kotlinlang #arrow

Hi @Bob Glamm, I saw in the channel history that you were working with ktor and you were trying to use IO as a ktor handler (which is suspended function). Have you managed to do that using Arrow 0.9.0 or you had to use snapshot version (0.10.0-SNAPSHOT)?

Bob Glamm

08/15/2019, 7:55 PM

I'm not convinced these adapters I'm trying to write are the right way to go about doing this. @pakoito @raulraja @simon.vergauwen thoughts on transforming

Route.get(path: String, body: suspend PipelineContext<Unit, ApplicationCall>.(Unit) -> Unit): Route

from something more like

Route.get(path: String, body: Async<F>.(ApplicationCall) -> Kind<F, Unit>): Route

? I keep running into issues where trying to just transform the second argument from

Async

PipelineContext

cannot resolve

.fix().suspended()

to end up with

suspend () -> Unit

Rafal Piotrowski

08/19/2019, 12:43 PM

Hello, I have integrated Arrow with Ktor using

Deferred

class from

kotlinx.coroutines

, sample code is below. As you can see I have

DemoService

and

DemoRouting

which have no suspend method and are parametrized with type

. I define

IO

when the server is created (so on the end of the world ;)). I could use different monad (e.g.

Try

) after implementing the

Deferrable

interface. Please let me know what you think about this approach. @Bob Glamm, this is a little bit different than using

Async

directly as we spoken recently, there is a separate typeclass to transform value into deffered value.

Untitled

miqbaldc

08/21/2019, 7:28 AM

is there any java alternative e.g:

arrow-java

raulraja

08/21/2019, 10:01 AM

I'm sure there is also some meta lib for java out there we may not know about doing something similar or providing the primtives to do it with javac that isn't apt

LeoColman

08/21/2019, 8:21 PM

This would be something like

try {
  foo()
} catch(FooException) { 
} catch(BarException) { }

raulraja

08/21/2019, 10:29 PM

Maybe you are looking for

SequenceK

raulraja

08/24/2019, 12:17 PM

If you have an opinion and agree we could propose comprehensions for Kotlin and get rid of bind in in Arrow

👏 4

Brandon Ward

08/26/2019, 10:08 PM

which dependencies for arrow 0.9.0 do I need to use to get access to

IO

? The docs are unclear and refer to dependencies that don't exist for this version, or don't exist at all.

PhBastiani

08/27/2019, 12:09 PM

Hi, I'm discovering the new

fx

syntax for comprehensions... If i understand, the new impl uses coroutines under the cover ! I replaced the calls of

bindind()

fx.monad

Now, I have something like that :

fx.monad {
    val vMaybe:Option<T> = ...
    vMaybe.map { mymonadfunction(...).bind() }
   ...

Here, the call of

bind()

gives me an error 'Suspension functions can be called only within coroutine body'... What is the new syntax for this kind of binding ? Thx in advance....

Bob Glamm

08/27/2019, 12:59 PM

fx.monad {
    val v: T = !foo(x)    // fun foo(x: Any): Option<T>; v is bound to T since ! is an alias of bind()
    !mymonadfunction(v)    // fun mymonadfunction(t: T): Option<R>; value of fx.monad {} block will be Some(R) or None
}

Rafal Piotrowski

08/28/2019, 9:02 AM

Here is a draft of my post "How to build REST API with Arrow, Ktor and requery in Kotlin": https://medium.com/@rafal.piotrowski/e5438c951418 Any feedback is welcome 🙂

⭐ 2

:arrow: 8

🙂 4

Robert Menke

08/28/2019, 3:34 PM

What is the practical difference between a semigroup and a monoid? Both seem to be mechanisms for combining things together

Sergey Akhapkin

08/28/2019, 8:26 PM

Hello, everyone. Could you pls help me - just started to use Arrow, so perhaps did something wrong (e.g. forgot to import something). My question is - why there is difference how Try works in Arrow and Scala ?

import arrow.core.*
Try.invoke { "1" }.flatMap<Int> { throw IllegalArgumentException() }
java.lang.IllegalArgumentException

scala.util.Success<String>("a").flatMap<Int> { throw IllegalArgumentException() }
res28: scala.util.Try<kotlin.Int!>! = Failure(java.lang.IllegalArgumentException)

or in native Scala REPL:

System.out.println(scala.util.Try("x").flatMap{ s => throw new java.lang.IllegalArgumentException(s) })
> Failure(java.lang.IllegalArgumentException: x)

Bob Glamm

08/29/2019, 1:06 PM

I sure wish I could make it to Cádiz. Will that presentation be available online after the conference?

PhBastiani

08/29/2019, 3:48 PM

Hi, is-it possible to have a partial lifting into an Arrow Free Monad ?

pakoito

08/30/2019, 10:43 AM

I believe this one is for the debugger, I've been able to repro but cannot dig into what happens when

!put("A", 1)

is called. We know it never reaches the interpreter.

Ryan Benasutti

08/30/2019, 10:12 PM

Is there already an arrow + hamkrest library out there? I find myself writing a lot of extra hamkrest matchers for arrow data types and I don't want to release my own library if there's already one I should know about

pakoito

08/31/2019, 8:48 PM

Coproduct/HList

raulraja

08/31/2019, 10:50 PM

There is no need to nest this function on a Kind F.

suspend fun String.parseDate(): Either<DateParseError, Date> =
  Either.catch({ e -> DateParseError(e) }) {
     dateFromString(this)
  }

raulraja

09/01/2019, 12:06 AM

This is more inline also with Arrow and Fx expecting side effects including things that can fail inside suspension or IO

👍 1

Bob Glamm

09/01/2019, 2:40 AM

ugh, I think the best I can do is a typed method that yields a program that properly binds the parameters to PreparedStatement. Yuck.

Fred Friis

09/02/2019, 3:39 AM

Can someone explain the differences between

Option.else

Option.getOrElse

and

Either.filterOrElse

Either.filterOrOther

AdrianRaFo

09/02/2019, 8:10 AM

@Fred Friis -

Option.getOrElse

returns the value inside if the

Option

is a

Some

or return the provided param if it's a None -

Option.orElse

returns the same

Option

if it's not

None

, otherwise returns the provided

Option

The difference here is that

getOrElse

will return the value outside the

Option

context but the

orElse

keep that context

☝️🏽 1

simon.vergauwen

09/03/2019, 1:47 PM

Applicative

enables combining elements using

map

for any number of arguments 🙂

raulraja

09/03/2019, 2:58 PM

data class Data(val a: String, val b: String)
data class Error(val msg: String)
val data : Either<Error, Data> = Either.applicative<Error>().map("".right(), Error("oops").left(), ::Data).fix()
//Left(Error("oops"))

👍 1

Title

raulraja

09/03/2019, 2:58 PM

data class Data(val a: String, val b: String)
data class Error(val msg: String)
val data : Either<Error, Data> = Either.applicative<Error>().map("".right(), Error("oops").left(), ::Data).fix()
//Left(Error("oops"))

👍 1

@carbaj0 the issue is the applicative instance is incorrectly parameterised

also if you just want to gather results you can use

tupled

map

is only useful if you plan to transform them in the map function otherwise tupled is all you need

☝️ 1

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