Luke Boswell (Oct 23 2024 at 01:13): Luke Boswell (Oct 23 2024 at 01:13):I'm just wondering if anyone would like to help with the work to upgrade to Purity Inference? My understanding is that Agus has made the changes backwards compatible, so this isn't an urgent or blocking thing, but helpful to find any issues.
I've been having fun working on it, and thought others might like to get involved too. I'm happy to help anyone if they would like to learn more.
I've started the upgrade for basic-cli here https://github.com/roc-lang/basic-cli/pull/257 and done all the platform/*.roc files. Next up would be upgrading the examples/*.roc files and getting those all happy with roc check.
Then we need to update the host roc_fx_* type signatures, and update the call from the host into roc (which is now so much simpler with purity inference).
I've completely upgraded roc-ray to purity inference, so we have that as an example if we need. You can see the code and test it out if you want here https://github.com/lukewilliamboswell/roc-ray/pull/38
Sam Mohr (Oct 23 2024 at 03:05):I'm your guy
Sam Mohr (Oct 23 2024 at 03:06):Do you have anything in particular that you already want to do, or is it just the stuff you listed?
Luke Boswell (Oct 23 2024 at 03:17):Yeah just the stuff I listed. :sunglasses:
Sam Mohr (Oct 23 2024 at 03:20):Sounds good. I probably won't have that much time for this, so we'd be happy to have any volunteers for this!
Oskar Hahn (Oct 23 2024 at 06:10):Could you list the things necessary to update a platform?
! and change -> to =>. How did the interface between the platform and the host change? You write, that roc_fx_* has to be updated. In which way?
Agus Zubiaga (Oct 23 2024 at 12:59):The main difference is that effects that can’t fail would return their values directly instead of being wrapped in Result, so you need to adjust the host to reflect that. If the effectful function returns {}, the host side would just be void. The name of the roc_fx_* function remains unchanged. The ! suffix that would appear in the hosted function is dropped.
Agus Zubiaga (Oct 23 2024 at 13:02):The other difference is that when you are running Task in the host today (from the entry point), you have to unwrap the closure inside and call that, but now you’d get effectful functions instead that you can run directly
Agus Zubiaga (Oct 23 2024 at 13:03):You can see these changes in Luke’s PR: https://github.com/lukewilliamboswell/roc-ray/pull/38/files#diff-fb36a3f95902a5f802b4bedd10bbe149ef6acb768f7815bf10f15ecbeb486595
Agus Zubiaga (Oct 23 2024 at 13:04):That’s it for the host side
Agus Zubiaga (Oct 23 2024 at 13:06):As Luke said, the compiler will be backwards compatible with Task for a while. It detects what fx mode to use based on whether the platform’s hosted module exposes effectful functions or Task.
Brendan Hansknecht (Oct 23 2024 at 15:10):As a note, the changes to the platform API are basically going back to before we had task as builtin. For example, I updated wasm4 from before task as builtin directly to purity inference. The host basically didn't change. The one caveat is that I stopped returning a record of lambdas to the host and instead returned two functions cause that is simply nicer to use from the host.
Oskar Hahn (Oct 23 2024 at 21:22):So is it possible now to export more than one function? That is nice.
Luke Boswell (Oct 23 2024 at 22:10):One thing I'd add is that purity inference hasn't landed in roc main yet. So the first thing I did was update the nix flake to point at the branch.
inputs = {
roc.url = "github:roc-lang/roc?ref=purity-inference";
nixpkgs.url = "github:nixos/nixpkgs";
};
Then I basically started updating the type annotations and just followed the compiler errors all the way through until I was completed (for the platform side). :smiley:
Brendan Hansknecht (Oct 23 2024 at 22:56):So is it possible now to export more than one function? That is nice.
yeah, this is in nightly currently. Don't even need purity inference for it. I added it a few weeks back
Brendan Hansknecht (Oct 23 2024 at 22:56):Makes a lot of apis a lot simpler in the platform. Anything to get away from dealing with closures
Brendan Hansknecht (Oct 24 2024 at 18:17):@Agus Zubiaga one thing to double check that came up in #compiler development > Early return and correct refcounting. We need to make sure that we don't reorder effectful function calls. I assume they all get toposorted with the pure functions currently. Unlike task where the await lambas enforced order, purity inference would have nothing to enforce order.
