scala.util.Try[T] と同様に使える Throwable \/ T の型エイリアス

Tries.scala

import scalaz._

/**
  * Tries[T] is a type alias of Throwable \/ T.
  * It can be used in the same manner as scala.util.Try but it is an instance of monad unlike Try.
  *
  * Created by phenan on 2017/10/18.
  */
package object tries {
  type Tries[+T] = Throwable \/ T

  object Tries {
    def apply [T] (v: => T): Tries[T] = try \/-(v) catch { case e: Throwable => -\/(e) }
  }

  object Succeeds {
    def apply [T] (v: => T): Tries[T] = \/-(v)
  }

  object Fails {
    def apply (e: => Throwable): Tries[Nothing] = -\/(e)
  }

  implicit class TriesUtil [T] (t: Tries[T]) {
    def filters (f: T => Boolean): Tries[T] = t match {
      case \/-(v) if f(v) => \/-(v)
      case \/-(v) => -\/(new NoSuchElementException("Predicate does not hold for " + v))
      case -\/(e) => -\/(e)
    }

    def catches (f: PartialFunction[Throwable, T]): T = t match {
      case \/-(v) => v
      case -\/(e) if f.isDefinedAt(e) => f(e)
      case -\/(e) => throw e
    }
  }
}

/ の filter は Throwable が Monoid でないため使えないので、代わりに filters メソッドを用意。
catches は try-catch みたいに使えるように用意してみた。