Here is a draft of my post "How to build REST API ...

# arrow

[Rafal Piotrowski]

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 🙂

[pakoito]

I'd say you could work with 0.10-SNAPSHOT because the release is imminent and you'll be able to leverage IO.effect. I don't know if it's too much of a rewrite then 😄

I'll keep on reading.

[pakoito]

override fun findAll(): IOOf<List<Employee>> = IO {

in there you can make it return IO<List<Employeee>> and the compiler won't complain!!

[Rafal Piotrowski]

Is there any date or roadmap for 0.10.0 ?

[raulraja]

it´s about to come out

[raulraja]

we are finishing up some bugs

[pakoito]

that Suspendable typeclass kiss fingertips

[raulraja]

also please consider adding your article to the arrow blog https://github.com/arrow-kt/arrow/issues/new?assignees=MaureenElsberry&labels=Media+Resource&template=add-community-resource.md&title=%5BAdd+Media%5D 🙂

[Rafal Piotrowski]

So I will need to update article soon 🙂

[pakoito]

I love the approach, it leverages typeclasses perfectly

[pakoito]

you got it perfectly right, support for either kind of routing with rx or IO by bridging to suspend

[pakoito]

I don't believe we have Suspendable typeclass in the repo, do we?

[pakoito]

through any other means?

[streetsofboston]

Nice article!
One question: Why is the code in your examples calling runBlocking { ... }? I think wrapping it in runBlocking is not necessary. The call to suspendCoroutine { ... } is enough, I think.

[Rafal Piotrowski]

@pakoito It seems that Suspendable is not in 0.10.0-SNAPSHOT I got wrong impression about it talking with @simon.vergauwen I'll remove info about this class in 0.10.0 release of Arrow from my article

[pakoito]

@streetsofboston you cannot call suspend functions on suspendCoroutine. launch is the equivalent of unsafeRunSync, except that it swallows all errors and doesn't wire cancellation and you have to fix that.

Getting everything piped together is a bit messy. We've done it tho.

[pakoito]

For this article's purposes it's close enough 🙂

[Rafal Piotrowski]

Well, it works without runBlocking since suspendCoroutine is invoked in suspend fun, good catch @streetsofboston 👍

[Robert Menke]

Great article! We just built out a rest API at work with ktor, arrow, and requery and this was a great reference! Using the typeclasses the way you did was brilliant. Thanks!

[Bob Glamm]

I like the with (employeeRouting) { ... } construct; that suggests to me it is possible to aggregate typed routes, similar to the syntax enabled by http4s

[Bob Glamm]

I still want to see if it is possible to use call differently, though

[simon.vergauwen]

I like the with (employeeRouting) { ... } construct; that suggests to me it is possible to aggregate typed routes, similar to the syntax enabled by http4s

That’s a technique @raulraja has used to combine dependencies for a receiver. https://gist.github.com/raulraja/62de72039b11b05ed6d472cb8178da0c

[simon.vergauwen]

If you can share some code, or the desired syntax and the types involved I’d happily take a look

[Bob Glamm]

TBH I think between you, @raulraja and @pakoito all of the code has already been written

[raulraja]

with compiler plugins that technique is gonna be obsolete because we have injectable coherent type classes injected in the this scope automatically

[Derek Seroky]

@Rafal Piotrowski Thanks for writing this! I've been dying for some articles on Arrow+Ktor and I just so happen to use requery as well. I've been using exclusively Kotlin for almost two years now on Android and recently on a mobile API using Ktor. I'm still new to FP but I love it and try and use it as much as I can on Android and with Ktor.

[Rafal Piotrowski]

You welcome @Derek Seroky. Some time ago I was searching Internet a lot to find a way to integrate Ktor with Arrow and I found almost nothing. So when I finally did that and had some time I wrote the above article. I hope it will be helpful for others.

[Rafal Piotrowski]

About requery: I was first using https://github.com/davidmoten/rxjava2-jdbc but there is too much SQL to write when using it, with requery there is some magic related to annotation processor, but there is no need to write SQL queries, CRUD operations are already implemented.

[Derek Seroky]

Requery definitely makes some things easier, though I've been bitten by that "magic" (especially around relationships) and sometimes wished I could just write the SQL. I wish there was more documentation, real life project samples or even more of a community around it. If you find any good resources, I would love to look into it more.

Also, on a side note, have you found any persistence frameworks that have any Arrow integrations?

[raulraja]

If someone wants to write a ktor module for arrow there is room for it and we could help

[raulraja]

We are in the process of writing something similar to Doobie that would use the arrow type class hierarchy

[raulraja]

It's in the early stages discussion at 47 or find some other kind to integrate with

[raulraja]

We already have AQL which if we find a target runtime we can interpret to sql

[raulraja]

But that is a DSL is not ment to be used for jdbc queries but data structures instead

[raulraja]

That satisfy the type classes

[raulraja]

Like functor filter and others. It's more like LINQ

[Derek Seroky]

I would definitely be willing to try and help with Ktor module though I'm pretty new to FP so I'm not sure how much of help I would be. Always willing to help contribute where I can even if it means contributing documentation

[raulraja]

I think a first integration is being able to expose ktor endpoints return type to accept IO and behind the scenes run the IO program in a non blocking fashion

[raulraja]

Which would probably be with unsafeRunAsync or similar combinator

[Bob Glamm]

I still think I want to compare ktor to http4s. I'm not convinced that bridging IO is sufficient when the method for forming responses in ktor involves calling mutation methods on the call object supplied as an argument to the endpoint handler in the routing configuration. That doesn't feel very RT to me

[Bob Glamm]

yeah, a quick look over http4s suggests to me that response objects are RT, usually created by constructors (e.g. Response(status=200, headers=(/* map literal */), "body")) or by pure functions that return a new copy of the response object (e.g. Response(...).addCookie(_ => ...)) Definitely at odds with ktor's mutational methods on call

[Derek Seroky]

@raulraja Is the IO api stabilizing in 0.10.0? I've been avoiding using it since there was some discussion a few months ago about the API being re-worked. We've been basically just marking code with comments that will need to be refactored to use the new IO api once it is completed.

[simon.vergauwen]

The API of IO is stable in 0.10.0. Any chances to it’s API will only be additional combinators, beside any normal activity of course.