Re: Implementation of boolean types.

Marshall,
Symbolic programming is a good solution for null values. See these trivial evaluations:
y = 1+x --> 1+x
y - x --> 1

z = (1,1,x) --> 2 + x
z - x -->2

False and x --> False

True or y --> True
a = not b --> not b
c = not a --> b

Remember elementary algebra: We learned how to calculate with unknowns in elementary school :-)) But CS forgot to build it in computing. I strongly believe CAS [Computer Algebra Systems] are needed for solving the null problem.

The practical problem is that expressions with "unknown variables" (symbols) tend to get really big
(e.g. z + y --> (2 + x) + (1+x) -->3 + 2x).

Greeting from Craotia,
Drago Ganic

"Marshall Spight" <marshall.spight_at_gmail.com> wrote in message news:1121534821.846347.260300_at_o13g2000cwo.googlegroups.com...
> Mikito Harakiri wrote:
>> Tony Andrews wrote:
>> > That would be a dumb treatment, really. NULLs propagate in
>> > computations for numbers, because it makes sense to do so: we really
>> > don't know what 1+NULL is equal to.
>>
>> Not quite: 1+NULL = NULL while sum(1,1,NULL) = 2
>> No elementary consistency.
>
> yeah, that's really weird. the 1+null case shows null
> having 'unknown' semantics. the sum(1,1,null) case shows
> null having 'missing value' semantics. So which is it?
> Clearly, there is no particular consistency.
>
> I would prefer a treatment with better consistency.
> In particular, I see value in using 'missing value'
> semantics, because how they should behave is quite
> clear, whereas unknown introduces 3vl which I find
> unattractive, from the standpoint that it introduces
> a lot of complexity for little payback. I also think
> that unknown semantics are better handled by user-defined
> special values.
>
>
> Marshall
>
Received on Sun Jul 17 2005 - 17:33:58 CEST