Stream: show and tell

Topic: syntax evolution in Rocci Bird

Richard Feldman (Jun 08 2026 at 03:28):

I'm looking through rocci bird updates (to the new compiler), and wow...the gap between this original function and the new one is really dramatic!

Richard Feldman (Jun 08 2026 at 03:29):

original function:

startingPlants : Task (List Plant) []
startingPlants =
    List.range { start: At 0, end: At 14 }
    |> List.walk (Task.ok (List.withCapacity 20)) \task, i ->
        plant <- randomPlant (i * 12) |> Task.await
        current <- task |> Task.await

        current
        |> List.append plant
        |> Task.ok

Richard Feldman (Jun 08 2026 at 03:31):

new one:

starting_plants! : () => List(Plant)
starting_plants! = || {
    0.to(15).map!(|i| random_plant!(i * 12)).collect()
}

Richard Feldman (Jun 08 2026 at 03:37):

(related: I have now found a motivating use case for map! :joy:)

Richard Feldman (Jun 08 2026 at 03:39):

also this will be faster at runtime because it's not instantiating a list at runtime like the old one (since 0.to(15) returns an Iter, not a List) - not to mention no Task data structures

Luke Boswell (Jun 08 2026 at 03:43):

So much clearer too

Last updated: Jun 16 2026 at 16:19 UTC