Explanation of macros; Haskell macros

[Rolf Wester]

mike420 at ziplip.com wrote:
> Let's say you do not have the "for" keyword, but you have
> "dolist" for iterating a list and "dotimes" - a simple 
> index loop. You want to create "for" just like in Python, and
> you also want "for i in range(10000): print i" to be efficient
> and avoid constructing the big list (maybe you do not have
> enough memory). In Lisp, you can acomplish this with the
> following macro:
> 
> (defmacro for(i in list &rest rest)
>   (if (eql 'in in)
>     (if (and (listp list)
>              (eql (length list) 2)
>              (eql 'range (first list))
>              (integerp (second list)))
>       `(dotimes (,i ,(second list)) , at rest)
>       `(dolist (,i ,list) , at rest))
>     (error "syntax error")))
> 
> 
What will a Pythonista think about Lisp macros when he/she tries:

(defun f (n)
   (for i in (range n)
        (print i)))
(f 10000)

Maybe the macro should better be written:

(defmacro for (i in list &rest rest)
   (if (eql 'in in)
     (if (and (listp list)
              (eql (length list) 2)
              (eql 'range (first list))
              (or (integerp (second list)) (symbolp (second list))))
       `(if (integerp ,(second list))
		   (dotimes (,i ,(second list)) , at rest)
		   (error "not an integer"))
       `(dolist (,i ,list) , at rest))
     (error "syntax error")))


Rolf Wester