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arrow

Marcin Gryszko

06/25/2019, 5:33 AM

Looking at the fx class hierarchy, I saw that there are two

Fx

interfaces: one declared in

arrow.effects.typeclasses.suspended.concurrent

package (with

IOFx

implementation, another one in

arrow.effects.typeclasses.suspended.monad

(for the rest of monad implementations). Is there a reason that they are separated?

Bob Glamm

06/26/2019, 8:26 PM

but I'm struggling to come up with a real-life example for how to swap out instances of

<F>

in something like the following:

interface S3Ops<F>: MonadDefer<F> {

    val s3: AmazonS3

    fun getS3Info(bucket: String, key: String): Kind<F, S3Object> {

        val waiterRequest = GetObjectMetadataRequest(bucket, key)

        return catch { s3.waiters().objectExists().run(WaiterParameters(waiterRequest)) }
                .flatMap {
                    val objectRequest = GetObjectRequest(bucket, key)
                    catch { s3.getObject(objectRequest) }
                }.flatMap {
                    if (it == null) {
                        raiseError(RuntimeException("No object retrieved from S3"))
                    } else {
                        just(it)
                    }
                }
    }

Imran/Malic

06/26/2019, 9:29 PM

whenever I click on Download sources. It only tells me after the download, that it did not found the sources

Bob Glamm

06/28/2019, 1:56 PM

only a type error in IJ, running the actual compiler works just fine

Derek Berner

06/28/2019, 2:37 PM

Is there currently any advice on building and consuming programs using the

Free

monad? Or should we be preferring

IO

for that?

Derek Berner

06/28/2019, 2:47 PM

(It also turns out I accidentally implemented the

Free

monad in Elm one time because their `Cmd`s were frustratingly not monadic...)

AdrianRaFo

07/01/2019, 9:23 PM

Do we have

flatTap

pakoito

07/02/2019, 9:19 PM

based off the Map implementation I’d suspect

HieiJ

07/04/2019, 8:23 PM

Also, do you have some documentation about how Ref works?

HieiJ

07/05/2019, 11:24 AM

I've made a little post just to create some context... https://www.msec.it/blog/self-contained-example-of-testing-with-modules-and-arrow-fx/ I'm going to open a PR for this hopefully today

Tim Fennis

07/09/2019, 8:07 AM

Damn man, when you guys have discussions like this I feel so dumb

☝️ 3

😔 1

nicopasso

07/09/2019, 9:06 AM

Hey everyone, I’m using (well I’m trying to use 🙂 )

bindingCatch

to compose a sequence of actions (API call, db call etc). What’s the best way to test it and to assure the actions are executed?

than_

07/09/2019, 10:25 AM

hi, there seems to be some changes in library contents in 0.9.1-SNAPSHOT. now i can't find Getter although I have io.arrow-kt:arrow-optics dependency. where do I find optics now? 😮

than_

07/10/2019, 10:20 AM

opened issue on github. thanks for support 🙂

kioba

07/15/2019, 3:41 PM

will there be an Arrow talk this year at KotlinConf?

Jorge Castillo

07/15/2019, 3:48 PM

There might be something 🙂 let’s wait for the official announcements by JetBrains

7️⃣ 1

8️⃣ 1

simon.vergauwen

07/15/2019, 4:08 PM

You can group those dependencies to have the same effect.

data class UseCaseContext(val repo: Repo, val db: Db)

, now your use cases logic is coupled to

UseCaseContext

and you can deal with your dependencies further as you normally would. Interface segregation etc

Bob Glamm

07/16/2019, 3:23 AM

Hopefully @raulraja will correct me where I'm wrong above

Bob Glamm

07/16/2019, 3:32 AM

Also, if I understand it correctly, higher kinds are just type constructors. But don't ask me how

Either l r :: * -> * -> *

is implemented via

Kind<F, A>

in Arrow

simon.vergauwen

07/17/2019, 2:00 PM

You can go from

Flux<A>

suspend () -> List<A>

Mono<A>

suspend () -> A?

carbaj0

07/17/2019, 2:20 PM

because not exist an instance like this

object : FxSyntax<ForIO> by IO.fx() { }

simon.vergauwen

07/17/2019, 2:38 PM

If you have any additional questions to the one I answered in the gist I’d love to help you further solve your problem.

Ryan Benasutti

07/17/2019, 2:39 PM

Why is there no

SetK.applicative()

similar to

ListK.applicative()

sean

07/17/2019, 9:04 PM

Are there any documents for working with

fx

Either

and

coroutines

? I've been going over the documents and feel like I'm just missing something. I see effect but it looks like it's under the IO data type.

