kotlinlang #arrow

yeah, also if you want to use those combinators are always available inside the Monad binding or fx blocks because the continuation also implements Monad which inherits the entire Functor hierarchy based on the continuation level you are using. The Concurrent cancelable continuations have access to the concurrent combinators as well but the regular monadic ones don't.

👍 1

raulraja

03/05/2019, 4:15 PM

@Jannis https://github.com/1Jajen1/propCheck awesome stuff 👏

🎉 6

Jannis

03/05/2019, 4:18 PM

Thanks for posting 👍 The current version is very close to stable so feel free to test and break it 😅 Feedback is highly appreciated

sam

03/05/2019, 5:21 PM

It looks fantastic. I'm hoping to persuade @Jannis to contribute some of these great features into KotlinTest's own property testing so people already using KT can benefit directly.

K 2

sitepodmatt

03/06/2019, 3:45 AM

Copy code

data class User(val id: Int) {
    companion object
}


interface Eq<F> {
    fun F.eqv(b: F): Boolean

    fun F.neqv(b: F): Boolean =
        !eqv(b)
}

@extension
interface UserEq: Eq<User> {
    override fun User.eqv(b: User): Boolean = id == b.id
}

class ArrowExperiments : StringSpec({

    "arrow experimenting" {
        val u1 = User(1)
        val u2 = User(1)
        //u1.eqv(u2)?
    }
})

sitepodmatt

03/06/2019, 3:45 AM

how do I call eqv on u1 ? I get unresolved reference

jacob

03/06/2019, 3:50 AM

don't you need to use User.eq().run { User(1).eqv(User(2)) } ?

jacob

03/06/2019, 3:50 AM

or something along those lines?

sitepodmatt

03/06/2019, 3:59 AM

Not sure. https://arrow-kt.io/docs/patterns/glossary/ the example stops dead

jacob

03/06/2019, 3:59 AM

lemme see if I can get something running locally. which version of arrow are you using?

👍 1

sitepodmatt

03/06/2019, 3:59 AM

I have no eq() though on User

sitepodmatt

03/06/2019, 3:59 AM

0.8.2

jacob

03/06/2019, 4:03 AM

cool man, gimme 2

jacob

03/06/2019, 4:20 AM

well, the good news is it's not just you 😛

nkhalasi

03/06/2019, 4:26 AM

@jacob @sitepodmatt here is a working example of the Eq typeclass. Do take a look at README

_nkhalasi-kotlin-typeclasses-e2165dd04b15.zip

jacob

03/06/2019, 4:28 AM

looks like it's missing a @higherkind

jacob

03/06/2019, 4:28 AM

@sitepodmatt

jacob

03/06/2019, 4:29 AM

wait

jacob

03/06/2019, 4:29 AM

nope

nkhalasi

03/06/2019, 4:32 AM

Nope...you just need to generate the extension methods and include the generated source in your classpath.

jacob

03/06/2019, 4:33 AM

@sitepodmatt whhy are you redefining Eq?

sitepodmatt

03/06/2019, 4:33 AM

getting confused now, I thought kapt via gradle did that?

sitepodmatt

03/06/2019, 4:34 AM

It was just one of the first simple example in the docs I wanted to see how things all fit together

jacob

03/06/2019, 4:35 AM

ah, ok. I think there might be some confusion. Arrow already ships with Eq that you can just use. Eq is a typeclass where you can define your own instance of that typeclass for your user type

nkhalasi

03/06/2019, 4:38 AM

yes kapt via gradle will generate that. But until that extension method

eq()

is generated for your

User

class (

User.eq()

), the code won't compile. So while its not very clear in the documentation, I found that

kaptKotlin

is an pre-requisite for being able to use the required/expected extension methods.

sitepodmatt

03/06/2019, 5:34 AM

Copy code

package personal.user.eq

import kotlin.Boolean
import kotlin.Suppress
import kotlin.jvm.JvmName
import personal.User
import personal.User.Companion
import personal.UserEq

@JvmName("neqv")
@Suppress(
        "UNCHECKED_CAST",
        "USELESS_CAST",
        "EXTENSION_SHADOWED_BY_MEMBER",
        "UNUSED_PARAMETER"
)
fun User.neqv(arg1: User): Boolean = personal.User.eq().run {
  this@neqv.neqv(arg1) as kotlin.Boolean
}

fun Companion.eq(): UserEq = object : personal.UserEq {  }