[REBOL] Re: Correct Behaviour? Was False = 2 ????
From: joel:neely:fedex at: 2-Jul-2001 16:38
Hello, all,
Having already expressed some opinions (perhaps too many ;-)
in this area, I felt inclined to listen for a while. I
think there are a couple of points that haven't come up
that are worth considering.
[Robbo1Mark--aol--com] wrote:
> 1. Should Series! Index begin at Zero?
>
I'd rephrase as "What are the pro/con tradeoffs for having
series indices begin at 0 or 1? If there are advantages
to having 0-origin indexing, do those advantages outweigh
the effort of conversion of existing code?"
Let me pose a practical programming question: given
>> a: [2 3 5 7 11 13 17 19] == [2 3 5 7 11 13 17 19]
>> b: at a 5 == [11 13 17 19]
>> c: at b 3 == [17 19]
what is the relationship between A and C? I.e., what
value of X makes
pick a x
equivalent to
pick c 2
Answering this question (or explaining the answer) in a 1-origin
scheme (actually, any non-0-origin scheme) seems to involve the
distinction between absolute indices and relative indices, which
combine according to the following rules:
absolute - absolute is relative
absolute + absolute is useless/misleading
relative +/- relative is relative
absolute +/- relative is absolute
The relative index of B in A is (5 - 1). The relative index
of C in B is (3 - 1). Therefore, the absolute index of C/2
in A is (5 - 1) + (3 - 1) + (2 - 1) + 1 = 8.
If all indexing were 0-origin, the distinction between absolute
and relative indexes goes away. The above example would have
read
;; a: [2 3 5 7 11 13 17 19] == [2 3 5 7 11 13 17 19]
;; b: at a 4 == [11 13 17 19]
;; c: at b 2 == [17 19]
and the position of C/2 relative to A would be 4 + 2 + 2 = 8.
Remember that it wasn't until western civilization gave up the
1-origin Roman numerals and began using the 0-origin decimal
system that arithmetic really began the uphill climb to becoming
Mathematics.
> 2. Should 0, None & False be equivalent
> for 'PICKing values from a series! and
> return the FIRST or index 0 value whereas
> True and 1 would return the SECOND or
> Index 1 value?
>
There's another lurking inconsistency, which has nothing to do
with converting to/from integers. Consider that
>> logblk: reduce [
[ 1 < 2 1 > 2 2 < 1 2 > 1
[ ] == [true false false true]
>> sort logblk == [false false true true]
Doesn't it seem odd that SORT thinks that FALSE precedes TRUE,
and yet PICK thinks that FALSE *follows* TRUE? Surely the
ordering of values within a type is a meaningful concept,
whether or not we try to convert to/from some other type?
--
It's turtles all the way down!
joel'dot'neely'at'fedex'dot'com
