Crashed with Malformed Suffix

[fwgreen]

app [main] {
    pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.10.0/vNe6s9hWzoTZtFmNkvEICPErI9ptji_ySjicO6CkucY.tar.br",
}

import pf.Stdout
import pf.Task
import pf.Utc

Option a : [Some a, None]

main =
    start = Utc.toMillisSinceEpoch Utc.now! 

    list = List.range { start: At 0i64, end: At 1_000_000i64 }

    results = List.map list \i -> binarySearch list i

    dbg List.len results

    dbg (Utc.toMillisSinceEpoch Utc.now!) - start

    Stdout.line! "Done"

binarySearch : List I64, I64 -> Option I64 
binarySearch = \list, value ->
    find : I64, I64 -> Option I64
    find = \lowerBound, upperBound ->
        if lowerBound < upperBound then 
            None 
        else
            midPoint = (upperBound + lowerBound) // 2
            when List.get list (Num.toU64 midPoint) is 
                Ok x ->
                    when Num.compare x value is
                        LT -> find lowerBound (midPoint - 1)
                        GT -> find (midPoint + 1) upperBound
                        EQ -> Some midPoint
                _ -> None

    find 0 (Num.toI64 (List.len list) - 1)

── UNUSED DEFINITION in main.roc ───────────────────────────────────────────────

binarySearch is not used anywhere in your code.

27│  binarySearch = \list, value ->
     ^^^^^^^^^^^^

If you didn't intend on using binarySearch then remove it so future
readers of your code don't wonder why it is there.

── UNUSED IMPORT in main.roc ───────────────────────────────────────────────────

Stdout is imported but not used.

6│  import pf.Stdout
    ^^^^^^^^^^^^^^^^

Since Stdout isn't used, you don't need to import it.

── UNUSED IMPORT in main.roc ───────────────────────────────────────────────────

Utc is imported but not used.

8│  import pf.Utc
    ^^^^^^^^^^^^^

Since Utc isn't used, you don't need to import it.

────────────────────────────────────────────────────────────────────────────────

0 errors and 3 warnings found in 254 ms
.

Running program…

────────────────────────────────────────────────────────────────────────────────
Roc crashed with:

        MalformedSuffixed(@309-585)

Here is the call stack that led to the crash:

        roc.panic
        app.main
        .mainForHost
        rust.main

Optimizations can make this list inaccurate! If it looks wrong, try running without `--optimize` and with `--linker=legacy`

roc nightly pre-release, built from commit d47a073634e on Tue Jun 25 09:12:30 UTC 2024 on macOs 14.5

[Anton-4]

Thanks for reporting this @fwgreen!

In case it may help, this is a workaround:

dbg List.len results

end = Utc.toMillisSinceEpoch Utc.now!

dbg end - start

[Anton-4]

Minimal reproduction for future debugging:

app [main] { pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.10.0/vNe6s9hWzoTZtFmNkvEICPErI9ptji_ySjicO6CkucY.tar.br" }

import pf.Stdout
import pf.Task
import pf.Utc

main =
    dbg Utc.now!

    Stdout.line! "Done"

[kdziamura]

The corresponding place in compiler:

https://github.com/roc-lang/roc/blob/7e609bfdbf37b51dd8ae576462a99b7ff404ca63/crates/compiler/can/src/suffixed.rs#L133-L137

It was probably done to not mess with control flow, but I can't say precisely. @lukewilliamboswell any insights? Should we add better logging here or make dbg work with the bang?

[lukewilliamboswell]

It's an error. Dbg shouldn't be used with a bang suffix.

We should improve the error message. I think we just left it as something basic like MalformedSuffix and haven't added any actual error reports yet.

[Anton-4]

Dbg shouldn't be used with a bang suffix.

Can you expand on that @lukewilliamboswell? It seems like we can make it work and I think it's a feature users would like to have.

[lukewilliamboswell]

I think I need to defer to @rtfeldman here. It may be possible to unwrap it, but I think it also may be a deliberate design choice.

For example

# this could in theory
main =
    dbg Utc.now!

    Stdout.line! "Done"

# unwrap to
main =
    Task.await Utc.now \answer -> 
        dbg answer

        Stdout.line! "Done"

But do we want this?

[kdziamura]

Yeah, as I mentioned, it leads to control flow change. I think it makes sense that dbg is expected to be transparent for control flow. But dbg with bang requires the change only to make dbg work.

Upd. However, the alternative is to introduce the await manually

[rtfeldman]

But do we want this?

I think we want it! 👍

[kdziamura]

Ok, I'll add the fix

[kdziamura]

@rtfeldman I'd assume expect shouldn't support bangs inside? My intuition is if you await something for expect, you intend to use it later. But maybe there are special cases?