Brendan Hansknecht (Oct 24 2024 at 18:41):Yeah, just tested something really basic in roc-wasm4. This will reorder, which could be really problematic for side effecting ops:
i =
W4.trace! "this should print first"
j
j =
W4.trace! "this should print second"
1
outputs:
this should print second
this should print first
I think this, while being problematic, should still be outside of the purity inference PR
Sam Mohr (Oct 24 2024 at 18:44):We should make a separate PR that:
Sam Mohr (Oct 24 2024 at 18:49):By "efficiently feasible", I mean that even though errors saying "you defined y after x so you can't use y in x" would be helpful, I'm not sure if they require creation of a dependency graph, and I expect standard liveness checking would be a good bit more efficient
Richard Feldman (Oct 24 2024 at 18:52):I think we still need the same dependency graph to check for things like cyclic definitions
Richard Feldman (Oct 24 2024 at 18:52):we just need to not use it to reorder as many things as we are today
Agus Zubiaga (Oct 24 2024 at 18:53):Oh, great catch! I forgot we did this
Agus Zubiaga (Oct 24 2024 at 18:56):So we would reorder unless the def calls an effectful function, in which case we would report an error?
Agus Zubiaga (Oct 24 2024 at 18:56):Or do we want to always require that defs are defined in order unless recursive?
Agus Zubiaga (Oct 24 2024 at 18:57):(deleted)
Brendan Hansknecht (Oct 24 2024 at 18:59):Current plan is that everything is in order except for top level definitions.
Brendan Hansknecht (Oct 24 2024 at 19:00):Just makes the model simple
Agus Zubiaga (Oct 24 2024 at 19:01):Oh ok. Except top-level and recursive functions, right?
Richard Feldman (Oct 24 2024 at 19:01):I think we decided to disallow inline recursive functions
Agus Zubiaga (Oct 24 2024 at 19:01):I’ll read the other thread
Richard Feldman (Oct 24 2024 at 19:01):just be like if you need a recursive function, make it top-level
Richard Feldman (Oct 24 2024 at 19:01):comes up super rarely (if ever) anyway haha
Agus Zubiaga (Oct 24 2024 at 19:02):Ok yeah, that’s really simple :grinning:
Agus Zubiaga (Oct 24 2024 at 19:04):@Sam Mohr are you planning to work on this change or should I?
Sam Mohr (Oct 24 2024 at 19:06):I'm happy to work on it, but not planning on it
Sam Mohr (Oct 24 2024 at 19:06):If you've got time, feel free!
Sam Mohr (Oct 24 2024 at 19:07):If you don't pick it up, I'll do it once I finish return
Sam Mohr (Oct 24 2024 at 19:07):As you point out, it's easy for either of us to do :smile:
Agus Zubiaga (Oct 24 2024 at 19:08):Cool! Let’s just make sure we tell the other if we start it :big_smile:
Sam Mohr (Oct 24 2024 at 19:08):haha sure thing
Brendan Hansknecht (Oct 24 2024 at 19:39):just be like if you need a recursive function, make it top-level
I assume a self recursive function should work fine even if nested? It is just mutually recursive functions that will be blocked?
Richard Feldman (Oct 24 2024 at 19:41):right, yeah
jan kili (Nov 07 2024 at 16:09):I've been working with Luke to try to update roc-platform-template-rust, and I've been hitting confusing setup issues and lower-level-than-expected errors. Is that work the best way for a higher-level programmer like me to help purity-inference along, or is there another way I can help it get into main / usable?
Agus Zubiaga (Nov 07 2024 at 18:05):Can you post an example? Do you mean you found bugs in the code generation or confusing error messages?
