Add or combinator to Validated. Closes #1447

core/src/main/scala/cats/data/Validated.scala

@@ -44,6 +44,7 @@ sealed abstract class Validated[+E, +A] extends Product with Serializable {
 
   /**
    * Return this if it is Valid, or else fall back to the given default.
+   * The functionality is similar to that of [[or]] except for failure accumulation.
    */
   def orElse[EE, AA >: A](default: => Validated[EE, AA]): Validated[EE, AA] =
     this match {
@@ -218,6 +219,18 @@ sealed abstract class Validated[+E, +A] extends Product with Serializable {
    */
   def ensure[EE >: E](onFailure: => EE)(f: A => Boolean): Validated[EE, A] =
     fold(_ => this, a => if (f(a)) this else Validated.invalid(onFailure))
+
+  /**
+    * If `this` is valid return `this`, otherwise if `that` is valid return `that`, otherwise combine the failures.
+    * This is similar to [[orElse]] except that here failures are accumulated.
+    */
+  def or[EE >: E, AA >: A](that: => Validated[EE, AA])(implicit EE: Semigroup[EE]): Validated[EE, AA] = this match {
+    case v @ Valid(_) => v
+    case Invalid(e) => that match {
+      case v @ Valid(_) => v
+      case Invalid(ee) => Invalid(EE.combine(e, ee))
+    }
+  }
 }
 
 object Validated extends ValidatedInstances with ValidatedFunctions{