I expected that I should be able to compile something like
\begin{spad}
)abbrev category APPROX Approximate
Approximate(X:Category):Category == X
++ mathematical properties are only approximate e.g. as in Float
\end{spad}
i.e. a category with a category parameter. Unfortunately I get a compile error:
>> System error:
The value |t#1| is not of type SEQUENCE.
If this did compile, then what I was hoping for was that as a category
Approximate(Ring) would have the same exports as Ring but would be
nominally different from Ring.
Then maybe we could arrange something like
Float has Ring
false
Float has Approximate(Ring)
true
Integer has Ring
true
Maybe also
Ring has Approximate(Ring)
true
Integer has Approximate(Ring)
true
>
> ... export something like ApproximateRing, but not Ring.
> But ApproximateRing is rather as useless as is our attribute
> Approximate, since the documentation is rather vague and doesn't clearly
> convey the semantics behind.
>
> ...
> Unfortunately, we cannot (yet) express in SPAD the respective
> mathematical laws. But what we can do is what we already do with the
> category CommutativeStar. We can introduce a category for every law that
> we find relevant.
> ...
>
>> In other words alternatives are:
>>
>> - have strict applicability conditions, but lie from
>> time to time
>> - tell truth always, but have loose applicability conditions
>
> Lying is not an option for me.
>
> Ralf
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