使用scalaz Monad的示例

Question

任何人都可以举一个使用scalaz Monad进行简单但非平凡且实用的任务的例子吗？

Answer 1

scalaz.Monad , and the family of related type classes, abstract some common functionality across a vast array of types. Scalaz provides general purpose functions that work for any Monad ; and you can write your own functions in the same fashion.

Without this abstraction, you are forced to write these functions for each new monadic type that you encounter, eg List , Parser , Option . This gets tedious!

Here are examples of a few provided functions, working with a couple monadic types. My favorite is sequence :

scala> 1.pure[Option].pure[Option]
res1: Option[Option[Int]] = Some(Some(1))

scala> res1.join
res2: Option[Int] = Some(1)

scala> List(1.some, 2.some).sequence
res3: Option[List[Int]] = Some(List(1, 2))

scala> List(1.some, none[Int]).sequence
res4: Option[List[Int]] = None

scala> List(1.pure[Function0])      
res5: List[() => Int] = List(<function0>)

scala> res5.sequence
res6: () => List[Int] = <function0>

scala> res6()
res7: List[Int] = List(1)

scala> true.some ifM(none[Int], 1.some)
res8: Option[Int] = None

scala> false.some ifM(none[Int], 1.some)
res9: Option[Int] = Some(1)