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From: raymond@pioneer.arc.nasa.gov.arpa (Eric A. Raymond)
Newsgroups: comp.lang.lisp
Subject: Re: Summing a list
Message-ID: <17109@ames.arc.nasa.gov>
Date: 26 Oct 88 02:51:41 GMT
References: <1131@amelia.nas.nasa.gov> <5671@eagle.ukc.ac.uk> <10794@srcsip.UUCP>
Sender: usenet@ames.arc.nasa.gov
Reply-To: raymond@pioneer.arc.nasa.gov.UUCP (Eric A. Raymond)
Organization: NASA Ames Research Center, Moffett Field, Calif.
Lines: 48

In article <10794@srcsip.UUCP> rogers@eagle.UUCP (Brynn Rogers) writes:
>
> I Have a silly question.   I need to take the sum of a list 
> of numbers.
> (SETQ NUMLIST '(1 2 3 6 7))
> This is quite simple, really, but what is the BEST way to do it?
> I like: 
> 
> (EVAL (CONS '+ NUMLIST))

Ugggggh!  It may seem novel but its a poor, outdated style of programming.
First you waste a cons cell, make your code very obscure, and force the code
to be interpreted.

> But someone else says this would be faster::
>  
> (LET ((SUM 0))
>    (DOLIST (NUM NUMLIST)
>       (SETQ SUM (+ SUM NUM))))  ;; or maybe (INCF SUM NUM)

Or any other itertive control structure

>
>
>of course, there is always:
>
>(DEFUN SUM (NUMLIST)
>   (COND ((NULL NUMLIST) 0)
>         (T (+ (FIRST NUMLIST) (SUM (CDR NUMLIST))))))
>
>    I think it's obvious that the last would be slow.

Not necessarily.

How about :

  (apply #'+ NUMLIST)

  or

  (reduce #'+ NUMLIST)


Name: Eric A. Raymond
ARPA: raymond@pioneer.arc.nasa.gov
SLOW: NASA Ames Research Center, MS 244-17, Moffett Field, CA 94035

Nothing left to do but :-) :-) :-)