From e0a572f93d605afe1b901bcae9a4ae7dcf7ec3d3 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 10:52:55 +0100
Subject: [PATCH 01/16] Add ifA to Apply

---
 core/src/main/scala/cats/Apply.scala        | 32 +++++++++++++++++++++
 core/src/main/scala/cats/syntax/apply.scala |  5 +---
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/core/src/main/scala/cats/Apply.scala b/core/src/main/scala/cats/Apply.scala
index 3a43f93a43..e1e3265153 100644
--- a/core/src/main/scala/cats/Apply.scala
+++ b/core/src/main/scala/cats/Apply.scala
@@ -214,6 +214,38 @@ trait Apply[F[_]] extends Functor[F] with InvariantSemigroupal[F] with ApplyArit
       val G = Apply[G]
     }
 
+  /**
+   * An `if-then-else` lifted into the `F` context.
+   * This function combines the effects of the `fcond` condition and of the two branches,
+   * in the order in which they are given.
+   *
+   * The value of the result is, depending on the value of the condition,
+   * the value of the first argument, or the value of the second argument.
+   *
+   * Example:
+   * {{{
+   * scala> import cats.implicits._
+   *
+   * scala> val b1: Option[Boolean] = Some(true)
+   * scala> val asInt1: Option[Int] = Apply[Option].ifA(b1)(Some(1), Some(0))
+   * scala> asInt1.get
+   * res0: Int = 1
+   *
+   * scala> val b2: Option[Boolean] = Some(false)
+   * scala> val asInt2: Option[Int] = Apply[Option].ifA(b2)(Some(1), Some(0))
+   * scala> asInt2.get
+   * res1: Int = 0
+   *
+   * scala> val b3: Option[Boolean] = Some(true)
+   * scala> val asInt3: Option[Int] = Apply[Option].ifA(b3)(Some(1), None)
+   * asInt2: Option[Int] = None
+   *
+   * }}}
+   */
+  def ifA[A](fcond: F[Boolean])(ifTrue: F[A], ifFalse: F[A]): F[A] = {
+    def ite(b: Boolean)(ifTrue: A, ifFalse: A) = if (b) ifTrue else ifFalse
+    ap2(map(fcond)(ite))(ifTrue, ifFalse)
+  }
 }
 
 object Apply {
diff --git a/core/src/main/scala/cats/syntax/apply.scala b/core/src/main/scala/cats/syntax/apply.scala
index b11501c15a..3f9f4b7763 100644
--- a/core/src/main/scala/cats/syntax/apply.scala
+++ b/core/src/main/scala/cats/syntax/apply.scala
@@ -49,10 +49,7 @@ final class IfApplyOps[F[_]](private val fcond: F[Boolean]) extends AnyVal {
    *
    * }}}
    */
-  def ifA[A](ifTrue: F[A], ifFalse: F[A])(implicit F: Apply[F]): F[A] = {
-    def ite(b: Boolean)(ifTrue: A, ifFalse: A) = if (b) ifTrue else ifFalse
-    F.ap2(F.map(fcond)(ite))(ifTrue, ifFalse)
-  }
+  def ifA[A](ifTrue: F[A], ifFalse: F[A])(implicit F: Apply[F]): F[A] = F.ifA(fcond)(ifTrue, ifFalse)
 }
 
 final class ApplyOps[F[_], A](private val fa: F[A]) extends AnyVal {

From 0655be35904057a541e8e85c4103d70a798584c0 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 11:11:08 +0100
Subject: [PATCH 02/16] Add sequenceFilter to TraverseFilter

---
 core/src/main/scala/cats/TraverseFilter.scala        | 11 +++++++++++
 core/src/main/scala/cats/syntax/traverseFilter.scala |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/core/src/main/scala/cats/TraverseFilter.scala b/core/src/main/scala/cats/TraverseFilter.scala
index ea2848de63..b4e19c50f5 100644
--- a/core/src/main/scala/cats/TraverseFilter.scala
+++ b/core/src/main/scala/cats/TraverseFilter.scala
@@ -34,6 +34,17 @@ trait TraverseFilter[F[_]] extends FunctorFilter[F] {
    */
   def traverseFilter[G[_], A, B](fa: F[A])(f: A => G[Option[B]])(implicit G: Applicative[G]): G[F[B]]
 
+  /**
+   * {{{
+   * scala> import cats.implicits._
+   * scala> val a: List[Either[String, Option[Int]]] = List(Right(Some(1)), Right(Some(5)), Right(Some(3)))
+   * scala> val b: Either[String, List[Int]] = TraverseFilter[List].sequenceFilter(a)
+   * b: Either[String, List[Int]] = Right(List(1, 5, 3))
+   * }}}
+   * */
+  def sequenceFilter[G[_], A](fgoa: F[G[Option[A]]])(implicit G: Applicative[G]): G[F[A]] =
+    traverseFilter(fgoa)(identity)
+
   /**
    *
    * Filter values inside a `G` context.
diff --git a/core/src/main/scala/cats/syntax/traverseFilter.scala b/core/src/main/scala/cats/syntax/traverseFilter.scala
index 9a00baba89..36c57b62a7 100644
--- a/core/src/main/scala/cats/syntax/traverseFilter.scala
+++ b/core/src/main/scala/cats/syntax/traverseFilter.scala
@@ -18,5 +18,5 @@ final class SequenceFilterOps[F[_], G[_], A](private val fgoa: F[G[Option[A]]])
    * b: Either[String, List[Int]] = Right(List(1, 5, 3))
    * }}}
    * */
-  def sequenceFilter(implicit F: TraverseFilter[F], G: Applicative[G]): G[F[A]] = F.traverseFilter(fgoa)(identity)
+  def sequenceFilter(implicit F: TraverseFilter[F], G: Applicative[G]): G[F[A]] = F.sequenceFilter(fgoa)
 }

From a11a61cf5b0eda14bf8d98b3d6e1f35c4a48b10b Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 12:52:25 +0100
Subject: [PATCH 03/16] