Re: Determine object passed as argument

On 2026-04-11 17:25, Heime wrote:
> On Sunday, April 12th, 2026 at 12:57 AM, Jean Louis <[email protected]> 
> wrote:
> 
>> On 2026-04-11 15:14, Heime wrote:
> 
>> > Can a function determine the object being passed as argument and
>> > print its name.  For instance that I passed if I pass fpln when
>> > calling (lana-du-fpln 'fpln).
>> >
>> > (defun lana-du-fpln (datenstruk &optional bname)
>> 
>> In Emacs Lisp, you cannot directly get the variable name that was 
>> passed
>> to a function, because arguments are evaluated before being passed. By
>> the time datenstruk receives the value, the original variable name is
>> lost.
>> 
>> (defun lana-du-fpln (datenstruk-symbol &optional bname)
>>    "Print the name of the symbol passed, then access its value."
>>    (message "Processing variable: %s" datenstruk-symbol)
>>    (let ((datenstruk (symbol-value datenstruk-symbol)))
>>      ;; Now work with datenstruk's value
>>      (message "Value: %S" datenstruk)))
>> 
>> Call it with quoted symbol: (lana-du-fpln 'fpln)
> 
> The above gives "Warning: lana-fpln is unbound (void variable)"

that is correct, it is for you to do something with it.

>> (defun lana-du-fpln (datenstruk-symbol &optional bname)
>>    "Print the name of the symbol passed, then access its value if 
>> bound."
>>    (message "Processing variable: %s" datenstruk-symbol)
>>    (if (boundp datenstruk-symbol)
>>        (let ((datenstruk (symbol-value datenstruk-symbol)))
>>          (message "Value: %S" datenstruk)
>>          ;; Your logic here
>>          )
>>      (message "Warning: %s is unbound (void variable)"
>> datenstruk-symbol)))
>> 
>> "Warning: fpln is unbound (void variable)"
> 
> The above gives "Processing variable: fpln" followed by its value.
> 
> Why does the condition (if (boundp datenstruk-symbol) make things work 
> out?

The boundp check prevents the symbol-value call from throwing a "void 
variable" error when the symbol hasn't been defined, allowing the 
function to handle unbound variables gracefully instead of crashing.

-- 
Jean Louis