Matthew Phillips (Nov 30 2023 at 16:37): Matthew Phillips (Nov 30 2023 at 16:37):How do you build a hello world to compile to wasi?
Matthew Phillips (Nov 30 2023 at 16:38):I've compiled the wasm example but that requires a JS host.
Notification Bot (Nov 30 2023 at 16:57):2 messages were moved here from #beginners > syntax: whitespace vs comma for items by Brendan Hansknecht.
Brendan Hansknecht (Nov 30 2023 at 17:00):To my understanding, wasi would use something like a zig host that contains a main with a roc platform. I think we support it, but I have not messed with that pipeline in a long time.
In the worst case, you can just compile the roc code with --no-link and targeting wasm. Then have a platform built for wasi link against that.
Brendan Hansknecht (Nov 30 2023 at 17:04):As a clarifying note, all roc code is totally agnostic of that information. Whether it is for the browser or wasi roc will generate the exact same thing. It is up to some sort of host to deal with mapping browser/wasi primitives to roc io primitives.
Oskar Hahn (Nov 30 2023 at 17:04):I have played around with wasi some time ago. I did not go far, but the hello world example worked.
I pushed the code here: https://github.com/ostcar/roc-wasi-platform
It is its own platform, written in zig. Currently, it only knows the Task writeLine. My goal was to support all wasi functions. But I lost the motivation :)
Matthew Phillips (Nov 30 2023 at 17:05):ah ok, this is my confusion then
Matthew Phillips (Nov 30 2023 at 17:05):wasi requires a bunch of bindings. I wasn't sure if that was built-in to Roc or not
Matthew Phillips (Nov 30 2023 at 17:05):So it sounds like someone needs to build that via a runtime. And Oskar has started that. Very cool
Brendan Hansknecht (Nov 30 2023 at 17:06):Yeah, Roc has no io primitives and depends on a platform for them. More context here: roc-lang.org/platforms
Matthew Phillips (Nov 30 2023 at 17:08):@Oskar Hahn doesn't wasi expect a "wasi_snapshot_preview1" imported value from the host? I don't see that in your host.zig
Oskar Hahn (Nov 30 2023 at 17:08):It is very easy to build this in zig. Zig has build an abstraction layer around wasi, so you can use the normal zig functions.
For example, the writeLine Task is just:
export fn roc_fx_stdoutLine(str: *RocStr) void {
const stdout = io.getStdOut().writer();
stdout.print("{s}\n", .{str.*.asSlice()}) catch unreachable;
}
There is nothing wasi specific about it.
Brendan Hansknecht (Nov 30 2023 at 17:10):I wonder if we could just compile the rust basic cli for wasi?
Matthew Phillips (Nov 30 2023 at 17:10):ok, so I'm trying to understand how things are linked here.
Matthew Phillips (Nov 30 2023 at 17:10):Doesn't wasi have some sort of concept for logging? And if so, how does roc_fx_stdoutLine get linked to that?
Matthew Phillips (Nov 30 2023 at 17:11):I was expecting to see some sort of mapping from "wasi method" to the implementation method roc_fx_stdoutLine but i don't see any such thing.
Matthew Phillips (Nov 30 2023 at 17:13):I will of course pull down your project and try it out :)
Matthew Phillips (Nov 30 2023 at 17:20):It does indeed work! I'm going to play around with this some more.
Richard Feldman (Nov 30 2023 at 18:00):@Brian Carroll might have some more info on this!
Brian Carroll (Nov 30 2023 at 18:04):Well in terms of what to do, Oskar has covered it.
I think there's a misunderstanding about how the various layers fit together.
@Matthew Phillips you actually wouldn't see names of WASI methods at the source code level unless you looked inside libc implementation code or something.
Brian Carroll (Nov 30 2023 at 18:07):So in the Zig code above, stdout.print will compile to different things on different targets.
If you compile for Windows then there will be some Windows API call in there.
