Scalaz：析取序列到析取序列

Question

I am trying to transform List[\\/[String, Int]] to \\/[String, List[Int]] . All solutions that I was able to find point out to the usage of sequenceU . I was not able to return \\/[String, List[Int]] , since sequenceU returns type GM[List[GA]] :

def f(x: Int): \/[String, Int] = if (x > 0) x.right[String] else "failure".left[Int]
val result: G.M[List[G.A]] = List(3, 4, 5).map(f).sequenceU

What am I doing wrong with sequenceU ? How it should be used to get \\/[String, List[Int]] ?

Answer 1

Just remove the type ascription:

scala> val result = List(3, 4, 5).map(f).sequenceU
result: scalaz.\/[String,List[Int]] = \/-(List(3, 4, 5))