Writing a platform · beginners · Zulip Chat Archive

Hi! New to Roc, was inspired to learn it by some of the SYCL talks :)
I come from Zig land, so I'm interested in jumping right in to writing a platform to understand the low level details! Is there a reference anywhere for the functions I need to provide to roc, and how to call the entrypoint?
I've had a look at some example code but I'd like to know where the "source of truth" is for all the function names etc.
Not averse to reading the source, if that's the answer ^-^

Zeljko Nesic (May 18 2024 at 00:23):

Luke Boswell (May 18 2024 at 05:45):

Luke Boswell (May 18 2024 at 05:47):

I've been down the rabbit hole a bit lately on platform dev. When I get a spare moment, I'd like to try and write up something to help others with this, so any questions you have are really helpful.

Silver (May 18 2024 at 07:11):

Silver (May 18 2024 at 07:13):

I'm struggling a bit with understanding all the roc syntax involved - there's provides which, in a platform file, seems to export functions using C names? but I'm not entirely sure how those names are computed, since there's a number and sometimes a _generic or _caller or something involved

Silver (May 18 2024 at 07:16):

there's also hosted files which seem to handle interfacing with functions exposed by the host implementation, but I'm not clear on how those interact with purity.
There doesn't seem to be much documentation on Roc's effect system so I'm not really sure how that works - there's Effect, but also Task, which wraps Effect? Though ofc both of those are defined by the platform so I guess it's just convention?

Luke Boswell (May 18 2024 at 07:31):

A lot of this is not documented because it is a WIP and there are some changes planned I think. Zulip is probably the best way to find this information out.

Luke Boswell (May 18 2024 at 07:31):

I'm currently doing some touristing in Milan before I get on a plane back to Aus, but happy to help where I can.

Luke Boswell (May 18 2024 at 07:33):

Luke Boswell (May 18 2024 at 07:34):

For example this is how we want to change the interface between roc apps and the host.

Luke Boswell (May 18 2024 at 07:34):

Silver (May 18 2024 at 08:39):

Silver (May 18 2024 at 08:58):

I've had a look at the compiler source code and I think I understand the generated function names a little better now, but I'm still not 100% clear on the difference between roc__thing_0_exposed and roc__thing_0_exposed_generic - why does the platform-switching example use the _generic variant, and when would you use the non-generic version?

Luke Boswell (May 18 2024 at 09:11):

Im not sure, I think it might have been testing two different APIs or a WIP thing.

Silver (May 18 2024 at 09:20):

Silver (May 18 2024 at 09:21):

How do I run roc glue? I'm not sure what arg to give it for GLUE_SPEC and it's not giving terribly helpful errors when I try to guess haha

Luke Boswell (May 18 2024 at 09:30):

Luke Boswell (May 18 2024 at 09:31):

The first argument is the path to a glue spec, the second is the dir path to generate files into, the last is the platform you want to generate for. I suggest starting with a super basic platform.

Luke Boswell (May 18 2024 at 09:32):

Luke Boswell (May 18 2024 at 09:33):

I find it useful to encode the types from the compiler into JSON and then I can pretty format in my editor and easily see what the data is.

Silver (May 18 2024 at 09:34):

hmm okay, I guess I need a clone of the compiler source code for that then? since the glue specs don't seem to be distributed with the nightlies

Silver (May 18 2024 at 09:34):

That's sort of annoying since I was hoping to integrate it into my Zig build process

Luke Boswell (May 18 2024 at 09:35):

Luke Boswell (May 18 2024 at 09:36):

Silver (May 18 2024 at 09:36):

Luke Boswell (May 18 2024 at 09:37):

Yeah thats probably best. If you are interested in helping with Zig glue please let me know.

Silver (May 18 2024 at 09:37):

I'd love to at some point, but I'll prolly focus on just learning the language first! ^-^

Luke Boswell (May 18 2024 at 09:38):

app [makeGlue] {
    pf: platform "https://github.com/lukewilliamboswell/roc/releases/download/test/olBfrjtI-HycorWJMxdy7Dl2pcbbBoJy4mnSrDtRrlI.tar.br",
    json: "https://github.com/lukewilliamboswell/roc-json/releases/download/0.7.0/xuaMzXRVG_SEhOFZucS3iBozlRdObWsfKaYZMHVE_q0.tar.br",
}

import pf.Types exposing [Types]
import pf.File exposing [File]
import json.Core exposing [json]

makeGlue : List Types -> Result (List File) Str
makeGlue = \typesByArch ->
    typesByArch
    |> List.map convertTypesToFile
    |> List.concat staticFiles
    |> Ok

staticFiles : List File
staticFiles = []

convertTypesToFile : Types -> File
convertTypesToFile = \types ->

    content =
        Encode.toBytes types json
        |> Str.fromUtf8
        |> Result.withDefault "INVALID UTF8 ENCODED FROM JSON"

    { name: "types.json", content }

Luke Boswell (May 18 2024 at 09:39):

Im just on my phone, but that's using a URL package of glue I have been using for testing things.

Silver (May 18 2024 at 09:39):

Luke Boswell (May 18 2024 at 09:40):

Because glue spec is an app that is just a plugin for the compiler there are only .roc source files in the package and no prebuilt binaries.

Luke Boswell (May 18 2024 at 09:45):

Also if anyone is interested you can make your own bundle for glue package using something like roc build --bundle .tar.gz crates/glue/platform/main.roc and upload that somewhere.

Silver (May 18 2024 at 10:56):

Silver (May 18 2024 at 10:57):

Silver (May 18 2024 at 11:44):

In the platform header, what's the first {} in requires {} { main : Whatever }? I've only ever seen it empty so I'm intrigued as to what might go in it :)

Luke Boswell (May 18 2024 at 11:47):

Silver (May 18 2024 at 11:47):

Luke Boswell (May 18 2024 at 11:48):

Silver (May 18 2024 at 11:48):

Silver (May 18 2024 at 11:50):

Silver (May 18 2024 at 11:51):

Or reflection in the platform would work too I guess, if I could generate data to pass to the host

Silver (May 18 2024 at 11:52):

Luke Boswell (May 18 2024 at 11:59):

No reflection. I don't think its possible for the host to know beforehand as it's compiled separately from the app.

Silver (May 18 2024 at 12:00):

Apurva Mishra (May 18 2024 at 14:48):