Re: [boost] [challenge!] find a common domain

Subject: Re: [boost] [challenge!] find a common domain
From: Eric Niebler (eric_at_[hidden])
Date: 2010-05-19 18:14:14

On 5/19/2010 3:07 PM, Jeremiah Willcock wrote:
>>> In that case, when do two domains that
>>> both derive from default_domain conflict?  They have a common ancestor,
>>> namely default_domain.  Or should default_domain be special in that
>>> regard, with a rule such as "if the merger of two domains is
>>> default_domain but one of them isn't default_domain, replace the result
>>> with not_a_domain"?
>>
>> Close. Yes, default_domain is special. If the merger of two domains is
>> default_domain and /neither of them/ is default_domain, the result is
>> not_a_domain. Otherwise, the one that's not default_domain dominates.
>> So, if lambda_domain is a sub-domain of default_domain, it is stronger
>> than default_domain and should dominate. I.e., "_1 + 42" should be a
>> lambda expression.
>>
>> default_domain should *never* be the answer when any domain is not
>> default_domain.
> 
> What about in the case of two different domains that both derive from
> default_domain but have no other ancestors in common?  

Ambiguous. not_a_domain.

> I see
> not_a_domain in your test cases.  What about two different domains that
> each derive from DD0 (in your test case)?  What should the result of
> combining them be?  

DD0.

> For non-default_domain domains I use the least
> common ancestor (which is what it seemed like you wanted).

That works. Something like it should also work for the family of domains
rooted at default_domain, with a special case for when the result would
be default_domain itself.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com