Re: Types and "join compatibility"

André Næss wrote:
>
> ...
> But as I thought about this I realized that it would be much simpler
> to consider the basic operators. We should really just have to
> consider union, difference, restrict, project and product. Of these,
> the only one that requires us to think about types is clearly
> union. How to handle the case of union seems so obvious that I can't
> see any room for disagreement.
> ...

(btw, sorry i got the initial conclusion wrong, as Marshall pointed out.)

what you say above sounds very neat and appealing. am putting it on my list of things to ponder.

> ...
> The fact that the choice seems quite arbitrary troubles me a
> little.
> ...

it might be a "can't get there from here" kind of choice. although i'm an ignoramus about type theory, it seems to me so far that D&D's TTM approach is unabashedly from the point of view of the RM. if i've got it right, all they are saying in a way is that it is up for grabs how the RM would have to change if it didn't take the stance it does about subtypes. another way to put it is that it would be incumbent on anybody who says the contrary is compatible with the RM to write their own TTM!

> ...
> Amazon just sent me the dispatch confirmation, so I hope to find it in
> my mailbox on Monday.
> ...

you sound as if you've got a head for this stuff therefore i hope you'll buy TTM as well. it is also a very difficult read, at least for me, but its coherence, the way it hangs together and avoids contradicting itself, is rare. agreement is another thing - most of TTM is about what the RM means, not whether it is true or even likeable. (i haven't lived in a city yet where i could find books like that in the public or university libraries, so i had to buy it as well. most of the libraries seem to buy books that most people want which are usually the ones that are easy to read but not in the end very coherent. even though i'm getting shorter and shorter on dough, i'll be buying TTM, 3rd Ed. and cross my fingers that the cover is not upside down compared to the binding of the first edition I bought and so many other Addison-Wesley books I've had. still the upside-down cover was one of the very few incoherent things about it!)

paul c. Received on Fri Aug 05 2005 - 02:39:27 CEST