How to exploit ./hadrian/ghci to find errors quickly?

My recommendation: ./hadrian/ghci.

Richard, this suggestion has been so useful that I would like to follow it up. I'm about to change a type definition. This change may wreak havoc in many parts of GHC, and this is exactly what I want: I'm looking for type-error messages that will tell me what code I need to fix. I do this work in emacs using `M-x compile` and `next-error`. The key property is that `next-error` requires just a couple of keystrokes (C-x `) and it makes Emacs take me to the relevant source-code location quickly. But telling `M-x compile` to run `./hadrian/build` is quite slow. Is there a way to leverage `./hadrian/ghci` for this workflow? Norman