Created
September 18, 2012 16:03
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Kleisli composition
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| scala> import scalaz._, Scalaz._ | |
| import scalaz._ | |
| import Scalaz._ | |
| scala> def str(x: Int): Option[String] = Some(x.toString) | |
| str: (x: Int)Option[String] | |
| scala> def toInt(x: String): Option[Int] = Some(x.toInt) | |
| toInt: (x: String)Option[Int] | |
| scala> def double(x: Int): Option[Double] = Some(x * 2) | |
| double: (x: Int)Option[Double] | |
| scala> val arrows = Kleisli(str) >=> Kleisli(toInt) >=> Kleisli(double) | |
| arrows: scalaz.Kleisli[Option,Int,Double] = scalaz.KleisliFunctions$$anon$18@58741a85 | |
| scala> arrows(6) | |
| res0: Option[Double] = Some(12.0) | |
| scala> val andThen = Kleisli(str) andThen Kleisli(toInt) andThen Kleisli(double) | |
| andThen: scalaz.Kleisli[Option,Int,Double] = scalaz.KleisliFunctions$$anon$18@3146d556 | |
| scala> andThen(10) | |
| res1: Option[Double] = Some(20.0) | |
| scala> 1.some.flatMap(arrows) | |
| res2: Option[Double] = Some(2.0) | |
| scala> 1.some.map(arrows) | |
| res3: Option[Option[Double]] = Some(Some(2.0)) |
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andThen and arrows in this case are the same, the arrows are an alternative.