[pdpi]

To be honest? Yes, I did make it up on the spot, because my reaction to the post was "there has to be a better way to interpret bitwise AND operating on decimals". What I cared about was that we could build some sort of extension for bitwise AND that operated on any base in a completely consistent way, with no considerations for whether that interpretation is in widespread use.

I must confess to being quite chuffed that homegarlic has since commented that this is consistent with how Zadeh fuzzy set theory works (though that uses reals in the [0,1] range rather than modular arithmetic).

[saynsedit]

With all due respect, digit-wise MIN seems like an unnecessary abstraction in same vein as AbstractManagerFactoryFactory.

If the abstraction doesn't have generally applicable higher-level properties, it's probably not worth abstracting.

After all, bit-wise AND is only one of 16 possible two-argument bit functions. Shall we create a digit analog for all 16 of them?

[pdpi]

As other people have said in this thread, the interpretation of AND and OR as MIN and MAX respectively _is_ a useful one, and it sees applications in fuzzy logic.

Given that, looking at decimal digit-wise AND under that lens isn't about introducing a new abstraction, it's about applying an existing abstraction to a new domain.

[saynsedit]

One litmus test to check the usefulness of an abstraction is to see if it conforms to existing laws of the specific case.

Let's use distributivity of AND over OR:

    a & (b | c) = a & b | a & c

This also works in the abstraction of Boolean algebra to normal algebra:

    a * (b + c) = a * b + a * c

What about with your digit MIN/MAX abstraction:

    MIN(a,MAX(b,c)) = MIN(MAX(a,b),MAX(a,c))

Well... No, this does not generally hold. If b and c are both larger than a, then this equality fails.

Distributivity is a pretty important property. Without it, your MIN/MAX algebra just has commutivity and associativity which arguably aren't very unique considering all other possible commutive/associative functions. In any case, losing a property dramatically decreases the usefulness of your algebraic abstraction.

Another wart in your abstraction is the missing NOT operation, further deteriorating its usefulness.

Just because the MIN abstraction works for the AND case, that's not enough to make it a worthwhile abstraction. What happens when you want to do more complex yet natural operations like a & (b | c)? In the same vein, AbstractManagerFactoryFactory may seem elegant now, but it may make it harder for new code to do trivial things down the road.

[jonsen]

I think it works, if you do it right:

  MIN(a,MAX(b,c)) = MAX(MIN(a,b),MIN(a,c))

[saynsedit]

It does, I stand corrected.

[jonsen]

And so does

  MAX(a,MIN(b,c)) = MIN(MAX(a,b),MAX(a,c))

so it is even more useful than normal algebra :p