@hackage / ghc-tcplugin-api

This library provides a streamlined monadic interface for writing GHC type-checking plugins.

Each stage in a type-checking plugin (initialisation, solving, rewriting, shutdown) has a corresponding monad, preventing operations that are only allowed in some stages to be used in the other stages. Operations that work across multiple stages are overloaded across monads using MTL-like typeclasses.

Some operations, like creating evidence for constraints or creating custom type error messages, are also simplified.

Please refer to the associated GitHub repository for example usage.