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

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