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1 point by Pauan 4928 days ago | link | parent

"In tables, (foo 0 1) already means the same thing as (or foo.0 1). But hmm, maybe you're not interested in slicing tables. That's fine, then. ^_^"

What would a table slice even mean? They're not even ordered. The closest thing would be a table that has a subset of the keys of another table, but that wouldn't use numeric indexing.

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"The other issue was that I think at some point you were using (foo 0) to mean a one-element slice, and that would definitely be ambiguous with regular old indexing."

I was? (foo 0) should always be an element, not a slice. Ah well, it doesn't matter. If I did use that, I was incorrect.

I'll note that (del (foo 0)) is equivalent to (= (foo 0 1) nil) so perhaps that confused you.

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"Arc's 'cut accepts start and stop positions, and your slicing examples instead use a start position and a length."

They did? I always thought of it as being a start/end position, like cut. So for instance:

  (= foo '(1 2 3 4 5 6))

  (= (foo 2 5) nil)

  foo -> (1 2 6)
The way I'm doing it is, the number of elements is the end minus the start, so for instance, in the example above, 5 - 2 is 3, so it removed 3 elements, starting at position 2. This is exactly how cut behaves:

  (= foo '(1 2 3 4 5 6))

  (cut foo 2 5) -> (3 4 5)
In fact, I think it'd be a good idea for lists/strings in functional position to just delegate to cut, so (foo 2 5) would be the same as (cut foo 2 5)


2 points by rocketnia 4928 days ago | link

"What would a table slice even mean ?"

Hence my "but hmm." ^_^

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"I'll note that (del (foo 0)) is equivalent to (= (foo 0 1) nil) so perhaps that confused you."

Yeah, that's probably it.

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"I always thought of it as being a start/end position, like cut."

It's hard to tell because you use 0 as the start pretty often, but here are the two examples I was going off of:

From http://arclanguage.org/item?id=14656:

  (= foo '(1 2 3 4 5 6 7))

  (del (foo 1 4)) -> (1 6 7)
From http://arclanguage.org/item?id=14660:

  (= foo '(1 2 3 4))

  (del (foo 1 2)) -> (1 4)
Guess those were buggy. Well, now I know. :-p

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1 point by Pauan 4928 days ago | link

"Guess those were buggy. Well, now I know. :-p"

Ah, yeah, I switched from inclusive to half-open. And since I just so happened to use 1 as the start index, you couldn't really tell.

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1 point by akkartik 4928 days ago | link

What would a table slice even mean?

A sub-table with just the given keys?

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1 point by Pauan 4928 days ago | link

Well, sure, but you wouldn't use numeric indices to refer to that. :P It might be something like this:

  (subset x 'foo 'bar 'qux)
As opposed to:

  (x 0 1)
Which would be slice notation, which would work only on ordered sequences, like lists.

Which isn't to say that table subsets would be a bad idea, just that it's a different idea from list slicing, so there shouldn't be any ambiguities with slice notation (which was one of rocketnia's concerns).

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1 point by akkartik 4928 days ago | link

You could implement subsetting at function position, in which case it would be ambiguous. I already use :default in wart, so I don't care too much about that :) But yeah I hadn't thought of how to create ranges of keys. This may not be a good idea. You can't distinguish table lookup from a subset table with just one key/val, for example.

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1 point by Pauan 4928 days ago | link

Well, we could define it so table slicing would only happen with 3 or more arguments:

  (foo 'a 'b 'c)
...but I would consider that to be confusing, and would suggest an explicit function like "slice" or "subset".

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