[英]Scalaz Kleisli usage benefits
In scalaz Kleisli[M[_], A, B]
is a wrapper of A => M[B]
, which allows composition of such functions. 在scalaz
Kleisli[M[_], A, B]
是A => M[B]
的包装,它允许组合这些函数。 For instance, if M[_]
is monad I can compose Kleisli[M, A, B]
and Kleisli[M, B, C]
with >=>
to get Kleisli[M, A, C]
. 例如,如果
M[_]
是monad,我可以用>=>
组成Kleisli[M, A, B]
和Kleisli[M, B, C]
以得到Kleisli[M, A, C]
。
In a nutshell, Kleisli
provides fancy andThens
depending on M
. 简而言之,
Kleisli
提供看中andThens
根据M
。 Is it correct ? 这是正确的吗 ? Are there other benefits of using
Kleisli
? 使用
Kleisli
还有其他好处吗?
Here are two benefits as examples—I'm sure you could come up with others. 这有两个好处作为例子 - 我相信你可以拿出其他人。
First, it can be useful to abstract over different arrows, such as Kleisli[M, ?, ?]
and ? => ?
首先,抽象不同的箭头是有用的,例如
Kleisli[M, ?, ?]
和? => ?
? => ?
. 。 For example, I can write a generic function that will apply an endomorphism a certain number of times.
例如,我可以编写一个通用函数,它将内部结构应用一定次数。
def applyX10[Arr[_, _]: Category, A](f: Arr[A, A]) =
List.fill(10)(Endomorphic(f)).suml
Now I can use this on eg Int => Int
or Kleisli[Option, Int, Int]
: 现在我可以在例如
Int => Int
或Kleisli[Option, Int, Int]
:
val f = (_: Int) + 1
val k = Kleisli.kleisli[Option, Int, Int] {
case i if i % 2 == 0 => Some(i * 3)
case _ => None
}
And then: 然后:
scala> applyX10(f).run(1)
res0: Int = 11
scala> applyX10[=?>, Int](k).run(2)
res1: Option[Int] = Some(118098)
(Note that A =?> B
is just an alias for Kleisli[Option, A, B]
.) (注意
A =?> B
只是Kleisli[Option, A, B]
的别名。)
Second, the fact that Kleisli[F, ?, ?]
has a monad instance if F
does can also be useful. 其次,如果
F
确实如此, Kleisli[F, ?, ?]
具有monad实例的事实也是有用的。 See for example my answer here for a demonstration of how you can use monadic composition with ReaderT
, which is just an alias for Kleisli
. 例如,请参阅我的答案 ,以演示如何使用
ReaderT
组合,这只是Kleisli
的别名。
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