"Modularizing GHC" paper

[Benjamin Redelings]

This is a great paper!  The explanation of how DynFlags has wormed its 
way into more and more functions is quite interesting. I wonder if, in 
general, some developers lean away from refactoring and more towards 
"getting things done", whereas other developers lean into code 
refactoring and decreasing technical debt.

A few comments:

On page 2, the first sentence about design patterns derived from OO 
literature seems a little awkward.

On page 7, the phrase "code smell" could maybe be replaced.  In my 
experience the phrase "code smell" is often used to avoid explaining why 
an anti-pattern is actually problematic.  It is also a neologism, and is 
only used once in the paper.

On page 30, the explanation of DDD talks about "business rules", 
"business knowledge", "business software", "business situation", 
"business code", etc. was unfamiliar to me.  It seems to use the word 
"business" to talk about the specific goal of the code.  This seems to 
be using language specific to corporations to talk about the .  The 
usage of "business" in this way is limited to pages 30, 31, and 34.

On page 34, I didn't find the relationship between Figure 1 and Figure 2 
entirely clear.  It sounds like Figure 1 is the way things are, and 
Figure 2 is the way that things should be?  Maybe that could be made 
clearer in the figure captions.  Also, it seems like the main difference 
in the figures is that Figure 2 replaces mutual dependency between the 
boxes on the right (i.e. "Type checker, renamer") and the output 
languages ("Haskell", "Core") with mutual dependencies between the 
output languages... is that good, and if so, why?

On page 37, its unclear to me what A and B are.

Other than that, I found the paper really easy to read!  I personally 
found the purpose of disentangling different parts of the compiler 
intuitively clear -- modularity and separation of concerns seem like an 
obvious goal.  The quoted text on the topic of "supple design" seems 
very motivating!

-BenRI

On 5/4/22 6:42 AM, Sylvain Henry wrote:
> Hi GHC devs,
>
> With John Ericson and Jeffrey Young we wrote a paper about the 
> modularization of GHC. It gives a global picture for the refactorings 
> we have been performing (c.f. e.g. #17957) and some potential future 
> ones.
>
> Announce blog post: 
> https://hsyl20.fr/home/posts/2022-05-03-modularizing-ghc-paper.html
> Paper: https://hsyl20.fr/home/files/papers/2022-ghc-modularity.pdf
> Discussion on Reddit: 
> https://www.reddit.com/r/haskell/comments/uhdu4l/modularizing_ghc_paper/
>
> We welcome any feedback, here or on reddit.
>
> Cheers,
> Sylvain
>
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