reply; 7+ messages in thread
From: Florian v. Savigny @ 2014-12-07 10:56 UTC (permalink / raw)
To: John Mastro; +Cc: help-gnu-emacs
Hi John,
thanks for your ideas!
> As an alternative, does this do something like what you're looking for?
>
> (defun rotate-to-index (list index)
> (append (cl-subseq list index)
> (cl-subseq list 0 index)))
>
>
> (defun choose-from-list-cmplr (list &optional index)
> (completing-read "Choose: "
> (if index (rotate-to-index list index) list)
> nil
> t))
Yes, this does work, but only forwards, not backwards. I would like to
go forwards with M-n and backwards (i.e. to the (index - 1)th element
of list) with M-p.
(It's interesting, BTW, that completing-read accepts an anonymous list
instead of a list variable name. It cannot possibly modify this
"history", can it?)
The practical context is that I have a long, long file which contains
a lot of dates in chronological order, some of which are usually past,
one perhaps today's date, and the rest is in the future. I would like
to devise a convenient and orderly method of jumping to any of these
dates, starting off at the most current date, i.e. either today's or
next. (It is actually much like moving back and forth in a calendar or
diary.)
I have written all of that, and with read-from-minibuffer, it works
fine, so there is no pressing need to solve it. (That the user can
enter non-existant dates is not a practical problem because I am the
user, and I know better.) I have just become really curious about why
the two functions seem to work differently with respect to the
minibuffer history.
On a more fundamental note, it has made me start wondering if
minibuffer completion and history might be worth supplementing with
further kinds of user input methods. (Because the minibuffer stuff is
really just a hack; that's not what histories are there for.)
In the problem I am working on, the ever-available completion is very
unhelpful - simply not the natural method of choosing -, because the
dates all start with one of just one, two or three different weekdays,
followed by the day of the month (still not unique). But whether the
date is one, two positions before or after today is almost always
relevant, because I am usually interested in the dates around today.
As Lisp is a list-processing language, it seems to me that an input
method which works like that should come easy to Emacs, and that
somebody might already have written something as basic as that. Does
anybody know of anything ... ?
Best regards!
Florian
--
Florian von Savigny
Melanchthonstr. 41
33615 Bielefeld
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2014-12-07 2:58 Choosing interactively from a list Florian v. Savigny
2014-12-07 3:33 ` John Mastro
2014-12-07 10:56 ` Choosing interactively from a list (starting off at any position) Florian v. Savigny
[not found] ` <CAOj2CQQ45gZpmuQUsMNp=iokkbB1Wz2cWpy6ZKfZ=BzyoSY6xg@mail.gmail.com>
2014-12-08 19:19 ` Fwd: " John Mastro
2014-12-08 22:51 ` Florian v. Savigny
[not found] ` <<87oardah6y.fsf@bertrandrussell.Speedport_W_723V_1_36_000>
2014-12-09 2:20 ` Drew Adams
2014-12-09 19:52 ` John Mastro
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