Re: Return value not as expected in Emacs Lisp function

[Pascal J. Bourguignon]

Thorsten Jolitz <tjolitz@gmail.com> writes:

> and I ask myself what happened between the second-last and the last line of
> the function? I cannot reproduce this with a MWE, and the real function is too
> convoluted to present it here, so I keep the problem description on an
> abstract level. 

On an abstract leve, I can't debug a function if I don't have it's
code.  That's the reason d'être of the MWE, and by default the real code.


> I'm actually only interested in the result string as a return value, the
> message statement is just for logging. But why is the string produced by
> 'mapconcat' missing in the return value?

The real question is why you use mapconcat to produce a string
representation of a sexp?  Just use prin1-to-string!

(let ((list '((click NIL 1) (press NIL 1) (click NIL 4) (click NIL 1))))
  (prin1-to-string `(prog ,@list )))
--> "(prog (click NIL 1) (press NIL 1) (click NIL 4) (click NIL 1))" 

Notice:

- emacs lisp is a lisp-2, not a lst-1.

- NIL is true:
  
  (not (not 'NIL))       --> t
  (not 'NIL)             --> nil
  (if 'NIL 'true 'false) --> true


-- 
__Pascal Bourguignon__                     http://www.informatimago.com/
A bad day in () is better than a good day in {}.  
You know you've been lisping too long when you see a recent picture of George 
Lucas and think "Wait, I thought John McCarthy was dead!" -- Dalek_Baldwin