Error Message Annotation Plugins for Haskell
summary
Proposes a custom-error plugin interface for GHC that detects emitted type errors and either annotates or replaces them at pretty-print time, implemented in-production inside Damlc with about 100 lines of compiler-facing code; plugins run opt-in, stackable, and can fetch blurbs, hide library internals (lens examples), or add Elm‑like hints. Claims: minimal GHC changes, full access to typechecker context during rewrite, and practical utility shown by working examples and a small implementation.
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chapters (8)
- 0:00Introduction
- 2:08Type error message goals
- 5:43Existing approaches limits
- 10:43GHC plugin interface
- 12:31Plugin implementation
- 15:22Plugin use cases
- 18:52Future directions
- 21:25Q&A
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