Re: [Scheme-reports] multiple returns from map functions?

["Aaron W. Hsu" <arcfide@x>]

On Thu, 05 May 2011 11:43:53 -0400, <xacc.ide@x> wrote:

> The brings up the question whether list control procedures can accept  
> cyclic
> lists.

> Should the following be valid?

This is interesting, normally, `map' is specifically not allowed to take  
circular lists and you get an error when trying to deal with them.  
However, that is partly because of the restriction prior to this that all  
arguments should be of the same length. Now, I think, there is an  
opportunity to consider `map' in different terms. Whether we should do  
this or not is still up to question.

We could allow map to contain circular lists. This would make certain  
paradigms easier. If we did such a thing, i think we would also need to  
require that should map receive arguments that are all circular, it must  
return a circular list where each distinct element in the list has been  
"mapped." On the other hand, how much more difficult is doing this? Is it  
readily feasible? Is there any precedent for doing this before? I would  
not wish to do this if there is no precedent and if this does not reflect  
current standard practice; though I might encourage this form of map in  
experimentation outside of the standard.

	Aaron W. Hsu

-- 
Programming is just another word for the lost art of thinking.

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