SemigroupK sum: F[A], F[B] => F[A Either B] (#3124)

* #3112 adding implementation * #3112 added documentation with example * adding pk044 to AUTHORS.md * formatting * fixed doctest * fixed doctest * used different type in example
typelevel · Nov 5, 2019 · 6d191a5 · 6d191a5
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diff --git a/AUTHORS.md b/AUTHORS.md
@@ -191,6 +191,7 @@ possible:
  * Paulo "JCranky" Siqueira
  * Pavel Chlupacek
  * Pavkin Vladimir
+ * Paweł Kiersznowski
  * Paweł Lipski
  * Pepe García
  * Pere Villega

diff --git a/core/src/main/scala/cats/SemigroupK.scala b/core/src/main/scala/cats/SemigroupK.scala
@@ -68,6 +68,20 @@ import cats.data.Ior
  new ComposedSemigroupK[F, G] {
  val F = self
  }
+
+ /**
+ * Combines `F[A]` and `F[B]` into a `F[Either[A,B]]]`.
+ *
+ * Example:
+ * {{{
+ * scala> import cats.SemigroupK
+ * scala> import cats.data.NonEmptyList
+ * scala> SemigroupK[NonEmptyList].sum(NonEmptyList.one("abc"), NonEmptyList.one(2))
+ * res0: NonEmptyList[Either[String,Int]] = NonEmptyList(Left(abc), Right(2))
+ * }}}
+ */
+ def sum[A, B](fa: F[A], fb: F[B])(implicit F: Functor[F]): F[Either[A, B]] =
+ combineK(F.map(fa)(Left(_)), F.map(fb)(Right(_)))
 }
 
 object SemigroupK {