Agus Zubiaga (Nov 07 2024 at 18:07):I know getting the memory layouts right on the platform side is tricky, but I think that’s orthogonal to purity inference itself
Agus Zubiaga (Nov 07 2024 at 18:12):Re getting on main, I’m planning to merge shortly but some tests seem to be failing on Linux despite the programs they run working fine outside of tests
Agus Zubiaga (Nov 07 2024 at 18:15):It seems to be related to building a platform multiple times in parallel. I tried to fix it by building it only once and then using —prebuilt-platform but that didn’t help. I’ll take another look tonight.
jan kili (Nov 07 2024 at 18:27):roc_std in roc_host/, which seems like a simple confusion that compounds everything else but also points to my general ignorance as to how packages are builtcargo build froze with no error message here: https://github.com/lukewilliamboswell/roc-platform-template-rust/pull/2#issue-2636489209 jan kili (Nov 07 2024 at 18:32):Stepping back a bit, I'm getting frustrated because I've been wanting to write a new Roc app by extending a basic platform, but I keep getting blocked by lower-level things like how platforms work behind the senes. It feels like we're in an in-between time where I shouldn't use main and I can't use purity-inference, but maybe I just need to start with main & basic-cli instead of a template?
jan kili (Nov 07 2024 at 18:34):Perhaps I've oversold my capacity to assist, since I'm only poking at this for like 30 minutes per day and don't feel like learning much that is tangential to my goals.
Agus Zubiaga (Nov 07 2024 at 18:36):Note that we don’t have to migrate platforms to get the purity inference PR merged since it’s backwards compatible with Task-based platforms.
Agus Zubiaga (Nov 07 2024 at 18:38):You can’t mix and match in an app, but we can incrementally migrate platforms after merging
Agus Zubiaga (Nov 07 2024 at 18:39):I don’t have a lot of free time now, so my focus is on getting the PR merged, but I’m happy to help with any platform efforts after
jan kili (Nov 07 2024 at 18:47):Sounds like maybe I should just use the nightly and build on basic-cli as-is!
Luke Boswell (Nov 07 2024 at 19:55):Agus Zubiaga said:
Re getting on main, I’m planning to merge shortly but some tests seem to be failing on Linux despite the programs they run working fine outside of tests
Can we please ignore them. We've done a big uplift in the rebuild host PR and we will merge them in once purity inference lands.
Agus Zubiaga (Nov 07 2024 at 20:12):Yeah, we could. It just occurred to me that I was testing the program on Linux arm while the tests run on x86. I’ll check that first just in case.
Jasper Woudenberg (Nov 07 2024 at 22:30):I'm trying out the purity inference branch with the Zig platform I'm working on. Really pleaseant experience so far, with great error messages.
I ran into a corner case. Suppose I have the following code:
foo : {} => U8
expect foo {} == 25
I get this warning:
── EFFECT IN TOP-LEVEL in platform/PagesInternal.roc ───────────────────────────
This call to PagesInternal.foo might produce an effect:
12│ expect foo {} == 25
^^^^^^
This is a weird example, in the real one that I simplified to this I have a higher-level function that supports running effectfully or not depending on the function passed in, and I have a couple of tests where I pass in pure functions. I don't think the warning should show under those circumstances (the test pass).
Also, I don't think code in an expect is considered top-level, right?
