From abd54ff91c00460673c0ac98a35346be62524a95 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Piotr=20Gawry=C5=9B?= <pgawrys2@gmail.com>
Date: Thu, 24 May 2018 01:36:19 +0200
Subject: [PATCH] Add .parFlatTraverse and .parFlatSequence syntax (#2256)

* Add .parFlatTraverse and .parFlatSequence syntax

* Fix typo in catsSyntaxParallelFlatTraverse

* Binary compability
---
 core/src/main/scala/cats/syntax/all.scala       |  3 ++-
 core/src/main/scala/cats/syntax/parallel.scala  | 17 +++++++++++++++++
 .../test/scala/cats/tests/ParallelSuite.scala   | 14 ++++++++++++++
 .../src/test/scala/cats/tests/SyntaxSuite.scala |  9 +++++++++
 4 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/core/src/main/scala/cats/syntax/all.scala b/core/src/main/scala/cats/syntax/all.scala
index 87c2497f04..9dd4f81989 100644
--- a/core/src/main/scala/cats/syntax/all.scala
+++ b/core/src/main/scala/cats/syntax/all.scala
@@ -60,5 +60,6 @@ trait AllSyntaxBinCompat0
     with TrySyntax
 
 trait AllSyntaxBinCompat1
-    extends FlatMapOptionSyntax
+  extends FlatMapOptionSyntax
     with NestedSyntax
+    with ParallelFlatSyntax
diff --git a/core/src/main/scala/cats/syntax/parallel.scala b/core/src/main/scala/cats/syntax/parallel.scala
index 62be5e7915..02b6bf8e70 100644
--- a/core/src/main/scala/cats/syntax/parallel.scala
+++ b/core/src/main/scala/cats/syntax/parallel.scala
@@ -13,20 +13,37 @@ trait ParallelSyntax extends TupleParallelSyntax {
     new ParallelApOps[M, A](ma)
 }
 
+trait ParallelFlatSyntax {
+  implicit final def catsSyntaxParallelFlatTraverse[T[_]: Traverse: FlatMap, A]
+  (ta: T[A]): ParallelFlatTraversableOps[T, A] = new ParallelFlatTraversableOps[T, A](ta)
+
+  implicit final def catsSyntaxParallelFlatSequence[T[_]: Traverse: FlatMap, M[_]: Monad, A]
+  (tmta: T[M[T[A]]]): ParallelFlatSequenceOps[T, M, A] = new ParallelFlatSequenceOps[T, M, A](tmta)
+}
 
 final class ParallelTraversableOps[T[_], A](val ta: T[A]) extends AnyVal {
 
   def parTraverse[M[_]: Monad, F[_], B]
   (f: A => M[B])(implicit T: Traverse[T], P: Parallel[M, F]): M[T[B]] =
     Parallel.parTraverse(ta)(f)
+}
 
+final class ParallelFlatTraversableOps[T[_], A](val ta: T[A]) extends AnyVal {
+  def parFlatTraverse[M[_]: Monad, F[_], B]
+  (f: A => M[T[B]])(implicit T0: Traverse[T], T1 : FlatMap[T], P: Parallel[M, F]): M[T[B]] =
+    Parallel.parFlatTraverse(ta)(f)
 }
 
 final class ParallelSequenceOps[T[_], M[_], A](val tma: T[M[A]]) extends AnyVal {
   def parSequence[F[_]]
   (implicit M: Monad[M], T: Traverse[T], P: Parallel[M, F]): M[T[A]] =
     Parallel.parSequence(tma)
+}
 
+final class ParallelFlatSequenceOps[T[_], M[_], A](val tmta: T[M[T[A]]]) extends AnyVal {
+  def parFlatSequence[F[_]]
+  (implicit M: Monad[M], T0: Traverse[T], T1 : FlatMap[T], P: Parallel[M, F]): M[T[A]] =
+    Parallel.parFlatSequence(tmta)
 }
 
 final class ParallelApOps[M[_], A](val ma: M[A]) extends AnyVal {
diff --git a/tests/src/test/scala/cats/tests/ParallelSuite.scala b/tests/src/test/scala/cats/tests/ParallelSuite.scala
index cf393fdd5a..f9b6434e93 100644
--- a/tests/src/test/scala/cats/tests/ParallelSuite.scala
+++ b/tests/src/test/scala/cats/tests/ParallelSuite.scala
@@ -79,6 +79,20 @@ class ParallelSuite extends CatsSuite with ApplicativeErrorForEitherTest {
     }
   }
 
+  test("ParFlatSequence syntax should be equivalent to Parallel.parFlatSequence") {
+    forAll { es: List[Either[String, List[Int]]] =>
+      es.parFlatSequence should === (Parallel.parFlatSequence(es))
+    }
+  }
+
+  test("ParFlatTraverse syntax should be equivalent to Parallel.parFlatTraverse") {
+    forAll { es: List[Either[String, Int]] =>
+      val f: Int => List[Int] = i => List(i, i + 1)
+      Parallel.parFlatTraverse(es)(e => e.map(f)) should
+        === (es.parFlatTraverse(e => e.map(f)))
+    }
+  }
+
   test("ParNonEmptyFlatTraverse should be equivalent to parNonEmptyTraverse map flatten") {
     forAll { es: NonEmptyList[Either[String, Int]] =>
       val f: Int => NonEmptyList[Int] = i => NonEmptyList.of(i, i + 1)
diff --git a/tests/src/test/scala/cats/tests/SyntaxSuite.scala b/tests/src/test/scala/cats/tests/SyntaxSuite.scala
index 5dc48aa6c0..8da279c4fe 100644
--- a/tests/src/test/scala/cats/tests/SyntaxSuite.scala
+++ b/tests/src/test/scala/cats/tests/SyntaxSuite.scala
@@ -180,6 +180,15 @@ object SyntaxSuite extends AllInstances with AllSyntax with AllSyntaxBinCompat1
     val ma2: M[A] = ma <& mb
   }
 
+  def testParallelFlat[M[_]: Monad, F[_], T[_]: Traverse: FlatMap, A, B](implicit P: Parallel[M, F]): Unit = {
+    val ta = mock[T[A]]
+    val f = mock[A => M[T[B]]]
+    val mtb = ta.parFlatTraverse(f)
+
+    val tmta = mock[T[M[T[A]]]]
+    val mta = tmta.parFlatSequence
+  }
+
   def testParallelTuple[M[_]: Monad, F[_], A, B, C, Z](implicit P: NonEmptyParallel[M, F]) = {
     val tfabc = mock[(M[A], M[B], M[C])]
     val fa = mock[M[A]]