Enable breakout in functions nonEmptyTraverse_ and nonEmptySequence_ (#…

…3545)

* Enable breakout in functions nonEmptyTraverse_ and nonEmptySequence_

* f => f andThen G.void

core/src/main/scala/cats/Reducible.scala

@@ -181,8 +181,10 @@ import scala.annotation.implicitNotFound
    * available for `G` and want to take advantage of short-circuiting
    * the traversal.
    */
-  def nonEmptyTraverse_[G[_], A, B](fa: F[A])(f: A => G[B])(implicit G: Apply[G]): G[Unit] =
-    G.void(reduceLeftTo(fa)(f)((x, y) => G.map2(x, f(y))((_, b) => b)))
+  def nonEmptyTraverse_[G[_], A, B](fa: F[A])(f: A => G[B])(implicit G: Apply[G]): G[Unit] = {
+    val f1 = f.andThen(G.void)
+    reduceRightTo(fa)(f1)((x, y) => G.map2Eval(f1(x), y)((_, b) => b)).value
+  }
 
   /**
    * Sequence `F[G[A]]` using `Apply[G]`.
@@ -192,7 +194,7 @@ import scala.annotation.implicitNotFound
    * [[nonEmptyTraverse_]] documentation for a description of the differences.
    */
   def nonEmptySequence_[G[_], A](fga: F[G[A]])(implicit G: Apply[G]): G[Unit] =
-    G.void(reduceLeft(fga)((x, y) => G.map2(x, y)((_, b) => b)))
+    nonEmptyTraverse_(fga)(identity)
 
   def toNonEmptyList[A](fa: F[A]): NonEmptyList[A] =
     reduceRightTo(fa)(a => NonEmptyList(a, Nil)) { (a, lnel) =>

tests/src/test/scala/cats/tests/ReducibleSuite.scala

@@ -92,7 +92,16 @@ class ReducibleSuiteAdditional extends CatsSuite {
 
     notAllEven.reduceMapA { a => out += a; if (a % 2 == 0) Some(a) else None }
 
-    assert(out.toList === (List(2, 4, 6, 9)))
+    assert(out.toList === List(2, 4, 6, 9))
+  }
+
+  test("Reducible[NonEmptyList].nonEmptyTraverse_ can breakout") {
+    val notAllEven = NonEmptyList.of(2, 4, 6, 9, 10, 12, 14)
+    val out = mutable.ListBuffer[Int]()
+
+    notAllEven.nonEmptyTraverse_ { a => out += a; if (a % 2 == 0) Some(a) else None }
+
+    assert(out.toList === List(2, 4, 6, 9))
   }
 
   // A simple non-empty stream with lazy `foldRight` and `reduceRightTo` implementations.