ΛRROW/Lobby

http://arrow-kt.io/

Marco Vermeulen

@marc0der

And if you wait until buying it tomorrow, Manning will give you a big 50% discount.

Ming

@noiter

@pakoito on page https://arrow-kt.io/docs/patterns/monads/#monad-laws, when explaining the Associativity law, in the code snippet you would see -> val g: (T) -> Kind<F, V>

Paco

@pakoito

@noiter fixed: arrow-kt/arrow@0af0fb2

@SAGARSURI Marco's book is a potential good start, the equivalent in Scala was very popular.

From us, start here: https://arrow-kt.io/docs/patterns/error_handling/

the thing about FP is that it's not a framework nor an architecure, rather a set of practices such as immutability and purity. Once you start applying those to your code, you start seeing pain points.

and the library addresses those common patterns and pain points

i.e. branching with Either, threading with IO, injection with Reader

you cannot take it all in one go, nor we can teach "FP architecture" on day one

start simple, do immutability everywhere and make any side-effect into a suspend function

see what your paint points are, find the consruct for them

Marco Vermeulen

@marc0der

Couldn't have said it better @pakoito

Paco

@pakoito

I have published a Reference Guide for Arrow-fx 0.10 to get you started!

It covers everything from the basics of wrapping suspend functions and parallelism, to advanced use cases like safe resource management and program structure 📝

https://www.pacoworks.com/2019/12/15/kotlin-coroutines-with-arrow-fx/

Julius Marozas

@jul1u5

Hi, what does the exclamation mark mean in this example: !Observable.interval(100, TimeUnit.MILLISECONDS)? From Observable comprehensions third code block

Bob Glamm

@glammr1

roughly speaking, ! means "do this thing for its effect"

part of the fx syntax

Otherwise Observable.interval(100, TimeUnit.MILLISECONDS).k() is likely just an object wrapping a method reference

Julius Marozas

@jul1u5

So is ! just a function? How is it implemented?

Bob Glamm

@glammr1

I think it is the not extfun but I cannot remember on which interface/typeclass it is defined on

If you load the snippet up in IntelliJ and control/command-click then IntelliJ will display the definition

it is using one of Kotlin's limited operator overloads

Julius Marozas

@jul1u5

Ok, thanks!

Philippe Bastiani

@PhBastiani

@SAGARSURI the book 'The Joy of Kotlin' is also a good start to learn the FP principles.

Benjamin Krenn

@fridayy

hi, I hope this is the right channel to report this. While reading the docs I stumbled across a small mistake:
Error propagation in comprehensions

Both code listings contain the same code

Paco

@pakoito

thanks! I'll put a ticket

arrow-kt/arrow#1894

Raúl Raja Martínez

@raulraja

@jul1u5 ! Is the equivalent suspended imperative version of flatMap

It's going to be replaced for 'by'

a by fa

So you'd have to name each bind and we'll track it to give you an IO trace that is meaningful even when in concurrency or async contexts

! Is define in BindSyntax, an interface all fx blocks have access to

The current implementation is based on suspension and reflection which ties us to the JVM but the upcoming meta impl based on by rewrites bindings to flatMap and discovers flatMap structurally based on the member or extension scope of any given data type

This will unlock comprehensions automatically for all data types in the Kotlin and java ecosystem that have a valid flatMap shape by member or extension

Streams, Completable future, Rx, reactor, coroutinesx Flow etc.

Mochamad Iqbal Dwi Cahyo

@mochadwi

https://www.youtube.com/watch?v=qI1ctQ0293o this content is obsolete.

does the recommended ways for error handling, async handling (io), side-effect

using this from arrow-kt: https://arrow-kt.io/docs/patterns/error_handling/?

Bob Glamm

@glammr1

Long-term it's Either.catch() or Bifunctor IO

for error handling

async and the rest of the effects are spot-on, though

suggest joining #arrow in the kotlinlang slack (kotlinlang.slack.com)

Mochamad Iqbal Dwi Cahyo

@mochadwi

thanks for your response, will move this disscussion to kotlinlang.slack.com

Johann Maquin

@Jmaquin

Hello, I would like to create a State<List<Int>, Int> using the just function, however as per the signature (StateT : fun <F, S, T> just(AF: Applicative<F>, t: T): StateT<F, S, T>) I need an applicative , where can I get the applicative for List<T>? thanks

Bob Glamm

@glammr1

use ListK instead of List then use ListK.applicative()

also suggest joining #arrow in the kotlinlang slack (kotlinlang.slack.com)

Johann Maquin

@Jmaquin

thanks for your response

Gopal S Akshintala

@overfullstack

Does this section of kotlin arrow documentation has any typos? (coz when I try to copy paste the same code and compile it doesn’t work): https://arrow-kt.io/docs/patterns/error_handling/#monaderror

I see arm(ME: MonadError<F, NukeException>) and aim(ME: MonadError<F, NukeException>) are taking input params, but the subsequent code
fun <F> MonadError<F, NukeException>.attack():Kind<F, Impacted> =
fx.monad {
val (nuke) = arm<F>()
val (target) = aim<F>()
val (impact) = launch<F>(target, nuke)
impact
}

fun <F> MonadError<F, NukeException>.attack1(ME): Kind<F, Impacted> =
  ME.tupled(aim(), arm()).flatMap(ME, { (nuke, target) -> launch<F>(nuke, target) })

These functions are called without any arguments, same for attack() function. Am I missing anything?

Paco

@pakoito

you're right

it should be this as an argument, or the functions to be extfuns instead

Danny Kruitbosch

@dannykruitbosch

Hi, I'm trying to use Arrow in a java 11 module (JPMS) based app. When compiling I get this error

java.lang.module.ResolutionException: Modules arrow.core.data and arrow.annotations export package arrow to module kotlin.stdlib.common

. Does anyone know how to resolve this?

Paco

@pakoito

yeah, I don't believe we're there

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