2008/4/8 Dirk Bergstrom <dirk@juniper.net>:

I want to write a rule that says "Find all long-eared dogs that do not have
short, black hair".  This seems like the simple way to do it:

collect( Dog( ears=="long", not (hair=="short" && color=="black") )

But that doesn't parse.  Some digging through the archives unearthed a mention
of De Morgan's laws, which leads to:

http://en.wikipedia.org/wiki/De_Morgan's_laws

Which explains that I can instead write:

collect( Dog( ears=="long", (hair!="short" || color!="black") )

Which, after some mental effort, turns out to be the right thing.

However, had I not found the reference to De Morgan's Law, it would have taken
me a long time to get there (if indeed I ever would have).  The end result is
also quite difficult to parse if you're not a logician, and thus not very
user-friendly.

Does anyone think it would be worthwhile to open a Jira requesting the ability
to negate a constraint group?  And, if I did open such a thing, do the
developers think it would be reasonably easy to implement?

--
Dirk Bergstrom               dirk@juniper.net
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