simple... bug?

simple... bug?

[Joe Corneli]

(defun squares (list-of-numbers)
  (let ((list-of-squares nil)
  (i 0)
  (L (length list-of-numbers)))
    (while (< i L)
      (setq list-of-squares (append list-of-squares 
				        (list (* (nth i list-of-numbers)
							     (nth i
  list-of-numbers)))))
      (setq i (1+ i))))
  list-of-squares)

For

(squares '(2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79
83 89 97))

I get

     *
(4 9 9 25 49 121 169 289 361 529 841 961 1369 1681 1849 2209 2809 3481
3721 4489 5041 5329 6241 6889 7921 9409)


Emacs is 21.3.1
OS is  Mac OS X 10.3


	      Am I making some _extremely_ subtle mistake?

--
Joe
-*-
The technological simulacrum creates its own reality,
which Baudrillard calls the "hyperreal," a kind of ersatz
parody of Plato's ideal world of forms.  fusionanomaly.net

Re: simple... bug?

[Alan Mackenzie]

Joe Corneli <jcorneli@math.utexas.edu> wrote on Tue, 14 Oct 2003 02:17:11
-0500:

> (defun squares (list-of-numbers)
>   (let ((list-of-squares nil)
>   (i 0)
>   (L (length list-of-numbers)))
>     (while (< i L)
>       (setq list-of-squares (append list-of-squares 
> 				        (list (* (nth i list-of-numbers)
> 							     (nth i
>   list-of-numbers)))))
>       (setq i (1+ i))))
>   list-of-squares)

> For

> (squares '(2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79
> 83 89 97))

> I get

>      *
> (4 9 9 25 49 121 169 289 361 529 841 961 1369 1681 1849 2209 2809 3481
> 3721 4489 5041 5329 6241 6889 7921 9409)


> Emacs is 21.3.1
> OS is  Mac OS X 10.3

> 	      Am I making some _extremely_ subtle mistake?

What on earth is the value "list-of-squares" that you're returning?  It's
not the one you bound in the "let" form.  :-)

Hey, I do things like this too.  It makes me feel really stupid.
Something I've done approximately three times in the last three months is
to write this form:

(\= (point) here)

It didn't do what I wanted.  But thank goodness for edebug.  :-(

> Joe

-- 
Alan Mackenzie (Munich, Germany)
Email: aacm@muuc.dee; to decode, wherever there is a repeated letter
(like "aa"), remove half of them (leaving, say, "a").

Re: simple... bug?

[Joakim Hove]

Joe Corneli <jcorneli@math.utexas.edu> writes:

> (defun squares (list-of-numbers)
>   (let ((list-of-squares nil)
>   (i 0)
>   (L (length list-of-numbers)))
>     (while (< i L)
>       (setq list-of-squares (append list-of-squares 
> 				        (list (* (nth i list-of-numbers)
> 							     (nth i
>   list-of-numbers)))))
>       (setq i (1+ i))))
>   list-of-squares)

Hello,

as already pointed out by Alan the "list-of-squares" variable is out
of scope when you return it, so I *guess* it is only accidental that
it is so seemingly correct. Moving a closing parenthesis to include
the return value  within the let block should solve your problem:

  list-of-numbers)))))
      (setq i (1+ i)))
  list-of-squares ) )
                  ^ 
                 / \
                Matches the (let  )



Anyway, a simpler solution:

(defun squares (nr-list)
  (mapcar '(lambda (x) (* x x)) nr-list))

Use C-h f mapcar to learn about the function mapcar.


HTH - Joakim



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Re: simple... bug?

[David Vanderschel]

"Joe Corneli" <jcorneli@math.utexas.edu> wrote in message
news:mailman.1649.1066115958.21628.help-gnu-emacs@gnu.org...
>       Am I making some _extremely_ subtle mistake?

Not all that subtle, but easy to do.  What surprises
me is that Joe's mistake did not cause an error
message.  When I try Joe's function, I get

   Signaling: (void-variable list-of-squares)

Ie., the function does not even execute successfully.
I suspect that Joe had also created an instance of
list-of-squares at top level and its value is the one
being returned.

Joe, I think you could have easily resolved your
symptom had you tried stepping through the code with
edebug.  edebug is your friend!  :)

Regards,
  David V.