If you compile for a Unix system there will be syscalls like write or something.
And if you compile that same Zig code for WASI then it will compile to WASI's version of write. I can't remember what it's called.
Brian Carroll (Nov 30 2023 at 18:10):Roc has no concept of Windows syscalls or Linux syscalls or WASI syscalls.
Brian Carroll (Nov 30 2023 at 18:11):Those things are dealt with by the compiler of the host language.
Brian Carroll (Nov 30 2023 at 18:17):Also WASI does not directly have a concept of "logging" really. It's a POSIX-like system interface, so it has a concept of stdout, and it has a concept of writing to files, and you can use those for logging if you want.
Matthew Phillips (Nov 30 2023 at 18:20):Ah ok, so in this case there's no connection because WASI doesn't have a concept of logging
Matthew Phillips (Nov 30 2023 at 18:20):But it does have one of filesystem access presumably
Matthew Phillips (Nov 30 2023 at 18:21):So somehow there needs to a connection between the platform's "readFile" method and the WASI "readFile" method
Matthew Phillips (Nov 30 2023 at 18:21):The platform being the roc platform, i mean
Matthew Phillips (Nov 30 2023 at 18:22):Or wait
Brian Carroll (Nov 30 2023 at 18:22):Matthew Phillips said:
But it does have one of filesystem access presumably
Yes it has the same concepts as Unix or Linux has. It's an interface layer to the OS. It has the same concepts as any OS.
Matthew Phillips (Nov 30 2023 at 18:22):OK, maybe I get it now
Matthew Phillips (Nov 30 2023 at 18:23):So, in the host.zig you would call zig's "readFile" method, and that thing, under the hood, connects to WASI's readFile method
Brian Carroll (Nov 30 2023 at 18:23):yep
Matthew Phillips (Nov 30 2023 at 18:25):Ok, then as far as the connection between the Roc code and the host.zig, I see roc_fx_stdoutLine as a Zig method. I assume that this is some sort of method naming convention that causes the connection?
Brian Carroll (Nov 30 2023 at 18:25):yes, the roc_fx_ prefix
Matthew Phillips (Nov 30 2023 at 18:25):roc_ probably always in front, then fx_ because that's the exported module in the main.roc
Brian Carroll (Nov 30 2023 at 18:26):fx is short for "effects"
Matthew Phillips (Nov 30 2023 at 18:26):Oh, so roc_fx_ is always the name? It's not because this module happens to export something "as Fx"?
Matthew Phillips (Nov 30 2023 at 18:27):If I changed that to as Something then it doesn't because roc_something_
Matthew Phillips (Nov 30 2023 at 18:27):It expects to be an Effects
Brian Carroll (Nov 30 2023 at 18:27):Oh wow OK if we're digging in this deep I'd have to look it up, I dunno
Matthew Phillips (Nov 30 2023 at 18:27):Not important :)
Matthew Phillips (Nov 30 2023 at 18:27):I know enough to know what to do to add a new method, so this has been a lot of help, thanks!
Brendan Hansknecht (Nov 30 2023 at 18:35):Name comes from here: https://github.com/ostcar/roc-wasi-platform/blob/1796542883803f9a573e1b29f89d0348e1e4d617/src/Effect.roc#L14
Brendan Hansknecht (Nov 30 2023 at 18:35):Always prefixed with roc_fx_
Brendan Hansknecht (Nov 30 2023 at 18:37):as Fx from: https://github.com/ostcar/roc-wasi-platform/blob/1796542883803f9a573e1b29f89d0348e1e4d617/src/main.roc#L10
is used for other generation.
Matthew Phillips (Nov 30 2023 at 18:46):So you mean, the roc_fx_ prefix is defined somewhere in the Roc compiler and not in the platform's code, right?
Matthew Phillips (Nov 30 2023 at 18:50):Not important that I understand this part just yet :) I'm unblocked to experiment.