Sam Mohr (Nov 07 2024 at 22:34):To my understanding, we have avoided support for effect polymorphism, meaning that a function that takes in either a pure or effectful function will "assume" it takes an effectful function
Sam Mohr (Nov 07 2024 at 22:34):For us to support that would entail exposing fx variables in user code, which is messier than we want for now
Sam Mohr (Nov 07 2024 at 22:35):Though in the future we may realize we get strong benefit from effect polymorphism, so the door isn't fully closed
Sam Mohr (Nov 07 2024 at 22:35):All in all, I'd say this is expected behavior
Agus Zubiaga (Nov 07 2024 at 22:35):Yeah, if you managed to write an effect polymorphic function, I’d be really interested to see it because that’d be considered a bug :laughing:
Sam Mohr (Nov 07 2024 at 22:36):And yes, the expectat the top-level considers its body as part of the "top-level" code
Agus Zubiaga (Nov 07 2024 at 22:37):we probably need a specific error message for effects in expects
Agus Zubiaga (Nov 07 2024 at 22:37):“top-level” might be confusing in that context
Sam Mohr (Nov 07 2024 at 22:38):Eventually the plan is to remove expect-fx and just have expect \get!, set! -> ..., so we can probably improve the error messages then
Sam Mohr (Nov 07 2024 at 22:38):But it would be an improvement to add that now, too
Agus Zubiaga (Nov 07 2024 at 22:41):Yeah, that’ll come later
Sam Mohr (Nov 07 2024 at 22:42):"add that now" meaning the top-level expect with effects message
Agus Zubiaga (Nov 07 2024 at 22:48):Oh, I think I know where the confusion might come from. You are allowed to pass a pure function to something that expects an effectful function. However, the higher order function is still considered effectful.
Agus Zubiaga (Nov 07 2024 at 22:52):You get warnings for things that don’t make sense like discarding the result of a pure function because that’s dead code. But otherwise, pure unifies with effectful.
Agus Zubiaga (Nov 07 2024 at 22:53):and not the other way around, of course
Jasper Woudenberg (Nov 07 2024 at 22:54):Ah that makes sense, thanks.
I ran into something else. I've some functions that construct some build steps. Basically they take effectful functions and store them in a record without running them, and so are not effectul themselves (the compiler agrees). The record field needs a !, so far so good. However, in some places I'm initializing that record with a pure function and I get a warning
Config : {
fn! : U8 => U8,
}
init : Config
init = {
fn!: \x -> x,
}
── UNNECESSARY EXCLAMATION in platform/PagesInternal.roc ───────────────────────
This field's value is a pure function, but its name suggests
otherwise:
20│ fn!: \x -> x,
^^^^^^^^^^^^
I can't take out the ! as the error suggests, because that would break the contract and constrain fn to be effectful everywhere.
Jasper Woudenberg (Nov 07 2024 at 23:04):I managed to get rid of those earlier warnings I mentioned. I just had to manually created a pure version of the "polymorphic" function, use that version in tests, pull the common pure logic between the two (almost the entire function) into a helper. Pretty neat :heart_eyes:.
Agus Zubiaga (Nov 07 2024 at 23:56):Jasper Woudenberg said:
── UNNECESSARY EXCLAMATION in platform/PagesInternal.roc ─────────────────────── This field's value is a pure function, but its name suggests otherwise: 20│ fn!: \x -> x, ^^^^^^^^^^^^I can't take out the
!as the error suggests, because that would break the contract and constrainfnto be effectful everywhere.
Oh, that's a really good catch! I guess we only want this warning for record annotations, and destructuring, but not in record literals specifically.
Agus Zubiaga (Nov 08 2024 at 00:01):we do want the opposite (MISSING EXCLAMATION) for record literals
Luke Boswell (Nov 18 2024 at 04:55):I think I found another strange purity-inference related bug while upgrading roc-wasm4
https://github.com/lukewilliamboswell/roc-wasm4/pull/32#issuecomment-2481949480
I'm having trouble finding the source of this.
Luke Boswell (Nov 18 2024 at 04:55):$ roc build ./examples/sound.roc --target=wasm32 --no-link
thread 'main' panicked at crates/compiler/mono/src/reset_reuse.rs:1269:42:
Expected symbol to have a layout. It should have been inserted in the environment already.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
I see that all first-party platforms use pre-purity-inference Task-ful syntax. Do we/you want to intentionally defer all purity-inference update work until after AoC for stability and to prioritize responding to newcomer issues? Or do we/you hope to push basic-* across the finish line by next week?
