> On the bright side, GHC is written in Haskell, and this language is particularly well suited to performing massive refactorings with confidence that nothing breaks. Thus, it should be possible to refactor the GHC library towards a more robust and versatile design

and in fact Simon Peyton Jones continued by saying exactly that:

> You can do a heart or lung transplant on GHC and make truly major changes and the type checker just guides you to do all the right things. The difficult stuff is envisioning and being very clear about what you’re trying to do. Actually doing it is often not that hard.

So the two texts and the two opinions are completely in alignment. GHC is famously bad insofar as it has a poor design. But once a better design is designed, you can give it the heart transplant it needs without excess stress.

I have no idea how the heart transplant proposed by Sylvain Henry, John Ericson and Jeffrey M. Young is going. I suppose at some point there should be something checked in and a report about how painful or painless it was (and, potentially, if it's really completely wrong, perhaps a series of bug reports in the next seven releases of GHC).