On 1/8/04 6:50, Nick Cox wrote
[snip...]
If the lazy evaluation model were used, 'or' would be true as long as at
least one is true, and 'and' would be false if at least one is false.
Extending this with the normally unnecessary extensions that 'or' is
false if all are false, and 'and' is true if all are true would give a
nice logical way to work.
>
>1. fill in truth tables
>
& true false irrelevant
true T F I
false F F F
irrelevant I F I
>
| true false irrelevant
true T T T
false T F I
irrelevant T I I
This still keeps the !(A|B) = (!A) & (!B) and the !(A&B) = (!A) | (!B)
working fine, as well as the distributive laws.
It would be like treating '&' as 'min' and '|' as 'max' while 't' would
be 1, 'f' would be 0, and 'irrelevant' would be 1/2, instead of + or -
infinity. This would then screw up any fuzzy logic routines that would
ever be built in the future.
I'd think this would be very easy to explain, BUT Nick's point about it
being far too late to change is well taken. Stata's current
implementation surely speeds up execution by a lot, since C uses lazy
evaluation, which means that as few logical statements are evaluated as
possible. I guess I'll just blame Boole, as suggested.
Bill
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