Betterwhen.kt

class BetterWhen<T, R>(val appl: T) {

  var result: R? = null

  fun cond(p: (T) -> Boolean, res: () -> R) {
    if (p(appl)) {
      result = res()
      throw Interrupt()
    }
  }

  class Interrupt : Exception()
}

fun <T> betterWhen(rec: T, block: BetterWhen.() -> Unit): R? {
  val ctx = BetterWhen<T, R>(rec)
  return try {
    ctx.block()
    ctx.result
  } catch (e: BetterWhen.Interrupt) {
    ctx.result
  }
}
    

Sample.kt

fun Int.eq(other: Int): Boolean {
  return this == other
}

fun <A, B, R> ((A, B) -> C).partial(): (A) -> (B) -> C =
  { a ->
     { b ->
        this(a, b)
      }
   }
  
fun sample() {
  val int = 3
  val res = 
  betterWhen(int) {
    cond(::eq.partial()(3)) { "success" }
  }
}