Alex Nuttall (Feb 17 2024 at 18:52): Alex Nuttall (Feb 17 2024 at 18:52):I'm trying to do game of life in roc-wasm4 and I don't undestand how to get started in drawing something using List.walk.
update : Model -> Task Model []
update = \prev ->
model = { prev & frameCount: prev.frameCount + 1 }
{} <- W4.text (model.frameCount |> Num.toStr) { x: 32, y: 12 } |> Task.await
{} <- (
List.walkWithIndex model.grid (Task.ok {}) \task, row, y ->
# {} <- task |> Task.await
W4.rect {
height: 4,
width: 4,
x: 7 * 4,
y: (y |> Num.toI32) * 4,
}
)
|> Task.await
Task.ok model
the result:
Screenshot-2024-02-17-at-18.35.38.png
If I uncommented {} <- task |> Task.await I would expect to get a vertical line, but instead the command line just hangs.
Can anyone tell me what I'm doing wrong?
Anton (Feb 17 2024 at 19:07):Hi @Alex Nuttall :)
Can you share the full code?
Alex Nuttall (Feb 17 2024 at 19:10):Hi Anton
app "game_of_life"
packages {
w4: "../platform/main.roc",
}
imports [
w4.Task.{ Task },
w4.W4,
]
provides [main, Model] to w4
Program : {
init : Task Model [],
update : Model -> Task Model [],
}
Grid : List (List Bool)
Model : {
frameCount : U64,
grid : Grid,
}
gridSize = 40
white = Color1
blue = Color4
setColorPalette : Task {} []
setColorPalette =
W4.setPalette {
color1: 0xfbf7f3,
color2: 0xe5b083,
color3: 0x426e5d,
color4: 0x20283d,
}
main : Program
main = { init, update }
init : Task Model []
init =
{} <- setColorPalette |> Task.await
Task.ok {
frameCount: 0,
grid: List.repeat Bool.false gridSize
|> List.repeat gridSize
|> List.set
20
(
List.join [
List.repeat Bool.false 20,
[Bool.true],
List.repeat Bool.false 19,
]
),
}
update : Model -> Task Model []
update = \prev ->
model = { prev & frameCount: prev.frameCount + 1 }
{} <- W4.text (model.frameCount |> Num.toStr) { x: 32, y: 12 } |> Task.await
{} <- (
List.walkWithIndex model.grid (Task.ok {}) \task, row, y ->
# {} <- task |> Task.await
W4.rect {
height: 4,
width: 4,
x: 7 * 4,
y: (y |> Num.toI32) * 4,
}
)
|> Task.await
Task.ok model
and I'm running zig build -Dapp=examples/game-of-life.roc run
Brendan Hansknecht (Feb 17 2024 at 19:10):That looks correct at first glance. Might be hitting a roc bug. Yeah, full code as anton said, would be really helpful.
Worst case, to work around the bug, you probably need to pull that into a sub function and use Task.loop
Alex Nuttall (Feb 17 2024 at 19:37):Just extracting the List.walk part into a function resolves it, thanks!
drawGrid = \grid ->
List.walkWithIndex grid (Task.ok {}) \task, row, y ->
{} <- task |> Task.await
W4.rect {
height: 4,
width: 4,
x: 7 * 4,
y: (y |> Num.toI32) * 4,
}
update : Model -> Task Model []
update = \prev ->
model = { prev & frameCount: prev.frameCount + 1 }
{} <- W4.text (model.frameCount |> Num.toStr) { x: 32, y: 12 } |> Task.await
{} <- drawGrid model.grid |> Task.await
Task.ok model
Screenshot-2024-02-17-at-19.36.55.png
Last updated: Jul 26 2025 at 12:14 UTC