leanprover-community / leanprover-community/lean
Nested names confuse the typechecker
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Description
def nat.foldl.fin.template {α : Type} : α := sorry
def nat.foldl.fin {α : Type} (f : α) : α := nat.foldl.fin.template
This works for me.
def nat.foldl.fin.template {α : Type} : α := sorry
def nat.foldl.fin {α : Type} : ∀ (f : α), α | f := nat.foldl.fin.template
This does not.
I am using Lean 3.42.
Reposted from here.
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
Reproduce the two nested-name definitions in Lean 3.42 and compare the typechecker behavior. Start by tracing how the typechecker handles the dependent function form and nested declarations; done means the discrepancy is resolved and covered by a regression test for both examples.
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