experiment: track lowest upper bound and greatest lower bound potential errors #5678
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Contributor
crusso
reviewed
Nov 24, 2025
| Bool | ||
| because there is no way to satisfy subtyping | ||
| Bool <: T (for argument `x`) | ||
| `T` inferred to `Int` but incompatible with `()` |
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Where is the () coming from, the return type?
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the return type yes
crusso
reviewed
Nov 24, 2025
| [var Nat] | ||
| because there is no way to satisfy subtyping | ||
| [var Nat] <: [var T] (for argument `x`) | ||
| `T` inferred to `()` but incompatible with `Nat` |
Contributor
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Maybe not worth the complexity? |
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Joining two unrelated types (using
glborlub) is not an immediate error, just results inNonorAny.This can lead to loosing type information in errors, example:
Non <: T <: Anystarting pointNat <: T <: AnyglbwithNatAny <: T <: AnyglbwithText, we lost info aboutNatandTextNow,
lubwithFloatfails with an over-constrained error, but at this point we only know thatT := Anywhich is not helpful.This PR adds tracking of 'failed' glb/lub by checking whether their result the the appropriate extreme and adds this extra error info to the error message.
Here it would say
'T' inferred to 'Nat' but incompatible with 'Text'However, this PR is not that helpful in common cases where our current error handling is enough.
So I'm not sure if the extra complexity is worth it.