How to Collect Type Errors?

Hello all, I want to write a plugin for Haskell Language Server, to collect type errors in the code. I'm new to GHC API, so I need some help. My current thought is, I can collect diagnostics or the error messages and extract the type error infos. I have tried to referred to the Haddock documentation for GHC API, but I'm still not sure which function should I use. Thanks, Guanda