Adds 'sequence' for Map[A, ErrorOr[B]]

src/main/scala/lenthall/validation/ErrorOr.scala

@@ -3,6 +3,8 @@ package lenthall.validation
 import cats.data.Validated.{Invalid, Valid}
 import cats.data.{NonEmptyList, Validated}
 import cats.syntax.apply._
+import cats.syntax.traverse._
+import cats.instances.list._
 
 object ErrorOr {
   type ErrorOr[A] = Validated[NonEmptyList[String], A]
@@ -16,11 +18,20 @@ object ErrorOr {
     def flatMap[B](f: A => ErrorOr[B]): ErrorOr[B] = {
       fa match {
         case Valid(v) => f(v)
-        case i@Invalid(_) => i
+        case i @ Invalid(_) => i
       }
     }
   }
 
+  implicit class MapErrorOrRhs[A, B](val m: Map[A, ErrorOr[B]]) extends AnyVal {
+    def sequence: ErrorOr[Map[A, B]] = m.traverseValues(identity)
+  }
+
+  implicit class MapTraversal[A, B](val m: Map[A, B]) extends AnyVal {
+    def traverse[C,D](f: ((A,B)) => ErrorOr[(C,D)]): ErrorOr[Map[C,D]] = m.toList.traverse(f).map(_.toMap)
+    def traverseValues[C](f: B => ErrorOr[C]): ErrorOr[Map[A,C]] = m.traverse { case (a, b) => f(b).map(c => (a,c)) }
+  }
+
   // Note! See the bottom of this file for a generator function for 2 through 22 of these near-identical ShortCircuitingFlatMapTupleNs...
 
   implicit class ShortCircuitingFlatMapTuple1[A](val t1: Tuple1[ErrorOr[A]]) extends AnyVal {

src/test/scala/lenthall/validation/ErrorOrSpec.scala

@@ -1,5 +1,7 @@
 package lenthall.validation
 
+import cats.data.NonEmptyList
+import cats.data.Validated.{Invalid, Valid}
 import cats.data.Validated.Valid
 import cats.syntax.validated._
 import lenthall.validation.ErrorOr._
@@ -25,6 +27,20 @@ class ErrorOrSpec extends FlatSpec with Matchers {
     errorMapped should be("hello".invalidNel)
   }
 
+  it should "sequence a map of valid ErrorOrs" in {
+    val eo1 = Valid("good1")
+    val eo2 = Valid("good2")
+    Map(1 -> eo1, 2 -> eo2).sequence should be(Valid(Map(1 -> "good1", 2 -> "good2")))
+  }
+
+  it should "sequence a map of mixed ErrorOrs" in {
+    val eo1 = Valid("good1")
+    val eo2 = "bad2".invalidNel
+    val eo3 = Valid("good3")
+    val eo4 = "bad4".invalidNel
+    Map(1 -> eo1, 2 -> eo2, 3 -> eo3, 4 -> eo4).sequence should be(Invalid(NonEmptyList("bad2", List("bad4"))))
+  }
+
   val DivBy0Error: String = "Divide by 0!"
   def errorOrDiv(v1: Int, v2: Int): ErrorOr[Double] = if (v2 != 0) { Valid(v1.toDouble / v2.toDouble) } else { DivBy0Error.invalidNel }
   def errorOrDiv(v1: Double, v2: Int): ErrorOr[Double] = if (v2 != 0) { Valid(v1.toDouble / v2.toDouble) } else { DivBy0Error.invalidNel }