Luke Boswell (Nov 21 2024 at 22:34):Just waiting on a review for https://github.com/roc-lang/roc/pull/7204
If we can merge that and get a new nightly... it's a clear path to a new purity-inference basic-cli
Luke Boswell (Nov 21 2024 at 22:36):So could be on the streets early next week... folks can always use an older Task-based version of basic-cli if there are any issues with the new purity inference one, so we can keep it in pre-release until it's had a few more people test it out
jan kili (Nov 21 2024 at 22:40):In all but the most optimistic forecasts, does that mean we should prepare to keep post-purity-inference first-party platforms in pre-release mode until after AoC?
jan kili (Nov 21 2024 at 22:43):If not, then the tutorial and documentation seem unready to assist newcomers with that, conceptually or snippetly. https://www.roc-lang.org/tutorial#tasks
jan kili (Nov 21 2024 at 22:50):Basically, I'm expecting someone to announce a month-long AoC freeze on breaking changes to @roc-lang, for UX.
Luke Boswell (Nov 21 2024 at 22:52):I'm hoping we can switch over to the release management process we've discuss/agreed on
Basically, we can make breaking changes to roc but the supported platforms and recommended version for everything stays stable/relibable.
Luke Boswell (Nov 22 2024 at 03:08):Does anyone want to have a crack at updating the Tutorial for purity inference? Not a major uplift, just removing Task
jan kili (Nov 22 2024 at 06:13):Shouldn't such an update also add explainers for !, =>, and try?
Luke Boswell (Nov 22 2024 at 06:20):Sounds like you're halfway there @JanCVanB :grinning_face_with_smiling_eyes:
jan kili (Nov 22 2024 at 06:22):Hehe but I still don't fully understand where Tasks went so I'm hesitant to explain anything!
jan kili (Nov 22 2024 at 06:23):(Side note, the tutorial and linked examples still use ?, which seems maybe deprecated/removed?)
jan kili (Nov 22 2024 at 06:26):I'm happy to give it a try tomorrow, partly as an exercise in outlining my own confusions!
jan kili (Nov 22 2024 at 06:28):With such inspiring sentences as "I infer that try bubbles any downstream Err tags up all the way to the platform, though you can no longer see the tags in function signature types... hmm that doesn't seem right..."
Edit: yay I'm wrong on the "no longer see" part
Luke Boswell (Nov 22 2024 at 06:28):Getting started is the hard part :smiley: I'm sure we can help to find the right words. It would be very helpful to sit back and think about the new things (syntax etc) and map out what is missing or needs adding.
I'm not thinking we should add/update everything, but we could do a pass or two and polish it a little so newcomers can still follow along and have a good experience.
jan kili (Nov 22 2024 at 06:35):As a returning user, I'm concerned that in the last month or two Roc has frontloaded its complexity (slightly steepened its learning curve to greatly improve code readability) without yet paying the cost in documentation or newcomer pushback... right before AoC.
Sam Mohr (Nov 22 2024 at 06:38):JanCVanB said:
Hehe but I still don't fully understand where Tasks went so I'm hesitant to explain anything!
Tasks are still functional, we just decide whether to use the old style of Tasks or the new style of purity inference based on the following three rules:
Sam Mohr (Nov 22 2024 at 06:39):? is still present, but will be removed at least for now, since it desugars with Result.try instead of the try keyword with early returns
Sam Mohr (Nov 22 2024 at 06:40):So it's still in the language, but in a month or so it's probably gone. Basically, whenever we remove tasks
jan kili (Nov 22 2024 at 06:42):True, but if in the next week we ensure that every AoC-friendly platform requires main!, then to a newcomer the concept of tasks is fully implicit and the tutorial should never capitalize the word.
Sam Mohr (Nov 22 2024 at 06:42):The try keyword is much simpler to understand now IMO, since it just does what Rust does. it desugars to
when thingYouTried and the args is
Ok val -> val
Err err ->
return Err err
I can't think of a reason the word Task, uppercase or lowercase, should be preserved at all in the tutorial. Though I'm open to being wrong
jan kili (Nov 22 2024 at 06:44):In that example, does the type of err appear in the trying function's type signature?
