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Example of Kleisli composition of Either
object KleisliValidation extends App {
import scalaz._
import Scalaz._
import scala.util.control.Exception._
type EEither[+T] = Either[String, T]
def toDouble(s: String): EEither[Double] = allCatch.either(s.toDouble).fold(_.toString.left, _.right)
def sqrt(d: Double): EEither[Double] = if (d >= 0) math.sqrt(d).right else "sqrt(%s) is too complex for me".format(d).left
val composed = Kleisli(toDouble _) >==> sqrt
Left(sqrt(-2.0) is too complex for me)
Left(java.lang.NumberFormatException: For input string: "hi")
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