SmartBuilderWithExceptions.scala

  final class SmartBuilder[A,B](val f: BuildStep[Throwable,A => B])
  {
      def @> [E <: Throwable](step: BuildStep[E,A])(implicit applicative: Applicative[({type f[x] = BuildStep[Throwable, x]})#f]) = {
        applicative.apply(f)(step)
      }
  }

  object SmartBuilderOps
  {
    def <<= [A](f:  BuildStep[Throwable, A]) =  f match {
      case Continue(v) => v
      case Failure(e) => e
    }

    implicit val applicative = applicativeBuilder[Throwable]

    implicit def build[A,B](s: BuildStep[Throwable,A => B])=new SmartBuilder(s)
    implicit def smartify[A,B,C](target: Curryable[A,B,C])(implicit applicative: Applicative[({type f[x] = BuildStep[Throwable, x]})#f]) = build(applicative.unit(target.curried))

  }