Add :: method to NonEmptyList

typelevel · Jul 27, 2016 · cfdd085 · cfdd085
1 parent c8fcaf0
commit cfdd085
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diff --git a/core/src/main/scala/cats/data/NonEmptyList.scala b/core/src/main/scala/cats/data/NonEmptyList.scala
@@ -30,6 +30,8 @@ final case class NonEmptyList[A](head: A, tail: List[A]) {
   def flatMap[B](f: A => NonEmptyList[B]): NonEmptyList[B] =
     f(head) ++ tail.flatMap(f andThen (_.toList))
 
+  def ::(a: A): NonEmptyList[A] = NonEmptyList(a, head :: tail)
+
   /**
    * remove elements not matching the predicate
    */

diff --git a/tests/src/test/scala/cats/tests/NonEmptyListTests.scala b/tests/src/test/scala/cats/tests/NonEmptyListTests.scala
@@ -172,6 +172,12 @@ class NonEmptyListTests extends CatsSuite {
       NonEmptyList.fromListUnsafe(List.empty[Int])
     }
   }
+
+  test(":: consistent with List") {
+    forAll { (nel: NonEmptyList[Int], i: Int) =>
+      (i :: nel).toList should === (i :: nel.toList)
+    }
+  }
 }
 
 class ReducibleNonEmptyListCheck extends ReducibleCheck[NonEmptyList]("NonEmptyList") {