[plt-scheme] redex question: use ordering to force determinism?

On Sep 8, 2008, at 11:48 AM, Shriram Krishnamurthi wrote:

> Then they wouldn't be relations, no?

Sure they would.  Functions aren't a subset of relations in your  
world?  I just want a more convenient way of specifying a relation  
with a particular set of constraints.

Anyhow, perhaps metafunctions do what I want.

Thanks!

John

> On Mon, Sep 8, 2008 at 2:41 PM, John Clements <clements at brinckerhoff.org 
> > wrote:
>> Redex is designed to handle one-to-many reduction relations  
>> gracefully.  Is
>> there some way to squelch this and specify that only the first  
>> applicable
>> rule is to be used?  That is, I would like to implicitly quantify  
>> each
>> reduction rule with a side-condition that specifies that none of the
>> textually earlier rules match.
>>
>> My conjecture is that no such mechanism exists, because the  
>> beginner.ss
>> example includes things like this:
>>
>> ((symbol=? 'x_1 'x_2) . ==> . ,(if (eq? (term x_1) (term x_2))  
>> (term true)
>> (term false)))
>>  ((side-condition (symbol=? v_1 v_2)
>>                   (or (not (and (pair? (term v_1))
>>                                 (eq? (car (term v_1)) 'quote)))
>>                       (not (and (pair? (term v_2))
>>                                 (eq? (car (term v_2)) 'quote)))))
>>   . e==> .
>>   "symbol=?: expects argument of type <symbol>")
>>
>>
>> ... yikes!
>>
>> Is there some reason not to allow relations to be ordered in this  
>> way?  Am I
>> missing some newer feature?
>>
>> Many thanks,
>>
>> John
>>
>>
>>
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