Re: identity function with an echo side effect

[bolega <gnuist006@gmail.com>]

On Aug 11, 7:19 am, p...@informatimago.com (Pascal J. Bourguignon)
wrote:
> bolega <gnuist...@gmail.com> writes:
> > On Aug 10, 4:03 pm, p...@informatimago.com (Pascal J. Bourguignon)
> > wrote:
> >> bolega <gnuist...@gmail.com> writes:
> >> > After searching google groups and emacs apropos extensively, I could
> >> > not find a function, perhaps I am missing one that can return
> >> > identically return its argument and has a small side effect of echoing
> >> > the argument in some place such as for example
>
> >> > the mini buffer or the point at which C-x C-e is typed.
>
> >> > For example, calling this function "echo" , usage would look like
> >> > this :
>
> >> > (cdr ( echo (cdr (echo (cdr (echo '(a b c d)))))))
>
> >> > echo:
> >> > '(a b c d) or (a b c d)  (I am not sure which would be appropriate)
> >> > (b c d)
> >> > (c d)
>
> >> > result:
> >> > (d)
>
> >> > Is there a need for quotes to prevent evaluation of alphabets at any
> >> > phase ?
>
> No.  Expressions are evaluated only by EVAL or LOAD (and at
> compilation time, compilation time expressions by COMPILE and
> COMPILE-FILE).  Otherwise, values are just values, they don't get
> evaluated magically (for what reason should they?)
>
> >> In Common Lisp, you can use PRINT for this.
>
> >> CL-USER> (cdr (print (cdr (print (cdr (print '(a b c d)))))))
>
> >> (A B C D)
> >> (B C D)
> >> (C D)
> >> (D)
> >> CL-USER>
> >> [...]
>
> > If you dont mind, how many years have you spent on learning emacs/
> > lisp ?
>
> 20 years.
>
> > Can you kindly give a reading syllabus, books list and possibly time
> > for completion from your perspective and what to get out of each book
> > since they have some common repetition.
>
> http://www.cliki.net/admin/search?words=books
>
> In particular, I like to advise:
>
>  Common Lisp: A Gentle Introduction to Symbolic Computation
>  http://www-cgi.cs.cmu.edu/afs/cs.cmu.edu/user/dst/www/LispBook/index....
>  http://www.cs.cmu.edu/~dst/LispBook/
>
> > Are there any implicit quotations taking place in the above sequence
> > of cdr, print ... ?
>
> Since CDR and PRINT are function, no implicit quotation occurs: the
> result values are directly passed as argument to the next function.

Then why does the following gives an error. Currently, I only have
elisp working so we confine to emacs runs.

(cdr (print (cdr (print (cdr (print (a b c d)))))))    C-x C-e

gives this error if I remove the quote. why ? I get errors if I remove
all prints. This means if the first cdr required quoted list, then the
rest must also require it. Hence, an implicit quotation might be
occurring as in setq ? Also, plz explain me the debugger output in
detail so I can figure it out myself. may be a line by line comment
and if there is a more comprehensive example you can cook, better for
all the readers, once and for all.

Debugger entered--Lisp error: (void-function a)
  (a b c d)
  (print (a b c d))
  (cdr (print (a b c d)))
  (print (cdr (print ...)))
  (cdr (print (cdr ...)))
  (print (cdr (print ...)))
  (cdr (print (cdr ...)))
  eval((cdr (print (cdr ...))))
  eval-last-sexp-1(nil)
  eval-last-sexp(nil)
* call-interactively(eval-last-sexp)



>
> Only macros receive their arguments un-evaluated, which could be
> characterized as an "implicit quotation".
>
> --
> __Pascal Bourguignon__                    http://www.informatimago.com/