error_handling.kt

import kategory.*

sealed class NukeException {
    object SystemOffline: NukeException()
    object RotationNeedsOil: NukeException()
    data class MissedByMeters(val meters:Int): NukeException()
}

object Nuke
object Target
object Impacted

typealias SystemOffline =  NukeException.SystemOffline
typealias RotationNeedsOil =  NukeException.RotationNeedsOil
typealias MissedByMeters =  NukeException.MissedByMeters

inline fun <reified F> arm(ME:MonadError<F,  NukeException> = monadError()):
        HK<F, Nuke> = ME.pure(Nuke)

inline fun <reified F> aim(ME:MonadError<F, NukeException> = monadError()):
        HK<F, Target> = ME.pure(Target)

inline fun <reified F> launch(target: Target, nuke: Nuke, ME:MonadError<F, NukeException> = monadError()):
        HK<F, Impacted> = ME.raiseError(MissedByMeters(5))

inline fun <reified F> attack(ME:MonadError<F, NukeException> = monadError()):HK<F, Impacted> =
        ME.binding {
            val nuke = arm<F>().bind()
            val target = aim<F>().bind()
            val impact = launch<F>(target, nuke).bind()
            yields(impact)
        }

inline fun <reified F> attack1(ME:MonadError<F, NukeException> = monadError()):HK<F, Impacted> =
        ME.tupled(aim(), arm()).flatMap(ME, { (nuke, target) -> launch<F>(nuke, target) })

fun main(args:Array<String>) {
    attack<EitherKindPartial<NukeException>>() // this will automatically retriev the monad error instance from either
    attack(Either.monadError())
    attack1<EitherKindPartial<NukeException>>()
}

On line 34 you can just use flatMap { (nuke, target) -> launch<F>(nuke, target) } syntax