It comes with the territory for a fast moving language with new extensions like -XDerivingVia[1] -XLinearTypes[2], more often than not backed by a publication where its interaction with other features is considered. Some extensions are purely syntactic and are quickly understood -XLambdaCase[3] -XBlockArguments[4] -XMultiWayIf[5]. The compiler will suggest missing extensions. There is enough to hs98 for a lifetime of study (see work of Graham Hutton[6] and Jeremy Gibbons[7])

[1] https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/deri...

[2] https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/line...

[3] https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/lamb...

[4] https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/bloc...

[5] https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/mult...

[6] https://twitter.com/haskellhutt

[7] https://twitter.com/jer_gib