Re: Constraints and Functional Dependencies

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 25 Feb 2007 21:57:13 GMT
Message-ID: <ZCnEh.1295$PV3.18148@ursa-nb00s0.nbnet.nb.ca>

paul c wrote:

> Bob Badour wrote:
>

>> ...
>> Simply put, b != {b} because the type of b is different from the type 
>> of {b}. Equating them would be the exact same error as equating {} 
>> with {{}}.
>> ...

>
> That may be right and sensible, but ignoring questions of syntax, I'm
> not yet sure of that as I still don't understand much of type theory for
> example that of TTM.

It is not a question of syntax. The semantics of types demand inequality for any two values with different most specific types. A set has a very different type from what it contains just as a forest is different from a tree or a flock is different from a goose.

I do believe there are times when TTM allows
> equality comparisons between different types but I don't know if this is
> allowed only for subtypes/supertypes.

TTM always allows the comparisons. If the values have different most specific types, the comparison simply evaluates to false.

> In any event, I didn't say any of this was important - it is just my
> little obsession to try to see singletons in a different light, even if
> that means upsetting the applecart that has been rolling along so well
> for so many years.

I suggest a more interesting question to ask is whether one should allow implicit type conversions between a singleton set and its contents. Another is whether one should allow implicit type conversions of any kind. Received on Sun Feb 25 2007 - 15:57:13 CST