parTraverse

fix

OptionOf

Option

fun h(): Option<Int> {
    val x : OptionOf<Int> = None
    val y = x
    return y
}

y

.fix()

OptionOf<Int>

kotlin:ank:playground
import arrow.core.Some
  
//sampleStart
val someInt = Some(1).map { it + 1 }
//SampleEnd
 
fun main() {
   println("value = $someInt")
}

typeclass Monoid {
    fun Self.combine(b: Self): Self
    fun Companion.empty(): Self
}

extension Int : Monoid {
    fun Int.combine(b: Int): Int = this + b
    fun Int.Companion.empty(): Int = 0
}