Georges Boris (Dec 25 2024 at 18:04): Georges Boris (Dec 25 2024 at 18:04):Hey folks - I'm trying to use the record builder syntax but I think there is something outdated between builtin docs and the tutorial.
Ref:
https://www.roc-lang.org/tutorial#record-builder
https://www.roc-lang.org/builtins/Task#batch
How would I use the record builder syntax these days with a Task?
My code as example using the basic-webserver@0.10 platform:
{ Task.ok <-
a: Env.var "A",
b: Env.var "B"
}
Oh, sorry, that's out of date yes
Sam Mohr (Dec 25 2024 at 18:33):Record builders used to be built with applicative functors
Sam Mohr (Dec 25 2024 at 18:33):Which was a complex tool for beginners to grok
Sam Mohr (Dec 25 2024 at 18:34):So now we just accept any function that takes two things and combines them
Sam Mohr (Dec 25 2024 at 18:35):So Task.batch is for the old style, and we don't have a function for the new style
Georges Boris (Dec 25 2024 at 18:35):Oh wow! Yeah - I was still under the impression it was related to applicatives.
Anthony Bullard (Dec 25 2024 at 18:36):The tutorial needs some love
Sam Mohr (Dec 25 2024 at 18:37):combineTasks : Task a err, Task b err, (a, b -> c) -> Task c err
combineTasks = \leftTask, rightTask, combiner ->
left = leftTask!
right = rightTask!
Task.ok (combiner left right)
This function should be a userspace record builder combiner
Sam Mohr (Dec 25 2024 at 18:38):With Purity Inference, you shouldn't really need this
Sam Mohr (Dec 25 2024 at 18:41):But you could do this:
combine! : ({} => Result a err), ({} => Result b err), (a, b -> c) => Result c err
combine! = \leftGen, rightGen, combiner ->
left = try leftGen! {}
right = try rightGen! {}
Ok (combiner left right)
Why does it need to be a userspace function? Shouldn't it be part of the Task module?
Sam Mohr (Dec 25 2024 at 18:46):It should, but Task is going the way of the dodo pretty soon
Georges Boris (Dec 25 2024 at 18:46):Maybe I'm misinterpreting what userspace means :grinning_face_with_smiling_eyes:
Sam Mohr (Dec 25 2024 at 18:46):I guess I could add that just as a stopgap
Georges Boris (Dec 25 2024 at 18:46):Ohhh right - with the purity inference thing
Sam Mohr (Dec 25 2024 at 18:46):Not sure what the right name is.
Sam Mohr (Dec 25 2024 at 18:46): Sam Mohr (Dec 25 2024 at 18:46):What would you prefer?
Georges Boris (Dec 25 2024 at 19:08):combine makes sense to me! I like that it seems like a reusable name for the pattern to be used in different modules.
Sam Mohr (Dec 25 2024 at 19:09):I'll make a PR, then
Sam Mohr (Dec 25 2024 at 20:01):@Georges Boris could you look at https://github.com/roc-lang/roc/pull/7413 if you get a chance and tell me if the docs make sense to you?
Sam Mohr (Dec 25 2024 at 20:02):It's pretty simple
Georges Boris (Dec 25 2024 at 20:29):Looks good to me!
I wonder if it wouldn't be better to remove the previous batch example as a whole since that code doesn't compile anymore.
Sam Mohr (Dec 25 2024 at 20:29):Yeah, probably the right move
Sam Mohr (Dec 25 2024 at 20:30):done
Last updated: Jul 26 2025 at 12:14 UTC