leanprover-community / leanprover-community/mathlib4
parsing error with `!`
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Description
import Mathlib.Data.Nat.Factorial.Basic
open Nat
example (n : ℕ) : ∃ m : ℕ, 0 + n ! = m := by
use n !
simp
The code above parses incorrectly. Replacing line 5 with use (n !) parses correctly.
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 by reproducing the Lean snippet from the issue and comparing the parse of use n ! with use (n !). Trace the parser entry point responsible for postfix notation and verify that the unparenthesized form parses correctly, then add a regression check for this example.
Written by the indexing model from the issue text.
Assessment
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100