I'm using the cats
lib for this.
It's easy enough to combine two lists using their applicative functor instance (or Cartesian
, to be precise):
import cats._
import cats.implicits._
(List(23, 4), List(55, 56)).mapN(_ + _)
>> List(78, 79, 59, 60)
However, I can't seem to be able to do the same with two functions:
val strLength: String => Int = _.length
(strLength, strLength).mapN(_ + _)
>> value mapN is not a member of (String => Int, String => Int)
It does work if I do some of the implicit conversions explicitly, and if I create a type alias to give the compiler a hand:
type F[A] = Function1[String, A]
val doubleStrLength = catsSyntaxTuple2Cartesian[F, Int, Int]((strLength, strLength)).mapN(_ + _)
doubleStrLength("hello")
>> 10
Is there an easier way to do this? Seems excessively verbose
Edit: I create a worksheet here if you wanna play with it: https://scastie.scala-lang.org/dcastro/QhnD8gwEQEyfnr14g34d9g/2
This only works if you have partial-unification
enabled. The easiest way to do so, is to add the sbt-partial-unification
plugin .
If you're on Scala 2.11.9 or newer, you can also simply add the compiler flag:
scalacOptions += "-Ypartial-unification"
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.