Nick Hallstrom (Feb 13 2023 at 05:41): Nick Hallstrom (Feb 13 2023 at 05:41):Every once in a while I get an error like the one below. Usually they seem to be because I had a syntax error in my code and I can fix them by finding the syntax error. This is the first time I've been stumped on one of them and I'm wondering if someone can help explain what this error means and how it can hopefully help me figure out what's wrong with my code.
Please file an issue here: https://github.com/roc-lang/roc/issues/new/choose
thread '<unnamed>' panicked at 'no lambda set found for (`22.IdentId(21)`, [
InLayout(
39,
),
InLayout(
250,
),
]): LambdaSet {
set: [
( 22.21, [InLayout(39), InLayout(106)]),
( 22.24, [InLayout(20), InLayout(21)]),
( 22.26, [InLayout(1)]),
],
args: [
InLayout(
1,
),
],
ret: InLayout(
1,
),
representation: InLayout(
83,
),
full_layout: InLayout(
95,
),
}', crates/compiler/mono/src/layout.rs:1506:17
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Can't give justice to the error, but in general would advise running roc check before compiling your code. Not sure if it would find the issue in this case, but it tends to crash less and report more proper errors that can help fix code and syntax bugs.
Nick Hallstrom (Feb 13 2023 at 05:53):I think I found the issue. I get that error when I have when Str.toU16 a is but if I change it to when (Str.toU16 a) is then it goes away. Can you not have expressions between when and is? Also, interestingly, running roc check on the bad version gives me 0 errors and 0 warnings found in 352 ms.
Nick Hallstrom (Feb 13 2023 at 05:54):Wait, now it's not working. What the heck. It was just working after that change. This is a weird one...
Nick Hallstrom (Feb 13 2023 at 06:04):Ok, maybe it's actually when there is a recursive function call. Is that not allowed in Roc?
Nick Hallstrom (Feb 13 2023 at 06:07):Here's the function that seems to be generating the error:
setVal : U16, U16, U8 -> Task {} []
setVal = \value, address, pin ->
_ <- await (Pca9685.setPinOffTicks address pin value)
_ <- await (Stdout.line "How is this?")
a <- await Stdin.line
if a == "next" then
addressStr = Num.toStr address
pinStr = Num.toStr pin
valueStr = Num.toStr value
Stdout.line "Set address \(addressStr) and pin \(pinStr) to value: \(valueStr)"
else
when Str.toU16 a is
Ok v -> setVal v address pin
Err _ -> Task.succeed {}
But if I change that second to last line to Ok _ -> Task.succeed {} then it compiles just fine
Nick Hallstrom (Feb 13 2023 at 06:19):Yep, after doing more testing it seems to be that recursion causes this error. I get something similar from the following:
main : Task {} []
main = test
test =
a <- await Stdin.line
if a == "done" then Task.succeed {} else test
But if I change the recursive test call into Task.succeed {} it compiles just fine
Brian Carroll (Feb 13 2023 at 08:14):Recursive calls are most definitely allowed! In a functional language, recursion is the only way to express loops. This is a compiler bug.
I've seen this before in my work on virtual DOM. There was some work on these bugs a while ago but I don't know the current status. @Ayaz Hafiz might be able to offer some insight.
Ayaz Hafiz (Feb 13 2023 at 14:14):yeah stuff like this we’re actively trying to fix. I’ve been on a kick, but had to slow down for the past couple weeks for other priorities. I’ll diagnose this in the afternoon. Thanks for the report Nick!
Ayaz Hafiz (Feb 13 2023 at 23:45):Okay, this was a really challenging bug.. took me all day :woozy_face: but https://github.com/roc-lang/roc/pull/5028 should fix it
Nick Hallstrom (Feb 13 2023 at 23:50):Wooohoo! That was fast! Thanks so much for hopping on this right away Ayaz
Nick Hallstrom (Feb 14 2023 at 03:59):That fix worked Ayaz! I'm no longer getting the error I was before. I have a new one though. Anybody know what would be causing this guy?
thread 'main' panicked at 'Error in alias analysis: error in module ModName("UserApp"), function definition FuncName("\x04\x00\x00\x00\x18\x00\x00\x00j3\x1e\x91C\xfb\x16K"): expected type 'union { ((),), ((),) }', found type '()'', crates/compiler/gen_llvm/src/llvm/build.rs:4748:19
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
I definitely seen that plenty of times. assuming roc check doesn't give a solution, these can be annoying to debug. I think I often resort to commenting out code to try and figure out what caused the issue. Maybe someone else has better advice.
