tfsample.kt

import io.reactivex.Single
import io.reactivex.functions.BiFunction

interface Kind<out C, out A>

class ForSingle private constructor()
class SingleContainer<T>(val single: Single<T>): Kind<ForSingle, T>
fun <T> Kind<ForSingle, T>.fix() = (this as SingleContainer<T>).single
fun <T> Single<T>.unfix() = SingleContainer(this)

interface Math<F> {

    fun lift(value: Int): Kind<F, Int>

    fun add(value1: Kind<F, Int>, value2: Kind<F, Int>): Kind<F, Int>

}

class RxMath : Math<ForSingle> {

    override fun lift(value: Int): Kind<ForSingle, Int> = Single.just(value).unfix()

    override fun add(value1: Kind<ForSingle, Int>, value2: Kind<ForSingle, Int>): Kind<ForSingle, Int> =
            value1.fix().zipWith<Int, Int>(value2.fix(), BiFunction(Int::plus))
                .unfix()

}

interface Bridge<F, A> {
    
    fun apply(math: Math<F>): Kind<F, A>
    
}

fun RxLift(value: Int) =
        object : Bridge<ForSingle, Int> {

            override fun apply(math: Math<ForSingle>): Kind<ForSingle, Int> {
                return math.lift(value)
            }
            
        }