Comments on: A kind of magic

By: Alex Ott

Alex Ott — Thu, 29 May 2008 11:59:07 +0000

You can also use libmagic via ffi? I think, that it will return more information, then your own code

By: Loop

Loop — Tue, 20 May 2008 12:09:34 +0000

Check out the thereis loop clause for your any-predicate macro.

By: Leslie

Leslie — Fri, 02 May 2008 09:07:33 +0000

Fixed, thanks.

By: foo

foo — Fri, 02 May 2008 07:34:45 +0000

You did not change it correctly. You need to do (LOOP FOR CHARACTER ACROSS STRING … ). ACROSS not in.

Also in the Macro the GENSYM is not needed.

Just use `(or ,@(loop for p in preds collect `(,p ,@args)))) as the body. The GENSYM would be needed, if your macro wants to introduce new symbols into the code. But it does not do that.

By: Leslie

Leslie — Fri, 02 May 2008 06:53:38 +0000

foo, thanks for your help. I added your simplifications to the code.

By: foo

foo — Thu, 01 May 2008 16:16:14 +0000

also check out:

(some (lambda (pred) (funcall pred file)) ‘(jpeg-p png-p gif-p))

By: foo

foo — Thu, 01 May 2008 16:10:23 +0000

You also don’t need to coerce the string to a list.

Use (loop for character across string … )

By: foo

foo — Thu, 01 May 2008 16:07:59 +0000

You also don’t need `(funcall (function ,p) ,@args) .

`(,p ,@args) is fine.

Anyway it is better not to use a macro.

By: Leslie

Leslie — Thu, 01 May 2008 13:30:29 +0000

Thanks for the remark on function designators.

I’m not sure why I passed a zero for EOF-ERROR-P (I wrote this some weeks ago), but it certainly is a mistake.

By: Zach Beane

Zach Beane — Thu, 01 May 2008 13:14:57 +0000

You don’t need to use SYMBOL-FUNCTION. A symbol is a valid function designator. You could make the call like this:

(any-predicate ‘(jpeg-p pnng-p gif-p exif-p) file)

The macro is really quite unnecessary.

Why did you pass 0 as EOF-ERROR-P in READ-BYTE?