scala-cats - 如何将 Kleisli[Try, I, A] 转换为 I => A

Question

是否有现有的组合器或更好的编写方式？

def combine[I, A](k: Kleisli[Try, I, A], default: A) : I => A =
  k.run.andThen(_.getOrElse(default))

Answer 1

可以使用 Identity 对一元值进行映射：

def combine[I, A](k: Kleisli[Try, I, A], default: A): I => A =
  k.mapF[Id, A](_.getOrElse(default)).run

例子：

scala> val div = Kleisli[Try, Int, String](x => Try(1000 / x).map(_.toString))
div: cats.data.Kleisli[scala.util.Try,Int,String] = Kleisli(<function1>)

scala> combine(div, "Good")(10)
res0: String = 100

scala> combine(div, "Division by zero")(0)
res1: String = Division by zero