Syntax match strange error
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- Lean
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Description
Prerequisites
- [X ] Check that your issue is not already filed:
https://github.com/leanprover/lean4/issues - [ X] Reduce the issue to a minimal, self-contained, reproducible test case.
Avoid dependencies to Mathlib or Batteries. - [ X] Test your test case against the latest nightly release, for example on
https://live.lean-lang.org/#project=lean-nightly
(You can also use the settings there to switch to “Lean nightly”)
Description
Pattern matching on syntax can lead to unexpected errors as in:
import Lean
open Lean Meta
def foo (t : Term) : Name :=
match t with -- Failed to infer binder type
| `($x:ident > 0) => .mkSimple <| x.getId.toString ++ "_pos"
| `($x:ident > $y:ident) => .mkSimple <| x.getId.toString ++ "_gt_" ++ y.getId.toString
| `($x:ident > $_) => x.getId
| _ => `Bas
Context
See variations on https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/Weird.20errors.20in.20quotation.20match
Steps to Reproduce
The above code is enough.
Expected behavior:
This definition should work
Actual behavior:
There is a “Failed to infer binder type” error on the match line.
Versions
4.27.0-rc1
Impact
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Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the self-contained foo definition in the issue and reproduce the error against Lean 4.27.0-rc1 and the latest nightly. Compare the quotation patterns in the match arms, then verify that the definition elaborates without “Failed to infer binder type” while preserving the expected Name results.
Written by the indexing model from the issue text.
Assessment
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 35/100