Hi Arrow people, I've got another question on docs...

# arrow

[Mark Fisher]

Hi Arrow people, I've got another question on docs examples. I can't get the "Using DI to inject any object" examples compiling, and I'm getting stuck on them. The docs are here https://arrow-kt.io/docs/patterns/dependency_injection/ my code snippet to attempt similar is in thread...

[Mark Fisher]

import arrow.Kind
import <http://arrow.fx.IO|arrow.fx.IO>
import <http://arrow.fx.extensions.io|arrow.fx.extensions.io>.monadThrow.monadThrow
import arrow.typeclasses.MonadThrow

class MyProcessor {
    fun getSomeList(id: String): List<String> {
        return listOf("a-$id", "b-$id")
    }
}

interface SomeDeps<F>: MonadThrow<F> {
    fun processor(): MyProcessor

    companion object {
        operator fun <F> invoke(ME: MonadThrow<F>, processor: MyProcessor): SomeDeps<F> =
                object: SomeDeps<F>, MonadThrow<F> by ME {
                    override fun processor() = processor
                }
    }
}

object Api {
    fun <F> SomeDeps<F>.getFoo(fid: Kind<F, String>): Kind<F, List<String>> =
            fx.monadThrow {
                val (id) = fid
                processor().getSomeList(id)
            }.handleError {
                listOf()
            }
}

fun main() {
    val deps = SomeDeps(IO.monadThrow(), MyProcessor())
    // can't do this:
    // deps.getFoo(...)
}

I had to add a lot more <F> types to the definitions than are in the documented example just to compile. Now I'm trying to invoke deps.getFoo() in main() but the method isn't found.

[Mark Fisher]

Can you tell me what I'm doing wrong?

[aballano]

since getFoo is defined as an extension function, you need to create a context for it, in your case

Api.run {
  deps.getFoo(...)
}

[Mark Fisher]

aha, thanks

[Mark Fisher]

Another question, I can't get the lower part to work either, in the docs it has:

with (Option.monadError()) {
  createId("123") shouldBe Some(123)
  // ...

but createId is on monadThrow not monadError so this doesn't compile either.
How do I get a monadThrow from an Option to make this work?