Sam Mohr (Nov 22 2024 at 06:44):Yes
jan kili (Nov 22 2024 at 06:46):I may be being overly pessimistic (or exhibiting an "old dog new tricks" stiffness). Also, AoC is both an opportunity for adoption and an opportunity for constructive feedback on Roc's recent choices.
Sam Mohr (Nov 22 2024 at 06:47):So for example
parseThenDoubleAndPrint! = \strNum ->
num = try Str.toU64 strNum
doubled = num * 2
try Stdout.line! "$(Inspect.toStr doubled)"
Ok {}
Would infer type Str => Result {} [InvalidNumStr, StdoutErr _]
jan kili (Nov 22 2024 at 06:50):Sweet! Like this? https://github.com/roc-lang/basic-cli/pull/257#discussion_r1853325645 (comment on line 11)
jan kili (Nov 22 2024 at 06:51):In other words, jinx, cause I forgot to hit submit on the PR review until now.
Sam Mohr (Nov 22 2024 at 07:16):Yes, but replace the a with the actual error type
Brendan Hansknecht (Nov 22 2024 at 15:13):Also, though task still exists, it is deprecated and will be removed once purity inference is fully working and things are updated.
jan kili (Nov 22 2024 at 21:07):Just a tracking issue for my in-progress tutorial work: https://github.com/roc-lang/roc/issues/7242
Brendan Hansknecht (Nov 23 2024 at 18:35):found a bug
Brendan Hansknecht (Nov 23 2024 at 18:35):If a platform exposes a function like respond! and the implementation in the app uses no effects, it generates a warning
Brendan Hansknecht (Nov 23 2024 at 18:35):It is valid for the app to implement respond! with a simple static response that uses no effects
Brendan Hansknecht (Nov 23 2024 at 18:36):So we should not check the ! effectfulness over the platform to app boundary
Sam Mohr (Nov 23 2024 at 18:37):Yeah, I noticed that as well. We could add a constraint to all top-level defs to allow them to be effectful without an effectful body?
Brendan Hansknecht (Nov 23 2024 at 18:37):I think it would be best if we make a special exception just for the platform
Brendan Hansknecht (Nov 23 2024 at 18:38):Other locations this shouldn't happen
Agus Zubiaga (Nov 23 2024 at 18:38):Yeah, good catch. It should definitely be only for functions provided to the platform.
Agus Zubiaga (Nov 23 2024 at 18:40):Top-level defs are the main motivation for this warning since those are the functions you can call from far away. Disabling it for all of them would kind of defeat the purpose.
Brendan Hansknecht (Nov 23 2024 at 18:52):Yeah, I think it should just be an exception for the functions specified in the provides.
Agus Zubiaga (Nov 23 2024 at 19:10):I’ll look into it tonight
Agus Zubiaga (Nov 27 2024 at 17:10):Fixed in #7254
jan kili (Nov 29 2024 at 23:46):Should this file of Result parsing/trying examples (linked from the tutorial) include versions using the new try keyword?
CC @Anton @Aurélien Geron
Luke Boswell (Nov 30 2024 at 00:03):Yes - that would be good :thumbs_up:
jan kili (Nov 30 2024 at 00:10):Tutorial PR mostly finished - final additions coming tomorrow, ready for primary feedback whenever, hoping to merge tomorrow
https://github.com/roc-lang/roc/pull/7274
(TODO: purity inference previews, Result examples file additions)
Aurélien Geron (Nov 30 2024 at 10:00):JanCVanB said:
Should this file of Result parsing/trying examples (linked from the tutorial) include versions using the new
trykeyword?
CC Anton Aurélien Geron
Thanks for the heads up. I'm on vacation without my laptop, I'll be back home on Thursday. If it can wait until then, I'm happy to update the example. :+1:
Last updated: Jul 26 2025 at 12:14 UTC