On 5/19/2010 2:47 PM, Jeremiah Willcock wrote:
On Wed, 19 May 2010, Eric Niebler wrote:
On 5/19/2010 2:25 PM, Jeremiah Willcock wrote:
How do the rules for default_domain (and domains derived from it) fit into that picture? Expressions from different domains not derived from default_domain produce not_a_domain in the case of conflicts,
Right.
while a pair in which one element is derived from default_domain will always choose that element as the domain of the new expression.
Here, you mean "the other element" -- that is, the domain that is not a sub-domain of default_domain. The family of domains rooted at default_domain is weaker than all others.
OK. I implemented it the other way around -- choose the default_domain-derived domain if the other one isn't derived from that base. The two cases to flip to fix that are the second and third specializations of deduce_domain2_cases.
OK.
In my implementation, if both domains derive from default_domain but are otherwise incompatible, the result will be default_domain,
That's not right for the reason I stated above. And that's the case that hung me up for a while.
What do you want there? not_a_domain?
Yes.
Is default_domain itself a domain that's accessible to users (i.e., they can have an element with default_domain as its domain)?
Yes.
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. Gotta pass all the test cases I sent! :-)
but normal domains do not derive from default_domain and so end up with the not_a_domain behavior in the case of conflicts.
This part is right.
OK.
-- Eric Niebler BoostPro Computing http://www.boostpro.com