Re: Passing a list of symbols to function argument

[Stephen Berman]

On Fri, 29 Nov 2024 21:16:09 +0000 Heime <heimeborgia@protonmail.com> wrote:

> On Saturday, November 30th, 2024 at 8:41 AM, Stephen Berman
> <stephen.berman@gmx.net> wrote:
>
>> On Fri, 29 Nov 2024 20:15:04 +0000 Heime heimeborgia@protonmail.com wrote:
>>
>> > On Saturday, November 30th, 2024 at 7:54 AM, Stephen Berman
>> > stephen.berman@gmx.net wrote:
>> >
>> > > On Fri, 29 Nov 2024 17:34:01 +0000 Heime via Users list for the GNU Emacs
>> > > text editor help-gnu-emacs@gnu.org wrote:
>> > >
>> > > > Why do I get
>> > > >
>> > > > Wrong type argument: stringp, tabtrail
>> > > >
>> > > > When using the call
>> > > >
>> > > > (poalatuk '(72 tabtrail global))
>> > > >
>> > > > to the function
>> > > >
>> > > > (defun poalatuk (actm-seqr)
>> > > >
>> > > > (interactive
>> > > > (let* ( (colw (read-number "Line Column: " 72))
>> > > > (cseq '("extended" "disable" "tabtrail"))
>> > > > (rsel (completing-read "Selector: " cseq nil t "tabtrail"))
>> > > > (scope (completing-read "Scope: "
>> > > > '("global" "local") nil t "local")) )
>> > > >
>> > > > ;; Pass a single list as argument
>> > > > (list (list colw rsel scope))) )
>> > > >
>> > > > ;; -------------------------------------------------------------
>> > > >
>> > > > (message "poalatuk: %S" actm-seqr)
>> > > >
>> > > > (let* ( (colw (nth 0 actm-seqr)) ;; Extract column width.
>> > > > (rsel (intern (nth 1 actm-seqr))) ;; Extract mode selector.
>> > >
>> > > ^^^^^^^^^^^^^^^^^^^^^^^^^^
>> > >
>> > > The error happens here. You passed '(72 tabtrail global) as the value
>> > > of the argument actm-seqr, so (nth 1 actm-seqr) returns the symbol
>> > > `tabtrail'. But` intern' takes a string and returns the symbol (in the
>> > > obarray) whose name is given by the string.
>> > >
>> > > Steve Berman
>> >
>> > I want the function to accept both symbols and strings. intern must then
>> > be applied only when a string is passed. Which undoubtedly needs a 
>> > conditional
>> > check.
>> >
>> > Perhaps I should also test whether the argument is a symbol or do the if
>> > and pcase handle errors (because the commands will be skipped).
>> >
>> > (let* ((colw (nth 0 actm-seqr))
>> > (rsel (if (stringp (nth 1 actm-seqr))
>> > (intern (nth 1 actm-seqr))
>> > (nth 1 actm-seqr)))
>> > (scope (if (stringp (nth 2 actm-seqr))
>> > (intern (nth 2 actm-seqr))
>> > (nth 2 actm-seqr))))
>>
>>
>> This seems fine; `if' does not do error handling, nor does` pcase' AFAIK
>> (but there are several variants and extensions of pcase, and I'm not too
>> familiar with them, so maybe some of them do error handling), but
>> `condition-case' is the basic error handling form in Elisp. Alternatively,
>> since the error only happens in noninteractive calls (since interactive
>> calls use` completing-read', which returns strings),
>> you could condition on `called-interactively-p'.
>>
>> Steve Berman
>
> For the interactive call I want to pass the three values so that
> actm-seqr will be a list of three objects.
>
> Thus I do
>
>    (list (list colw rsel scope))
>
> Would the above be correct?

Yes.

> With only (list colw rsel scope) emacs does complain.

Because that means the interactive call passes three arguments, but your
definition of `poalatuk' only specifies one argument parameter.

> I wonder whether actm-seqr will give me ((72 tabtrail global))
> and not (72 tabtrail global).

I don't know what you mean; actm-seqr is the function parameter, a
variable whose value is whatever is passed on calling the function
either interactively or noninteractively.

> Have also been looking at the possibility of using
>
>    (list (list colw (intern rsel) (intern scope)))
>
> Or would this be considered replication?  Because the call
> to intern would happen later anyway.

Then it would cause the error you reported in your OP.

Steve Berman