Optional parameters make nested inductives fail to elaborate
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bug
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Description
Description
If a nested inductive goes through a type that has an optional parameter, there is an "application type mismatch" failure from the inductive command.
Steps to Reproduce
inductive A (α : Type)
| mk (x : Option α := none)
inductive B where
| node (children : A B)
Expected behavior: No errors
Actual behavior:
application type mismatch
optParam _nested.Option_2 none
argument has type
Option B
but function has type
_nested.Option_2 → Type
Versions
Lean 4.11.0 nightly from 7/22/2024
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 by reproducing the nested inductive example with the reported Lean 4.11.0 nightly version, then trace the inductive elaboration path where the optional parameter is applied. Done means the example elaborates without an application type mismatch and the behavior is covered by a regression test.
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