World: r4wp

Pekr, the reason it works for Python is because their series are 
always referenced from the start, so negative indices/offsets would 
otherwise have no meaning. REBOL has offset references to series, 
so negative indices/offsets already have a meaning for us.

s[0] is not confusing in C (even if newbies have sometimes issues 
with 0 itself), because C is 0-based.

Brian: except for the "learning new meaning" effort, do you see any 
other cons for having negative indexes work from tail?

The observation that we are using "a 1-based system" alone doesn't 
help you in any way with that.

I must have missed the proposal of BASIS?, but the fact that it would 
be a function or variable implies that it would be used to detect 
a global setting, like system/options/binary-base. Global settings 
like that have proven to be a universally bad idea in practice. Local 
settings are better.

In a pure 1-based system, you have neither 0 nor negative indices.

Agreed.

BrianH: BASIS? was proposed as the 0-based INDEX? dual.

Doc, it's not the "learning a new meaning", it's losing the meaning 
they already have. We need the meaning we have, we need to be able 
to reference offsets from before the current position.

Still the fact that `pick series 1` gives you the first item from 
current series position, makes the 0 position awkward.

Why?

0 is before 1, so pick 0 should give you the element before 1.

Actualy, as Ladislav repeatedly explained, having "pick -1" _not_ 
giving you the current element is just as awkward.

Andreas, oh good, whew. In R3 we're already having to replace all 
system options that affect MOLD with options to the MOLD function 
itself. It would be a shame to have to do the same for all of the 
indexing functions. Nonetheless, that meaning of BASIS? doesn't make 
sense for the name either, so I don't like it.

You can basically do:
- no 0 or negative indices at all

- disallow 0, have 1 return the next element forward, -1 the next 
element backward (R2)

- disallow 0, have 1 return the current element forward, -1 the current 
element backward

- allow 0, have 1 return the next element forward, 0 return the element 
before that


All have their advantages and disadvantages. All require explaining 
and may not be obvious depending on what you expect.

Yes, but that's not how my brain see it by default, I need to make 
a conscious effort for that. Also, I might be tempted to then use 
0 to access the first item instead of 1...This is a pitfall where 
almost every new (and maybe some older too) will fall in.

Yes, but don't try to generalise from your brain to "most" or "new" 
users.

The only somewhat arguable generalisation is to "those who are well-used 
to R2's behaviour".

I know, but I must try to put myself in future Red users shoes to 
be able to make decisions.

I think for future Red users, R2's model is actually the worst choice.

If we do R2's behavior, make sure that PICKZ and POKEZ exist so I 
have something to use. They can call PICK and POKE internally. I 
need something that does computed indexes/offsets, and I can't afford 
to have a hole in the list (0 for R2), and I can't count on the port 
scheme supporting SKIP.

Just erroring out on index 0 is ann improvement.

Making "pick 1" and "pick -1" return the same element is an improvement.
R3's behaviour is an improvement.

R2's messy behaviour with a clean set of SKIP, PICKZ, POKEZ is an 
improvement.

If I'm not doing computed indices/offsets, or doing negative/0 offsets, 
or using using port scheme4s where PICK/POKE mean something different, 
then I don't use PICK/POKE at all.

and I can't afford to have a hole in the list

 Brian, could you give us some short code cases where this was a problem 
 for you? This would really help.

pick ser idx + off

Just erroring out on index 0 is ann improvement.

 That's my intention for Red until we get a consensus on a better 
 overall solution.

We won't get consensus on this.

We won't if we stick to only R2/R3 options. Fortunately, there are 
other ones, maybe we'll find more.

Sorry, I didn't mean off in the sense of false, I meant short for 
an offset. Any place where you have computed indexes can have a computation 
that turns out to be less than 1, especially if your base position 
is offset.

Error out and add PICKZ, POKEZ while at it. That would at least give 
us a base to work with.

The problem with keeping most of R2's behaviour much longer is that 
switching to something different will only get harder.

Agreed.

Remember, R3's behavior isn't done either. There's a standing consistency 
bug, for instance. If we come to a consensus, R3 is likely to adopt 
it too.

So if, for example, we were to switch to 0-based indices-as-offsets 
complemented with an ordinal! type, it's better to do this sooner 
rather than later.

BrianH: CC for this consistency bug?

http://issue.cc/r3/609

Thanks.

I wouldn't even mind if PICKZ/POKEZ were the actions and PICK/POKE 
were the native wrapper functions. Not as pretty for port scheme 
implementors though.

Brian: in `pick ser idx + off`, how often do you need `idx + off` 
to give you both positive and negative results from the same expression?

Usually, the number I'm passing to PICK or POKE is computed elsewhere. 
That was a one-line example for simplicity.

I would just like to know if it's an issue (the 0 gap) you hit once 
in your lifetime or if it's something people encounter from time 
ot time or even often (depending on the coding style).

(just curious)

We should write a short-list of possible options that would solve 
the whole issue and see if we can get a large consensus on one of 
them. Anyone kind enough to extract the different options we've discussed 
and put them somewhere online with the main pros/cons?

I use computed indexes for computed lookup lists, such as for precomputed 
intermediate results of computations, translation tables, etc. If 
the computation uses signed numbers, you have to do an offset base 
position to get the results from the positions less than 1. Having 
a hole slows down the computation because it has to be handled in 
mezzanine code. PICKZ/POKEZ would actually be better for most of 
these situations because the computations work better with 0-based 
numbers (modulus, for instance). It's pretty common in code that 
actually *needs* to use PICK/POKE on series.

I've found that aside from computed indexes, the only times I use 
PICK/POKE on series are for negative/0 indexes, or indexes greater 
than 10. For the rest the ordinal functions are faster.

Of course port schemes and datatypes actually need to implement PICK/POKE, 
but at least for datatypes the implementation is usually native so 
the hole is less expensive to implement.

It's pretty common in code that actually *needs* to use PICK/POKE 
on series.


That's the sticking point. We can categorise the uses for PICK/POKE:

(a) with large positive literals
(b) with literals -1, -2
(c) with computed indices and series in "head position"
(d) with computed indices and an offset series

More categories welcome.

Having a hole slows down the computation because it has to be handled 
in mezzanine code.


Have you ever had to actually write such "0 gap" workaround in your 
code, or is Carl the only one that had ever been bitten by this isssue?

I think it's more common to rewrite the code to something different, 
where possible, than to try and workaround the 0 gap.