Re: undiagnosed pic error

[G. Branden Robinson]

Forwarding another mail of Doug's that I think was sent to TUHS by
mistake.

At 2023-06-13T21:58:51-0400, Douglas McIlroy 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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