CODEWITHSUNDEEP
scalavalidationscalaz
silverberry
silverberry

Reputation: 842

Scalaz: Map of ValidationNel to ValidationNel of Map

How do I convert a

val source: Map[MyKeyType, ValidationNel[MyErrorType, MyValueType]]

to

val target: ValidationNel[MyErrorType, Map[MyKeyType, MyValueType]]

while capturing all validation errors?

Upvotes: 3

Views: 144

Answers (2)

Travis Brown
Travis Brown

Reputation: 139058

You can use sequence to turn a type F[G[A]] inside out (i.e., into a G[F[A]]) if you have two things: an Applicative instance for G and a Traverse instance for F. In this case Scalaz provides both off the shelf, so you can just write source.sequenceU (where the U part indicates that this is a method that uses the Unapply trick to help out Scala's type inference system).

For example:

scala> println(Map("a" -> 1.successNel, "b" -> 2.successNel).sequenceU)
Success(Map(a -> 1, b -> 2))

scala> println(Map("a" -> 1.successNel, "b" -> "BAD".failureNel).sequenceU)
Failure(NonEmptyList(BAD))

And errors will be accumulated as expected.

Upvotes: 3

Noah
Noah

Reputation: 13959

You want sequenceU:

val target = source.sequenceU

Upvotes: 2

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