Re: What am I doing wrong?

[John Harper <jsh unfactored org>]

Hi,

On Sep 24, 2004, at 1:19 AM, Rohan NIcholls wrote:
> I have a problem that probably has to do with my not understanding the
> semantics of first-class objects, and calling them.  Or something as
> stupid as a syntax error.
>
> Here is macro to map a workspace to a key
>
> (defmacro map-workspace ( num )
>   (let ((g-num (gensym)))
>     (let ((g-num num))
>       `(bind-keys global-keymap ,(concat "M-" (number->string g-num)) 
> '(activate-workspace ,g-num)))))

there's no real reason to write this as a macro, e.g. since it doesn't 
rely on `num' not being evaluated in some cases, so you could easily 
turn it into a function:

(defun map-workspace (num)
  (bind-keys global-keymap (concat "M-" (number->string num)) 
`(activate-workspace ,num)))

> then because I am really lazy I thought I would do this:
> (defun map-workspaces ()
>   (do ((x 1 (1+ x)))
>       ((> x 7))
> ;;    (princ x)))
>      (map-workspace x)))
>
> This does not work, however if I switch it with the commented out
> princ statement it works.

the problem is that (map-workspace x) fails to macro-expand, since 
(number->string 'x) isn't valid, using the above function definition 
should work. (The reason it's 'x there is because macros see their 
arguments _before_ they are evaluated)

btw, to experiment with macros, it's useful to run rep and use the 
,expand command to see what the code they actually generate (that's how 
I worked out what's happening here)

	John