Re: Passing a list of symbols to function argument

[Stephen Berman]

On Fri, 29 Nov 2024 20:15:04 +0000 Heime <heimeborgia@protonmail.com> wrote:

> Sent with Proton Mail secure email.
>
> 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