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From: Kaz Kylheku <k...@kylheku.com>
Newsgroups: comp.lang.lisp
Subject: Re: Loop puzzle
Date: Mon, 27 Feb 2012 10:56:30 +0000 (UTC)
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On 2012-02-26, WJ <w_a_x_...@yahoo.com> wrote:
> Helmut Eller wrote:
>
>> I tried this code:
>> 
>> (let ((a '(x y)))
>>   (loop for a in '((a b) (0 1))
>>         for b in a
>>         collect (list a b)))
>> 
>> and expected that it evaluates to '(((a b) a) ((0 1) b)) but all the
>> implementations I tried return nil.  
>
> MatzLisp:
>
> it = [[:a, :b], [0, 1]]
> it.zip( it.first )
>     ==>[[[:a, :b], :a], [[0, 1], :b]]

TXR Lisp's has the sequential binding Helmut Eller was looking for in loop:

 (collect-each* ((i '((a b) (0 1)))
                 (j (first i)))
   '(,i ,j))

This collect-each* can easily be ported to Common Lisp as a macro.