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From: rgo on 28 Feb 2010 12:04
Hi!
Here is some code:
(let ((a 0) (b 1) (c 2) (d 3))
(loop
for i in '(wood clay iron food)
do (format t "~A:~D~%" i (symbol-value i))))
Seems as a working code, but sbcl writes "The variable [ABCD] is
defined but never used.", and when code executes an error "The
variable A is unbound" arrives.

I think, that variable is unboud because sbcl optimized it out, isnt
it? And how can i dismiss such an optimization?
From: Giovanni Gigante on 28 Feb 2010 12:26
rgo wrote:
> Hi!
> Here is some code:
> (let ((a 0) (b 1) (c 2) (d 3))
> (loop
> for i in '(wood clay iron food)
> do (format t "~A:~D~%" i (symbol-value i))))
> Seems as a working code, but sbcl writes "The variable [ABCD] is
> defined but never used.", and when code executes an error "The
> variable A is unbound" arrives.

I presume that '(wood clay iron food) should read '(a b c d), otherwise
I do not understand what you're trying to do.
Anyway, remember that
"symbol-value cannot access the value of a lexical variable".
http://www.lispworks.com/documentation/HyperSpec/Body/f_symb_5.htm#symbol-value
From: rgo on 28 Feb 2010 13:13
On 28 фев, 20:26, Giovanni Gigante <g...(a)cidoc.iuav.it> wrote:
> I presume that '(wood clay iron food) should read '(a b c d), otherwise
> I do not understand what you're trying to do.
Yes. I tried to simlpify code and make a mistake. Sorry.

Thanks for replies!
From: John Thingstad on 28 Feb 2010 18:54
The Sun, 28 Feb 2010 18:31:41 +0100, Pascal J. Bourguignon wrote:

>
> Try this instead:
>
> (defvar *wood* 0)
> (defvar *clay* 1)
> (defvar *iron* 2)
> (defvar *food* 3)
>
> (loop
> :for i :in '(*wood* *clay* *iron* *food*) :do (format t "~A:~D~%" i
> (symbol-value i)))
>
>
>
> or this:
>
> (defmacro ref (var)
> `(lambda (m)
> (ecase m
> ((:name) ',var)
> ((:value) ,var))))
> (defun name (ref) (funcall ref :name)) (defun value (ref) (funcall ref
> :value))
>
> (let ((a 0) (b 1) (c 2) (d 3))
> (loop
> :for i :in (list (ref a) (ref b) (ref c) (ref d)) :do (format t
> "~A:~D~%" (name i) (value i))))

Wouldn't a plist be better?

(loop for (key value) over (list :wood 0 :clay 1 :iron 2 :food 3) do
(format t "~A:~D~%" key value))

I find plist make a good subtitution for enumerated types and they have
better performance than hashtables for a small number of elements like a
database entry.



--
John Thingstad
From: John Thingstad on 28 Feb 2010 19:00
The Sun, 28 Feb 2010 17:54:15 -0600, John Thingstad wrote:

> Wouldn't a plist be better?
>
> (loop for (key value) over (list :wood 0 :clay 1 :iron 2 :food 3) do
> (format t "~A:~D~%" key value))
>
> I find plist make a good subtitution for enumerated types and they have
> better performance than hashtables for a small number of elements like a
> database entry.

sorry should test my code first... this works as intended:

(loop for (key value) on (list :wood 0 :clay 1 :iron 2 :food 3) by #'cddr
do (format t "~A:~D~%" key value))



--
John Thingstad
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