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Subject: Re: [boost] [challenge!] find a common domain
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2010-05-19 18:07:46

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

-- Jeremiah Willcock

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