Simple Kotlin DI

FP Data Flow

package com.fortyseven.fptraining

import arrow.core.Either
import arrow.core.right
import arrow.effects.IO
import arrow.effects.extensions.io.fx.fx

data class Account(val balance: Int)
data class AccountEntity(val balance: Int)

/** User algebras **/
interface UI {
  fun present(): IO<Unit>
}

interface Domain {
  fun getProcessedAccount(): IO<Account>
}

interface Data {
  fun fetchAccount(): IO<AccountEntity>
}

/** interpreters */
object InMemoryData : Data {

  fun retrofit(callback: (Either<Throwable, AccountEntity>) -> Unit): Unit =
    callback(AccountEntity(100).right())

  override fun fetchAccount(): IO<AccountEntity> =
    IO.async { _, callback ->
      retrofit(callback)
    }
}

class DefaultDomain(val data: Data) : Domain {
  override fun getProcessedAccount(): IO<Account> =
    data.fetchAccount().map { Account(it.balance) }
}

class DefaultUI(val domain: Domain) : UI {
  override fun present(): IO<Unit> =
    fx {
      val account = domain.getProcessedAccount().bind()
      !effect { println(account) }
    }
}

class Module(
  data: Data = InMemoryData,
  domain: Domain = DefaultDomain(data),
  val ui: UI = DefaultUI(domain)
) {
  companion object {
    val defaultInstance = Module()
  }
}

fun main() {
  Module.defaultInstance.ui.present().unsafeRunSync()
  
}