This post is to announce the first public release of a paper we wrote about modularizing GHC (PDF)
As you may know, I’ve been involved into several refactorings of GHC (adding some module hierarchy, ditching DynFlags, etc.). I have been asked a few times to write a document providing an overview of the design that we wanted to reach.
I dutily started to write this document more than two years ago. It started as a compilation of issues about the current design. However it was a bit difficult to state refactoring principles: for example, it seems obvious to me that
SDoc mustn’t be coupled with
DynFlags, but why? What’s the underlying principle?
Later I found out that I was in fact reinventing Domain-Driven Design (DDD). So I’ve started to reframe the paper as applying DDD principles to GHC. However the paper was put on hold, mostly because welcoming a baby sucked most of my time and energy to work on it.
A few weeks ago, we figured out with John (who had read the draft) that the paper could help a HSoC applicant: https://github.com/haskell-org/summer-of-haskell/issues/143 With the invaluable help of John and Jeff, we strove to make a first release of the paper in less than a week. We obviously failed to meet this deadline. But a few more weeks later, it’s finally there: “Modularizing GHC” paper (PDF) (in case you missed the link above)
It’s an odd paper because it’s a mix of:
- an audit report: a compilation of design issues, with some historical perspectives
- a proposal: a proposed design for GHC, based on DDD
- an experience report: our experience with refactoring GHC, and some method hints for doing it efficiently
- an exposition of DDD to a FP audience, using GHC as an example
Note that in the first draft I planned to also include mentions of Cabal. It was finally left out because it was a highway to despair, and the paper was already very long. We also only briefly mention Hadrian. Both could deserve their own paper of this kind.
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