Re: identity function with an echo side effect

[Pascal J. Bourguignon]

bolega <gnuist006@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.html
 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.

Only macros receive their arguments un-evaluated, which could be
characterized as an "implicit quotation".


-- 
__Pascal Bourguignon__                     http://www.informatimago.com/