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Hannes Mehnert 2024-05-16 11:46:39 +02:00
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Posts/Retreat2024
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@ -33,6 +33,8 @@ Talking about time - I don't think anyone wants to have two different sleep func
At the retreat we discussed and thought about replacing the functors in MirageOS with other mechanisms - conditional compilation (depending on the target) or the linking trick (dune variants) or a ppx are candidates, apart from other things (maybe first-class modules fit the requirement as well).
Another benefit of conditional compilation and dune variants is editor support -- jumping to the definition of time (clock, etc.) now simply works because the compiler knows which code is used at runtime (in contrast to when a functor is used).
I got into coding a bit, and first looked into conditional compilation with the [`select`](https://dune.readthedocs.io/en/stable/reference/library-dependencies.html#alternative-dependencies) clauses from dune. They turned out to be not very flexible (you've to decide in the package what are all the options, and which one to take). I switched to [dune variants](https://dune.readthedocs.io/en/stable/variants.html#dune-variants), where the idea is that you provide a virtual interface, and only when compiling the executable you specify the implementation. This is great, since the mirage tool (at mirage configure time) can emit the dependencies. I went ahead and defunctorised the whole network stack - it was nice to see it is possible, but this is not easily upstreamable. There's as well at least [one issue](https://github.com/ocaml/dune/issues/10460) in the dune variant code, I'm sure it will get debugged and fixed once we decide that dune variants are the solution we want to try out.
The current result is a [mail to the development list](https://lists.xenproject.org/archives/html/mirageos-devel/2024-05/msg00002.html), and a [defunctorising time PR](https://github.com/mirage/mirage/pull/1529), as well as a [bootvar PR](https://github.com/mirage/mirage/pull/1533) (relying on other PRs).