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Merge pull request #1134 from AleoHQ/rfc-countdown-loops

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[RFC] Extend the countdown loops RFC.
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Alessandro Coglio 2021-07-13 12:57:38 -07:00 committed by GitHub
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docs/rfc/005-countdown-loops.md
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@ -17,7 +17,7 @@ DRAFT
# Summary
This proposal suggests adding countdown loops and inclusive loop ranges into Leo language.
This proposal suggests adding countdown loops and inclusive loop ranges into the Leo language.
# Motivation
@ -122,9 +122,36 @@ function shaker_sort(a: [u32; 10], const rounds: u32) -> [u32; 10] {
}
```
## Possible Future Extension
While the ability to designate the ending bound of a loop as either exclusive or inclusive is critical as discussed below,
we could also consider adding the ability to designate the starting bound of a loop as either exclusive or inclusive.
If we do that, we run into a sort of asymmetry in the defaults for starting and ending bounds:
the default for the starting bound is inclusive, while the default for ending bounds is exclusive.
The most symmetric but verbose approach is exemplified as follows:
* `0=..=5` for `0 1 2 3 4 5`
* `0<..=5` for `1 2 3 4 5`
* `0=..<5` for `0 1 2 3 4`
* `0<..<5` for `1 2 3 4`
* `5=..=0` for `5 4 3 2 1 0`
* `5>..=0` for `4 3 2 1 0`
* `5=..>0` for `5 4 3 2 1`
* `5>..>0` for `4 3 2 1`
That is, this approach makes exclusivensss an inclusiveness implicit.
The use of `<` vs. `>` also indicates a loop direction, which can be inferred anyhow when the `const` bounds are resolved,
so that would entail an additional consistency check,
namely that the inequality sign/signs is/are consistent with the inferred loop direction.
Within the symmetric approach above, there are different options for defaults.
The most symmetric default would be perhaps `=` for both bounds,
but that would be a different behavior from current Leo.
We could instead go for different defaults for starting and ending bounds,
i.e. `=` for the starting bound and `<` or `>` (depending on direction) for the ending bound.
# Drawbacks
-
No obvious drawback.
# Effect on Ecosystem