kotlinlang #arrow

Hey guys. I am here again with another gist of around 50 lines, and along with it 7 questions. Again I am really sorry I am doing like this, but I thought 1. I don’t want to spam the channel, and 2. Gist can found easily than scrolling slack conversation. I have tried `fx`’s

parTraverse

and it works after spending my whole Sunday to make it work, but I can’t grasp why it works. Thus the questions. Can you help me understand it please. Here is the gist : https://gist.github.com/satyamagarwal/336f02954fa4dc369fdea6524f593d1a

👍 3

sam

07/29/2019, 8:51 PM

What about if you wanted an Either for something that isn’t really suspendable, like say parsing a string to an int? In that case Either.catch wouldn’t work ?

Bob Glamm

07/30/2019, 2:18 AM

fun <F> IO<F>.runner(connection: Connection): JDBCOps<F> =
        object: JDBCOps<F>, Fx<F> by this, Bracket<F, Throwable> by this {

doesn't work because Fx<F> is not Bracket

pakoito

07/30/2019, 5:29 PM

it's supposed to be there

PhBastiani

07/31/2019, 3:25 PM

What do you mean by

Free.monad()

Today, i tried to translate de Scala Cats sample into Kotlin (see https://gist.github.com/PBastiani/3598c838cbfdd982238360244b7550ed) Something seems wrong in the interpreter : i understand that in my FREE program

FreeKVStore<Unit>

is in conflict with

Kind<F, A>

! But, I don't know how to fix that...

carbaj0

08/01/2019, 10:21 AM

hello, i have this issue when try to generate an app Android

Bob Glamm

08/01/2019, 2:30 PM

Yeah, there is a diagram for each type, but I'm talking an integrated diagram like https://github.com/tpolecat/cats-infographic that shows everything on one page

Ryan Benasutti

08/04/2019, 4:03 AM

Is there something similar to

IO.handleError { }

that doesn't require I provide an

IO<A>

(perhaps one which requires an

IO<Unit>

)? I have a method which returns an

IO<A>

, but I need to guarantee certain additional IO operations happen if the former IO fails (and in this case, I can't return an

IO<A>

because that part failed).

Bob Glamm

08/05/2019, 12:55 PM

ok, in the applicative case I can see that working, but if I have (say)

val (r1) = query("...", mapper1); val r2 = computation(r1); val (r3) = update("...");

then I'm back to monads and trying to run suspend blocks outside of coroutine scope if I don't have

fx

nested inside

transaction

rcd27

08/06/2019, 9:37 AM

Need some help with

MapK.traverse(..)

method. Any code of how to use it?

Pagoda 5b

08/06/2019, 12:02 PM

Hi and hello, did anyone has issues with using concurrent.fx notation on kotlin 1.3.41, with the code generation error during compilation phase?

compiler-error

pakoito

08/06/2019, 1:27 PM

@Bob Glamm see if this helps: https://arrow-kt.io/docs/patterns/dependency_injection/#disambiguating-colliding-instances

simon.vergauwen

08/06/2019, 7:07 PM

Personally I almost always prefer

followedBy

over

flatMap { _ ->

bind

😲 1

Satyam Agarwal

08/06/2019, 7:20 PM

Also, most web apps today brings side effects from the very bottom. Like repositories (http call or db call), so most of the functions would have returning type as IO<A>. That being said, do I gain anything except for
direct imperative syntax
(which i am not leveraging here) from a function with returning type IO if I execute my IOs in fx ? for example :

import <http://arrow.fx.IO|arrow.fx.IO>
import arrow.fx.extensions.fx

fun someFun(): IO<Unit> = IO { println("hey") }
fun anotherFun(): IO<Unit> = IO { println("hey again") }

fun main() {
    someFun().followedBy(anotherFun()).unsafeRunSync()
}

fun mainMain() {
    IO
        .fx {
           someFun().followedBy(anotherFun()).bind()
        }
        .unsafeRunSync()

}

main()
mainMain()

pakoito

08/06/2019, 8:19 PM

many things are semigroupal: numbers, collections, strings, functions, even rx.Observable is semigroupal

Bob Glamm

08/07/2019, 1:21 PM

awesome, I now have a little library that lets me express database transactions under fully polymorphic effects as follows:

fun <A> service(): Kind<F, A> = transaction {
    val (r1) = query(QUERY1, query1Mapper)
    val (r2) = query(QUERY2, query2Mapper)
    combine(r1, r2)
}

Now to add things like better update/insert support and eliminate some ugly refs to

fx.monadThrow

within the mappers. Could not have done this without your help. Thanks!

❤️ 4

carbaj0

08/09/2019, 6:24 AM

message has been deleted

noiano

08/09/2019, 8:15 AM

so I guess there’s no way I go from

(List<Try<A>>) -> List<A>

with a simple flatmap

Robert Menke

08/10/2019, 8:13 PM

Has

OptionT

(or any of the

MonadT

) constructors been moved/replaced in the 0.10.0-snapshot? Can’t seem to figure out how to import/install them.

Robert Menke

08/11/2019, 1:22 AM

Gotcha that makes sense @pakoito thanks for the explanation. 🤞 for KEEP87 😉.

thanh

08/11/2019, 5:23 PM

Anyone acknowledge any library that supports those convenient functions for using Arrow data types with RxJava like this one?:

fun <T, R> Observable<Either<Throwable, T>>.flatMapEither(mapper: (T) -> Observable<R>): Observable<Either<Throwable, R>> {
    return flatMap {
        when (it) {
            is Either.Right -> mapper(it.b).map { it.right() as BeckonResult<R> }
            is Either.Left -> Observable.just(it)
        }
    }
}

thanh

08/11/2019, 5:42 PM

it is just a bit complicated to introduce to our code base now 😞 We are even not very comfortable with concept of Traversable.

Ryan Benasutti

08/11/2019, 7:18 PM

Using

ListK.applicative()

and

tupled(listA.k(), listB.k()

, I can generate all `Tuple2`'s with the elements in both lists. If I give more arguments to

tupled

, then I get a

Tuple3

, etc. Is there a way to give more arguments to a method like

tupled

but still only get a

Tuple2

out? I want to get all the pairs of elements between n lists.

Bob Glamm

08/11/2019, 7:44 PM

Comments/suggestions/PRs/etc. welcome

stojan

08/12/2019, 6:15 AM

just wanna say amazing work with Ank ♥️

🎉 8

Derek Berner

08/12/2019, 9:51 PM

My problem is the opposite - I've had a good handle on this stuff for maaaaaaybe a few months, and now I can't unsee it, and I keep getting told to not use these abstractions because they're confusing the junior devs 😂

😂 1

aeruhxi

08/13/2019, 7:21 AM

fun <K, V, R> Map<out K, V>.map(
    transform: (Entry<K, V>) -> R
): List<R>

Why does

map

for

Map

in stdlib return

List

instead of

Map

Bob Glamm

08/13/2019, 2:05 PM

University of Minnesota - Twin Cities. EE major, so I am an expert in how to short out power supplies to spectacular effect.

😂 2

Bob Glamm

08/13/2019, 2:06 PM

you?