Nick Hallstrom (Feb 14 2023 at 04:11):Ya unfortunately roc check gives nothing. I’ll give that a try, thanks
Ayaz Hafiz (Feb 14 2023 at 04:44):Do you have a debug build of the compiler? If so could you try running roc with the env var ROC_CHECK_IR=1 set and let us know if there is any output?
Nick Hallstrom (Feb 14 2023 at 15:05):That gave the same error. So maybe I don’t have the debug build? How would I know? I built the compiler from source
Folkert de Vries (Feb 14 2023 at 15:06):try ROC_CHECK_MONO_IR
Folkert de Vries (Feb 14 2023 at 15:07):you'd need to build from source without passing --release to cargo
Folkert de Vries (Feb 14 2023 at 15:07):that is the default, so probably your build is good
Nick Hallstrom (Feb 14 2023 at 15:21):CFC3F0FE-2626-4642-84B5-90386CF6E7B9.jpg
Same thing. Am I doing this right?
Folkert de Vries (Feb 14 2023 at 15:22):hmm, maybe that printing only happens after alias analysis?
Folkert de Vries (Feb 14 2023 at 15:24):try it without --optimize?
Nick Hallstrom (Feb 14 2023 at 16:18):Same thing
2E9CE00A-BDFB-4D1B-9C17-A52DF0F096EB.jpg
Nick Hallstrom (Feb 14 2023 at 16:18):I think I’m starting to figure it out though. If I comment out one of the platform functions that I added it goes away, so I must have messed something up there
Brendan Hansknecht (Feb 14 2023 at 20:25):He has the custom low memory profile, so that probably blocks it. He would have to enable debug asserts in the profile and recompile
Nick Hallstrom (Feb 14 2023 at 20:45):How do I do that?
Brendan Hansknecht (Feb 14 2023 at 22:19):https://doc.rust-lang.org/cargo/reference/profiles.html#debug-assertions
Brendan Hansknecht (Feb 14 2023 at 22:20):I think you just add debug-assertions = true under the profile on cargo.toml. of course this will lead to a full recompile.
Brendan Hansknecht (Feb 14 2023 at 22:20):So will be really slow
Nick Hallstrom (Feb 14 2023 at 22:22):Ok, I've finally narrowed down the issue. This fails with the previously mentioned error:
main : Task {} []
main =
_ <- Task.await (Pca9685.setPinOffTicks 0x0040 1 500)
_ <- Task.attempt (Pca9685.setPrescale 0x0040 121)
Task.succeed {}
But if I comment out either of the lines with the Pca9685 call then it works, it just doesn't seem to like them both in the same file.
Suuupuer weird, any idea why that might be?
Ayaz Hafiz (Feb 14 2023 at 22:31):what do setPinOffTicks/setPrescale look like?
Ayaz Hafiz (Feb 14 2023 at 22:32):Could you try running with ROC_PRINT_IR_AFTER_SPECIALIZATION=1 and dump what you get out into a gist? that might help too
Nick Hallstrom (Feb 14 2023 at 23:45):Here's the code for those @Ayaz Hafiz
https://github.com/Billzabob/roc-clock/blob/main/src/Pca9685.roc#L18-L31
I'll add the debug-assertions to my Roc build and try that flag. Could be a bit though since it usually takes almost an hour to compile from scratch
Nick Hallstrom (Feb 15 2023 at 01:24):CBE7FB8F-1A19-4529-BD66-95C3DF8641FF.jpg
Nick Hallstrom (Feb 15 2023 at 01:24):Is this useful?
Nick Hallstrom (Feb 15 2023 at 01:31):Guessing this means something is messed up in my I2c module?
Ayaz Hafiz (Feb 15 2023 at 01:41):Yes, that’s super useful!! Nice, thanks!
Nick Hallstrom (Feb 15 2023 at 05:56):Not sure if this helps Ayaz, but I was able to finally figure out that it seemed to be caused by a call to Task.fromResult. I changed it from this:
# ...
bytes <- await (I2c.readBytes address 1)
Task.fromResult (List.get bytes 0)
To just doing this for now:
#...
bytes <- await (I2c.readBytes address 1)
when bytes is
[h, ..] -> h
_ -> 0
It's obviously not as good this way, but it gets me past this bug for now and hopefully gives you some more useful info.
Ayaz Hafiz (Feb 15 2023 at 06:01):Thanks Nick. I have a hypothesis for what this is, will try to validate it later in the week. Thanks for all for your help here and work through the compiler bugs!
Last updated: Jul 26 2025 at 12:14 UTC