jan kili (Feb 01 2022 at 08:18): jan kili (Feb 01 2022 at 08:18):I don't know if this counts as "the first Roc game", since all Roc is doing is adjusting the speed of the ball+paddle... but it works great!
https://github.com/JanCVanB/roc-bevies
Folkert de Vries (Feb 01 2022 at 08:21):oh very cool!
Folkert de Vries (Feb 01 2022 at 08:21):the platform should be able to accept an u16, I can check why that did not work later today
jan kili (Feb 01 2022 at 08:23):Thanks! This is my first original (not entirely copy-pasted) Rust code, so it's likely that I misunderstood roc_std's (and Bevy's) constraints.
Folkert de Vries (Feb 01 2022 at 21:48):so bevy does not work for me currently (linker problems), but looking at the LLVM IR I don't see why having the roc code (ultimately speedForHost) return an I16. What was the problem you ran into?
jan kili (Feb 01 2022 at 22:15):I was simply hacking naively until something worked, so this could all be incorrect: The equation it plugs into seems to expect an f32, and Rust told me that it couldn't autocast an i128 to an f32. Instead, it suggested that it could do so for an i16, so I went with that.
Folkert de Vries (Feb 01 2022 at 22:18):are there downsides to roc just giving you an f32?
jan kili (Feb 01 2022 at 22:28):No, that would be great! I was working under the assumption that the only types I could pass between Roc & Rust were the pub RocFoo things in roc_std/, so basically RocStr, RocDec, and RocResult.
Folkert de Vries (Feb 01 2022 at 22:28):oh, no
Folkert de Vries (Feb 01 2022 at 22:28):all the primitive types also work
Folkert de Vries (Feb 01 2022 at 22:28):so ints and floats
jan kili (Feb 01 2022 at 22:28):🤯
Folkert de Vries (Feb 01 2022 at 22:29):these map 1 to 1 (except Nat becomes usize)
jan kili (Feb 01 2022 at 22:29):Well that's wonderful.
Folkert de Vries (Feb 01 2022 at 22:29):and as I said elsewhere records/structs also work in a predictable but not always intuitive way
jan kili (Feb 01 2022 at 22:29):I think I skimmed the examples and only found RocStr used.
Folkert de Vries (Feb 01 2022 at 22:30):so far sending integers was boring
jan kili (Feb 01 2022 at 22:31):Me: "Passing ints & floats must be hard, somehow. Dec it is!"
Folkert de Vries (Feb 01 2022 at 22:33):we just happen to agree on what the bits mean for number types
Folkert de Vries (Feb 01 2022 at 22:33):for strings for instance that is not true, because we have the small string optimization
jan kili (Feb 01 2022 at 22:35):Therefore, my next steps for roc-bevies is to (a) simplify int passing and (b) expanding breakout to populate most constant values & primitive formulae with Int/Float/Str/function fields of a big Roc configuration record
jan kili (Feb 01 2022 at 22:37):I love the idea of Rust/Bevy handling all the heavy rendering logic, then asking its boss Roc "hey, what sprite should I use here, and how many points does the player get for this?"
Folkert de Vries (Feb 01 2022 at 22:43):yes! I think it gets really interesting if the roc app stores some state
jan kili (Feb 01 2022 at 22:45):How??
jan kili (Feb 01 2022 at 22:45):Monadically?
