JRI98 (Dec 13 2023 at 15:22): JRI98 (Dec 13 2023 at 15:22):Hello. I am trying to build a program that reads lines from Stdin, changes them and writes to Stdout.
Right now it looks like
app "hello"
packages { pf: "https://github.com/roc-lang/basic-cli/releases/download/0.7.0/bkGby8jb0tmZYsy2hg1E_B2QrCgcSTxdUlHtETwm5m4.tar.br" }
imports [pf.Task.{ Task }, pf.Stdin, pf.Stdout, pf.Stderr]
provides [main] to pf
loop : Task {} I32
loop =
line <- Stdin.line |> Task.await
when line is
End ->
Stderr.line "EOF"
Input s ->
{} <- Stdout.line (inputToOutput s) |> Task.await
loop
inputToOutput : Str -> Str
inputToOutput = \input ->
input
main : Task {} I32
main = loop
Eventually the inputToOutput function will get more complex, but right now I'm hitting a compiler error:
thread 'main' panicked at 'Error in alias analysis: error in module ModName("UserApp"), function definition FuncName("\x12\x00\x00\x00\x02\x00\x00\x00\xb5\x94\rioj\xd2="), definition of value binding ValueId(3): could not find func in module ModName("UserApp") with name FuncName(")\x00\x00\x00\x04\x00\x00\x00\xb5\x94\rioj\xd2=")', crates/compiler/gen_llvm/src/llvm/build.rs:5713:19
This seems to be the same as https://github.com/roc-lang/roc/issues/5701. I tried changing the code to circumvent the compiler error, but got no luck. Any tips? :smile:
Brendan Hansknecht (Dec 13 2023 at 15:59):Try writing it with Task.loop
JRI98 (Dec 13 2023 at 16:13):Thank you so much :grinning_face_with_smiling_eyes:
For anyone reading, the working program looks like
app "hello"
packages { pf: "https://github.com/roc-lang/basic-cli/releases/download/0.7.0/bkGby8jb0tmZYsy2hg1E_B2QrCgcSTxdUlHtETwm5m4.tar.br" }
imports [pf.Task.{ Task }, pf.Stdin, pf.Stdout, pf.Stderr]
provides [main] to pf
loop : Task {} I32
loop =
Task.loop
{}
(\state ->
line <- Stdin.line |> Task.await
when line is
End ->
{} <- Stderr.line "EOF" |> Task.await
Task.ok (Done state)
Input s ->
{} <- Stdout.line (inputToOutput s) |> Task.await
Task.ok (Step state)
)
inputToOutput : Str -> Str
inputToOutput = \input ->
input
main : Task {} I32
main = loop
As a note, long term both should work just fine I'm pretty sure, but our underlying effect primitive is kinda naive currently. We have plans to switch out the implementation, and I think that would fix this.
Last updated: Jul 26 2025 at 12:14 UTC