refactor: eliminate decreasing_by in Parser.lean in favour of structural recursion
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Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 42/100
- Issue type
- Refactor
- Clarity
- Mostly clear
- Activity status
- Stale
- Domain
- compilers
Research direction
Open Lck/Regex/Parser.lean and inspect the parsing code at lines 646 and 912, then read the termination guidance in CLAUDE.md. Determine whether the affected recursive calls can use structurally smaller token lists; done means both uses of decreasing_by are removed, or an explanatory comment documents why restructuring is infeasible.
Written by the indexing model from the issue text.
Description
Problem
Lck/Regex/Parser.lean at lines 646 and 912 uses decreasing_by to convince the termination checker. Per CLAUDE.md, decreasing_by is a code smell for parsers — a well-structured LL(1) parser over a token list should terminate structurally.
Expected fix
Restructure the affected parsing functions so that recursive calls are made on a syntactically smaller token list, allowing the Lean termination checker to accept them without decreasing_by. If this turns out to be infeasible, document why with a comment.
References
- Observed by AI code review on PR #9
- See CLAUDE.md termination discipline
- Dominant language
- Lean
- Stars
- 2
- Forks
- 1
- PR merge metrics
- No merged PRs in 30d
Contributor guide
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- Open a pull request that references the issue number.
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oxc-project/oxc#26944 ·