Stream: beginners

Topic: List.sortAsc / sortDesc docs

Alex Nuttall (Mar 02 2024 at 18:04):

The description in the docs:

Sorts a list in ascending order (lowest to highest), using a function which specifies a way to represent each element as a number.

makes me think of some other function which could be implemented in terms of List.sortWith

sortAscBy = \list, select ->
    List.sortWith list \a, b ->
        when (select a, select b) is
            (sA, sB) if sA < sB -> LT
            (sA, sB) if sA > sB -> GT
            _ -> EQ

expect
    actual =
        sortAscBy
            [
                (1, "a"),
                (3, "b"),
                (2, "c"),
            ]
            \(n, _) -> n

    actual
    == [(1, "a"), (2, "c"), (3, "b")]

rather than sortAsc itself which is not a higher order function. Is this a mistake?

Brendan Hansknecht (Mar 02 2024 at 18:14):

I assume the doc is wrong and it is just supposed to sort lists of numbers.

Brendan Hansknecht (Mar 02 2024 at 18:16):

That said, sortby could be useful. Also, maybe ascending/descending should be a tag instead of in the function name.

Brendan Hansknecht (Mar 02 2024 at 18:16):

(deleted)

Brendan Hansknecht (Mar 02 2024 at 18:17):

Anyway, suggestions and api updates are definitely welcome.

Brendan Hansknecht (Mar 02 2024 at 18:19):

Oh also, there was definitely discussion on adding a proper Orderable or similar feature to make this generic.

Brendan Hansknecht (Mar 02 2024 at 18:20):

#ideas > ordering/sorting ability I think

Anton (Mar 02 2024 at 18:30):

I'll fix the docs.

Alex Nuttall (Mar 02 2024 at 18:53):

I do think think sortWith is pretty verbose, and sortBy covers 90% of the cases where it's useful

Brendan Hansknecht (Mar 02 2024 at 19:33):

Only for numbers, until we have something like ord, sortby is pretty limited

Richard Feldman (Mar 02 2024 at 19:51):

yeah nothing is blocking Ord if anyone wants to work on it!

Richard Feldman (Mar 02 2024 at 19:52):

we've talked about the design in https://roc.zulipchat.com/#narrow/stream/304641-ideas/topic/ordering.2Fsorting.20ability

Brendan Hansknecht (Mar 02 2024 at 21:22):

Wasn't sure if it resolved to s single design or not... Agreed implementation being this?

# Sort.roc
Sort implements
    compare : a, a -> [LessThan, Equal, GreaterThan] where a implements Sort

Then need to add auto derive. Will not add it to string? But will add it to all numbers including floats?

Luke Boswell (Mar 04 2024 at 04:13):

I've just added an issue #6551 to track this.

Richard Feldman (Mar 04 2024 at 12:36):

Brendan Hansknecht said:

Will not add it to string? But will add it to all numbers including floats?

yeah, don't add it to Str - and then I think let's start out with not adding it to floats and see how it goes in practice

Richard Feldman (Mar 04 2024 at 12:37):

(Rust doesn't have it for floats, seems to be ok)

Richard Feldman (Mar 04 2024 at 12:37):

maybe we'll end up wanting it, but it's easier to add it later than to try to remove it later :big_smile:

Last updated: Jul 26 2025 at 12:14 UTC