jan kili (Feb 01 2022 at 22:47):I'd love to hear an example :D
Folkert de Vries (Feb 01 2022 at 22:50):No, I think game logic could live in roc. This may be a bit contrived but
Model : { score : U64 }
Msg : [ ScoredPoint ]
update : Model, Msg -> Model
update = \model, msg ->
when msg is
ScoredPoint -> { score: model.score + 1 }
view : Model -> U64
view = .score
you'd also need init = { score: 0 }
Folkert de Vries (Feb 01 2022 at 22:51):then the platform can call init, and then update the model it has every time a game event happens (e.g. score is increased), and "render" the score when needed
Folkert de Vries (Feb 01 2022 at 22:52):does this make sense in practice? I don't really know, but it's possible
jan kili (Feb 01 2022 at 23:27):Yes! This update-state-on-event loop is common in games, and Bevy has a managed hyperscalable version of that pattern in its ECS architecture
jan kili (Feb 01 2022 at 23:37):I suppose that Roc could complement an ECS platform with its own additional state management layer, but I'm not sure why it would
jan kili (Feb 01 2022 at 23:39):If your app doesn't have a fixed timestep, that could be a fun pattern for discrete event simulations :)
jan kili (Feb 02 2022 at 03:46):On second thought, since Bevy claims to be modular, moving state management (data layer, ECS, whatever) into Roc could be quite fun
jan kili (Feb 02 2022 at 03:47):I'm pretty bummed that it looks like Roc can't define Bevy game nouns (entities are defined via Rust struct literals) or verbs (system functions reference entity types), only support them with primitive-passing functions. Is that accurate?
Matthias Devlamynck (Feb 02 2022 at 09:11):I guess you'd need to have your platform code create rust types (macro?) from roc types.
Matthias Devlamynck (Feb 02 2022 at 09:13):Mirroring bevy's systems API to expose it to Roc may prove to be difficult ^^'
Folkert de Vries (Feb 02 2022 at 12:12):actrually @Richard Feldman have you thought about this? I remember we discussed writing database plugins in Roc which would run into the same issues: you'd want the database to understand your specific roc data structure. As far as I know, you can only do that with additional code gen
Folkert de Vries (Feb 02 2022 at 12:12):e.g. for postgress extensions in rust you need to derive a bunch of things
Folkert de Vries (Feb 02 2022 at 12:12):and it generates a ton of C code
jan kili (Feb 02 2022 at 12:14)::nerd::memo:
Richard Feldman (Feb 02 2022 at 12:30):so what we'd talked about awhile ago (a year or so maybe?) was something along these lines:
.roc file and it outputs a serialized representation (exact format TBD) of all the types that would get sent to the host, in a format that includes all the necessary low-level information (e.g. struct field ordering would have already taken into account alignment and alphabetizing)we hadn't talked about it in the context of Rust macros needing to get involved, but one idea for a particularly fancy way that could potentially work: in your Rust host's build.rs, use :point_up: to generate .rs files from your Roc types, with the (un-annotated) structs and everything, then - still in build.rs - modify those files to add the annotations (e.g. find/replace struct Player { with #[derive(BevyStuff)]\nstruct Player {), and then let the build continue as normal.
Richard Feldman (Feb 02 2022 at 12:34):so assuming all the generator prerequisites were in place (they don't exist yet, of course!) the workflow would be:
build.rs stuff will take care of keeping the Rust types in sync with the Roc types, and adding any annotations Bevy needs, so you can also build your Rust project with cargo as normal and it will stay in syncof course there's some extra setup work involved to make that generation/substitution happen at the right time, but I don't think that's avoidable in the general case whenever the goal is to sync type definitions between two decoupled programming languages :big_smile:
Folkert de Vries (Feb 02 2022 at 12:36):Right, the challenge is then to make the whole rust/c/zig codegen bit hidden from the Roc user
Folkert de Vries (Feb 02 2022 at 12:37):for https://github.com/zombodb/pgx they do this with a custom cargo command
jan kili (Feb 02 2022 at 12:37):@Richard Feldman That sounds awesome! I had no idea Roc could get that powerful.
jan kili (Feb 02 2022 at 13:22):That codegen feature addition would enable replacing roc-bevies (dozens of subgenre-specific platforms) with roc-bevy (one general-purpose gamedev platform).
Lucas Rosa (Feb 02 2022 at 17:52):cool stuff!
jan kili (Feb 09 2022 at 05:09):@Folkert de Vries :smiley: https://github.com/JanCVanB/roc-bevies/commit/70fc0e
Last updated: Jul 26 2025 at 12:14 UTC