Re: Determine object passed as argument

On Sunday, April 12th, 2026 at 5:17 PM, Jean Louis <[email protected]> wrote:

> 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.

Understood - you display a message when boundp is nil. 
 
> --
> Jean Louis
> 
>