On Wed, Mar 11, 2009 at 2:08 PM, Bill Page <bill.p...@newsynthesis.org> wrote:
>
> On Wed, Mar 11, 2009 at 5:52 PM, Carl Witty wrote:
>> This sounds potentially very useful; but option 3 ("do a strict subset
>> of coercions/conversions, and stop otherwise") is also tricky to
>> implement. For instance, if you had a mode where GF(5)(3) == ZZ(3)
>> raised a ValueError exception, then "GF(5)(3) in ZZ" would be false in
>> that mode, where it's normally true; that doesn't seem like the sort
>> of difference that would be helpful during debugging :)
>>
>
> Yes, I would find this very helpful - particularly option 3.
>
> In that case why wouldn't
>
> GF(5)(3) in ZZ
>
> also return a ValueError?
Because the __contains__ method on Parent (inherited by ZZ)
specifically catches ValueError and translates it to False.
This can be fixed, of course; but this is only the example I knew of.
I would worry that there would be other parts of Sage that catch
exceptions and change their behavior. (There's a parallel discussion
on almost exactly this topic, under the subject "Coercion and
exception handling".)
Carl
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