HieiJ

07/18/2019, 6:39 AM

Hi all, I've written a little blog post about effect polymorphism with fx: https://www.msec.it/blog/effect-polymorphism-with-arrow-fx/ Since I'm an FP beginner, just experimenting, do you have any comment/correction about this?

dr.dreigh

07/18/2019, 10:53 AM

Did I imagine it or did I see that there is a http lib using Arrow?

Bob Glamm

07/18/2019, 12:30 PM

How do I compose two coroutine libraries together? E.g., trying to bridge

ktor

and Arrow:

val q: (ApplicationCall) -> Kind<ForIO, Unit> = { c -> IO.fx().fx { c.respondText("Foo", ContentType.Text.Html) } }

c.respondText

is a suspending function not in

IO

and

@RestrictsSuspension

IO

prevents the composition from occurring that way

Imran/Malic

07/18/2019, 4:23 PM

Why can I get from every Comonad an Monad, but not the other way around?

Derek Berner

07/19/2019, 3:45 PM

I need to write a "decorator" function that takes in any function with arbitrary args (A,B,C,D,...) -> Z and returns a function of the same type that performs some decoration logic. Does arrow provide capabilities to do this?

simon.vergauwen

07/19/2019, 4:01 PM

Oh okay, you want

leftFlatMap

but that currently doesn’t exist in Arrow.

Title

simon.vergauwen

07/19/2019, 4:01 PM

Oh okay, you want

leftFlatMap

but that currently doesn’t exist in Arrow.

pakoito

07/19/2019, 5:25 PM

handleErrorWith

Robert Menke

07/19/2019, 6:00 PM

If it’s still ok to add

flatMapLeft

I did create a branch with the functionality + test. I get an error pushing my branch up to origin because of permissions. No big deal if you’d prefer not to add extra code to maintain @simon.vergauwen @pakoito. Up to you guys.

pakoito

07/19/2019, 6:00 PM

I';d rather not, we aligned the names not so long ago

and we moved from mapLeft to handleError for example

simon.vergauwen

07/19/2019, 6:01 PM

But this is different from

handleErrorWith

It doesn’t fix

but rather leaves it generic.

It’s an operator of the bifunctor hierarchy, right?

Robert Menke

07/19/2019, 6:04 PM

Cool,

handleErrorWith

does work perfectly for my use case so I can stick with that. Thanks for pointing me in the right direction!

pakoito

07/19/2019, 6:04 PM

flatMapLeft

is a specialized

handleErrorWith

or just a plain alias

simon.vergauwen

07/19/2019, 6:05 PM

It’s the other way around

pakoito

07/19/2019, 6:05 PM

because you can return handleErrorWith { Either.Left("") }

I thought we kept the handleError naming so it was consistent across datatypes

simon.vergauwen

07/19/2019, 6:06 PM

fun <A, B, C> Either<A, B>.leftFlatmap(f: (A) -> Either<C, B>): Either<C, B> = when(this) {
  is Either.Left -> f(this.a)
  is Either.Right -> this
}

fun <A, B> Either<A, B>.handleErrorWith(f: (A) -> Either<A, B>): Either<A, B> = leftFlatMap(f)

I’m not favoring one over the other. I’d include both since I expect

leftFlatMap

to come back when we complete the bifunctor hiearchy.

It’s a very handy operator for

IO<E, A>

over

handleErrorWith

Because it can to change

Nothing

, well I guess you could name it

handleErrorWith

in a bifunctor hierarchy but then it would be an alias. Here it’s not.

@Robert Menke you’re very welcome! Glad to help any time. Sorry for the confusion.

❤️ 1

Robert Menke

07/19/2019, 6:18 PM

So 1 other consideration is that

handleErrorWith

is not an

inline

function so it actually doesn’t work for my use case because I need to call

suspend

functions inside. I can get by with

fold

for now, just voicing my experience.

simon.vergauwen

07/19/2019, 6:20 PM

That is where

IO

comes in,

Either

cannot deal with the powers of

suspend

. It cannot control the async jumps, exception being thrown etc.

Robert Menke

07/19/2019, 6:21 PM

Gotcha 👍 so just out of curiosity (and ignorance) why inline certain functions like

flatMap

fold

but not something like

handleErrorWith

simon.vergauwen

07/19/2019, 6:21 PM

With

IO

you'd do

io.handleErrorWith { e -> IO.effect { suspendFunction() } }

If those functions are still inline then that will probably change soon.

Robert Menke

07/19/2019, 6:28 PM

Ok that makes sense! Thanks!

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