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Postings from December 2021
Op 19-12-2021 om 11:41 schreef Darren Duncan:
> On 2021-12-19 2:01 a.m., Martijn Lievaart wrote:
>>
>> So what does Excuse("unknown value") plus Excude("unauthorized)
>> return? You just reintroduced the same problem that made you decide
>> against NVL, unless I'm missing something.
>
> The answer is that attempting to do that fails because addition is not
> defined for Excuse values. For example, it could result in something
> like:
>
> Excuse("No_Matching_Routine_Found", "plus", [@_])
>
> That Excuse value can either be returned, or if desired, thrown as an
> exception.
>
> A key part of what makes this NOT N-valued-logic is that the result of
> trying to use some arbitrary non-existent routine with an Excuse value
> always returns the same base result, an Excuse of subtype
> "No_Matching_Routine_Found", with added info naming the name and
> arguments attempted, and that there is NOT logic to test every
> possible Excuse subtype to determine what kind of result to give.
>
> Basically an Excuse is an unthrown exception, and is treated similarly.
>
> In this context, the version where there is exactly the 1 singleton
> Unknown etc is analagous to die() always throwing the same generic
> exception "I died" without any further information.
>
Ahh, makes sense. I'm still not completely convinced it's a good idea
(nor saying it isn't!), but I agree you solved the original problem.
HTH,
M4
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