Brendan Hansknecht (Nov 30 2023 at 18:51):the
roc_fx_prefix is defined somewhere in the Roc compiler and not in the platform's code, right?
yep
Luke Boswell (Nov 30 2023 at 20:00):Oh neat @Oskar Hahn, I was thinking about starting one of these.
It would be awesome to write up a zig glue spec which would make zig platforms so much quicker to write.
Definitely an after AoC project I'm keen to look at.
Matthew Phillips (Nov 30 2023 at 20:02):AoC?
Luke Boswell (Nov 30 2023 at 20:03):Advent of Code
Brendan Hansknecht (Nov 30 2023 at 20:07):to write up a zig glue spec
I have been debating doing this for a long time. I think zig would be the easiest language to build a nice spec for. comptime will make a lot of it super easy. c++ would also be pretty easy, but probably messier than zig due to more complex templates and some other struggles. c you have to use macros and repeated imports or way more code gen to get all of the types and it is much more painful.
Matthew Phillips (Nov 30 2023 at 20:08):This would be really amazing :)
Brendan Hansknecht (Nov 30 2023 at 20:08):I have been debating doing this for a long time.
That said, my list of things to look at or work on is quite large rn.
Matthew Phillips (Nov 30 2023 at 20:09):If I understand, it would be a single implementation of the IO methods that you could then use in any platform, right?
Brendan Hansknecht (Nov 30 2023 at 20:09):the zig glue spec?
Matthew Phillips (Nov 30 2023 at 20:19):Yeah
Matthew Phillips (Nov 30 2023 at 20:20):Like, it would be nice if there was a library that implemented readFile, other IO methods, and then you could use that library in a platform that compiles to WASI, and in a platform that compiles to native, etc.
Matthew Phillips (Nov 30 2023 at 20:21):So that the platforms don't all have to implement those themselves.
Brendan Hansknecht (Nov 30 2023 at 20:26):So zig glue spec is different. It is about automatically generating zig code that interacts with roc. That way you don't need to know roc internal details to write a zig platform. Instead, that will all be automatically generated. For example, all the code here was auto generated by the rust glue: https://github.com/roc-lang/basic-webserver/tree/main/platform/src/glue
Brendan Hansknecht (Nov 30 2023 at 20:26):That said, someone could totally make a zig library for implementing a number of common primitives that would then be shared between many platforms (like readFile).
Brendan Hansknecht (Nov 30 2023 at 20:28):That said, it would be up to each platform as to whether or not they support a readFile primitive. It may make sense for a cli platform to have read file, but it probably doesn't make sense for frontend webpage platform.
Luke Boswell (Nov 30 2023 at 20:29):@Matthew Phillips you're going to love the Module Params design. I just added a link on https://github.com/lukewilliamboswell/roc-awesome It's a longer read, and I think Agus has just started on parts of it. But yeah, platform independent libraries will be great!
Matthew Phillips (Nov 30 2023 at 20:33):Brendan Hansknecht said:
That said, it would be up to each platform as to whether or not they support a readFile primitive. It may make sense for a cli platform to have read file, but it probably doesn't make sense for frontend webpage platform.
yep, agree!
Matthew Phillips (Nov 30 2023 at 20:45):Luke Boswell said:
Matthew Phillips you're going to love the Module Params design. I just added a link on https://github.com/lukewilliamboswell/roc-awesome It's a longer read, and I think Agus has just started on parts of it. But yeah, platform independent libraries will be great!
I don't know Roc well enough yet to fully get it, but in general this makes me very happy :) Going to pour over the proposal some more
Luke Boswell (Nov 30 2023 at 21:27):I think for platforms, they will just expose low level primitive IO like TCP/IP or Streams etc and then the package/library ecosystem takes thing from there. With all modules being platform independent by design, this makes it really easy to share things across platforms that have similar functionality. E.g. any platform that has TCP/IP can use Agu's roc-pg to work with PostgreSQL servers etc
Last updated: Jul 26 2025 at 12:14 UTC