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

Norman Ramsey nr at
Fri Jan 28 16:52:00 UTC 2022

 > 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?


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