[TUHS] Re: undiagnosed pic error

[Marc Donner <marc.donner@gmail.com>]

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How sparse is the 35x35 matrix?  For comprehensibility would it be the best
way to do it?

On Tue, Jun 13, 2023 at 9:59 PM Douglas McIlroy <
douglas.mcilroy@dartmouth.edu> wrote:

> There may be a simple generic way to correct pic's habit of accepting
> any set of object modifiers on any object, but obeying only a
> compatible subset.
>
> Pic already collects a bit vector of modifier types attached to the
> current object. If that were extended with a few more bits that
> designate the object types, the size, B, of the bit vector would be
> about 35--an easy fit in one 64-bit word. Then a BxB bit matrix could
> record both modifier/modifier incompatibilities and object/modifier
> incompatibilities. The collected bit vector needs to be tested against
> the matrix once per object definition.
>
> It seems to be harder to catch duplication of modifiers, requiring
> extra code at all points where bits are set. Nevertheless, this kind
> of error also merits detection.
>
> Some questions
>
> Does anybody think the issue is not worth addressing?
>
> Is there a better scheme than that suggested above?
>
> Is the scheme adequate? It would not, for example, catch a three-way
> incompatibility that does not entail any pairwise incompatibility,
> should such an incompatibility exist.
>
> Any other thoughts?
>
> Doug
>
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