Stream: contributing

Topic: ambient functions don't unify

view this post on Zulip Johan Lindskogen (Dec 07 2023 at 18:43):

Hi, while working on this issue: 6208 I bumped into some weird unification error and don't know what to try next.

I found the ROC_PRINT_MISMATCHES debug flag and the mismatch is Num.FloatingPoint.

Here are my changes so far: https://github.com/lindskogen/roc/commit/aa194419ac6160caf40710cee76e67a820c82430

ROC_PRINT_MISMATCHES=1 cargo run dev examples/cli/echo.roc
    Finished dev [unoptimized + debuginfo] target(s) in 0.27s
     Running `target/debug/roc dev examples/cli/echo.roc`
Mismatch in crates/compiler/unify/src/unify.rs Line 978 Column 17
`Num.FloatingPoint`

An internal compiler expectation was broken.
This is definitely a compiler bug.
Please file an issue here: https://github.com/roc-lang/roc/issues/new/choose
thread '<unnamed>' panicked at 'ambient functions don't unify', /Users/johan/Projects/roc/crates/compiler/unify/src/unify.rs:201:18
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

view this post on Zulip Brendan Hansknecht (Dec 07 2023 at 18:50):

Hmm, probably some code says that those only support float and adding Dec as an option is confusing it.

view this post on Zulip Brendan Hansknecht (Dec 07 2023 at 18:50):

I know I've seen this before, but it's been so long

view this post on Zulip Johan Lindskogen (Dec 07 2023 at 18:58):

Found a couple of issues in my code, where I didn't define DEC_SQRT & DEC_POW, but the issue stays the same :oh_no: https://github.com/roc-lang/roc/compare/main...lindskogen:roc:implement-sqrt-pow-for-dec

view this post on Zulip Brendan Hansknecht (Dec 08 2023 at 04:06):

I'll try to take a look at this tomorrow. That said, @Ayaz Hafiz any immediate ideas?

view this post on Zulip Ayaz Hafiz (Dec 08 2023 at 13:56):

Possibly the call to Inspect.toStr v? That seems like maybe a type mismatch?

view this post on Zulip Ayaz Hafiz (Dec 08 2023 at 13:56):

Does it work if you do Num.toStr v in your sample app instead

view this post on Zulip Brendan Hansknecht (Dec 08 2023 at 15:29):

Inspect.toStr should have the same type (once made concrete) as Num.toStr, but autoderive or something could totally be bugged.

view this post on Zulip Johan Lindskogen (Dec 08 2023 at 16:51):

When I try Num.toStr instead I get this:

Mismatch in crates/compiler/unify/src/unify.rs Line 1088 Column 17
Cannot unify structure TagUnion(UnionLabels { length: 2, labels_start: 10, values_start: 243, _marker: PhantomData<roc_module::ident::TagName> }, Any(125)) with opaque `Num.Num`

Last updated: Jul 26 2025 at 12:14 UTC