Stream: beginners

Topic: Reading Stdin until EOT?

Taylor Troesh (Sep 29 2023 at 00:27):

How would I read from Stdin until EOT? I'm trying to pipe input into a basic-cli app and it crashes.

thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', src/lib.rs:298:45
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5

This is my best attempt:

            loop : Str -> Task [Step Str, Done Str] never
            loop = \a -> Task.attempt Stdin.line \x -> when x is
                Ok b -> Task.succeed (Step (Str.concat a b))
                Err _ -> Task.succeed (Done a)
            stdin <- await (Task.loop "" loop)

Brendan Hansknecht (Sep 29 2023 at 00:38):

I think this is a case where we need to change how the stdin function works on the platform

Brendan Hansknecht (Sep 29 2023 at 00:38):

I think we currently have it just unwrap the stdin option when it really should return an option in the function

Brendan Hansknecht (Sep 29 2023 at 00:38):

That way you know when you hit eof instead of crashing

Brendan Hansknecht (Sep 29 2023 at 00:39):

Basically, we have a bad default currently that crashes on any error and eof is being considered an error.

Brendan Hansknecht (Sep 29 2023 at 00:39):

This would probably be a good first issue for anyone interested.

Anton (Sep 29 2023 at 08:57):

Should we change the type of Stdin.line to Task [Input Str, End] *?

Isaac Van Doren (Oct 30 2023 at 00:52):

Should we change the type of Stdin.line to Task [Input Str, End] *?

I like the sound of that

Brendan Hansknecht (Oct 30 2023 at 01:20):

Should Eof be a normal state or an error state? I would assume it is a error that you normally match on/react to, but I guess either is valid

Brendan Hansknecht (Oct 30 2023 at 01:20):

Hmm...in rust, I guess it is result option str

Brendan Hansknecht (Oct 30 2023 at 01:21):

So eof is part of the positive side, not error side

Isaac Van Doren (Oct 30 2023 at 01:40):

Yeah I don't think it makes sense for eof to be considered an error

Isaac Van Doren (Oct 30 2023 at 03:24):

I have this implemented, just need to make sure everything is right and then I'll open up a PR another day

Last updated: Jul 26 2025 at 12:14 UTC