`ghc-lib` is a literal subset of GHC files: `ghc-lib-parser` that set of files sufficient to produce abstract syntax trees (~200 files), `ghc-lib` the remaining set of files enabling Core generation from parsed syntax trees (~300 of those) (more detail in the project README here https://github.com/digital-asset/ghc-lib/blob/master/README.md).

There is at this time, no attempt to provide any additional interface, "higher level" or otherwise, in these packages.

The key property of `ghc-lib-parser`/`ghc-lib` that makes them useful to tool developers (e.g. HLint) is that they can utilize the GHC API without being bound to a specific compiler version to do so.