[英]List of Kleisli to Kleisli of list
I was wondering if there is a way to turn List[Kleisli[Option, Int, Int]]
to Kleisli[Option, Int, List[Int]]
. 我想知道是否有办法将
List[Kleisli[Option, Int, Int]]
为Kleisli[Option, Int, List[Int]]
。
In particular I have the list of kleisli formed like this: 特别是我有像这样形成的kleisli列表:
def k(a: String) = Kleisli[Option, Int, Int](m => Some(a.length * m))
val kList = List("hi", "hello").map(k)
What I do is the following 我所做的是以下内容
Kleisli[Option, Int, List[Int]](m => kList.map(_.run(m)).sequence)
which is very messy, not expressive and requires a lot of manual work. 这是非常混乱,没有表现力,需要大量的手工工作。
Is there a better way? 有没有更好的办法?
Yes, you can use traverse
which does just that. 是的,你可以使用
traverse
来做到这一点。 If you're using cats
<= 0.9.0 you can use the following code: 如果你使用的
cats
<= 0.9.0,你可以使用以下代码:
import cats.data._
import cats.instances.list._
import cats.instances.option._
import cats.syntax.traverse._
// ...
def k(a: String) = Kleisli[Option, Int, Int](m => Some(a.length * m))
val result: Kleisli[Option, Int, List[Int] = List("hi", "hello").traverseU(k)
If you're using Scala 2.11.9+, by adding scalacOptions += "-Ypartial-unification"
to your build.sbt
file, you can just use traverse
in place of traverseU
. 如果您正在使用Scala 2.11.9
scalacOptions += "-Ypartial-unification"
,通过在build.sbt
文件中添加scalacOptions += "-Ypartial-unification"
,您可以使用traverse
代替traverseU
。 Also, starting from version 1.0.0, traverseU
and sequenceU
will no longer exist. 此外,从版本1.0.0开始,
traverseU
和sequenceU
将不再存在。
Note that, if you're using Scala < 2.11.9 but >= 2.10.6 you can still enable partial unification by adding this plugin to your build. 请注意,如果您使用Scala <2.11.9但> = 2.10.6,您仍然可以通过将此插件添加到构建中来启用部分统一。
The simplest you can do is to have partial-unification
enabled and using traverse
: 您最简单的方法是启用
partial-unification
并使用traverse
:
import cats.implicits._
List("hi", "hello").traverse(k)
This is the same as running sequence
on your kList
, as traverse
is equivalent to map
and then sequence
. 这与
kList
上的运行sequence
相同,因为traverse
相当于map
,然后是sequence
。
The easiest way to enable partial-unification
, is to add the sbt-partial-unification
plugin . 启用
partial-unification
的最简单方法是添加sbt-partial-unification
插件 。
If you're on Scala 2.11.9 or newer, you can also simply add the compiler flag: 如果你使用的是Scala 2.11.9或更高版本,你也可以简单地添加编译器标志:
scalacOptions += "-Ypartial-unification"
We from the cats
team strongly encourage you to have this flag on at all times when using cats, as it makes everything just a lot easier. 来自
cats
队的我们强烈建议您在使用猫时始终使用此标志,因为它使一切变得更加容易。
Using TraverseOps.sequence
we can transform List[A[B]]
to A[List[B]]
, where 使用
TraverseOps.sequence
我们可以将List[A[B]]
变换为A[List[B]]
,其中
A = ({type λ[α] = Kleisli[Option, Int, α]})#λ
B = Int
So the answer is: 所以答案是:
def transform(x: List[Kleisli[Option, Int, Int]]) =
x.sequence[({type λ[α] = Kleisli[Option, Int, α]})#λ, Int]
Following code is complete solution: 以下代码是完整解决方案:
import scalaz._
import Scalaz._
import scalaz.Kleisli._
def transform(x: List[Kleisli[Option, Int, Int]]) = x.sequence[({type λ[α] = Kleisli[Option, Int, α]})#λ, Int]
def k(a: String) = Kleisli[Option, Int, Int](m => Some(a.length * m))
val kList = List("hi", "hello").map(k)
val res = transform(kList)
res.run(10)
https://scastie.scala-lang.org/2uZvWWb1ScOHNA55QOcWQA https://scastie.scala-lang.org/2uZvWWb1ScOHNA55QOcWQA
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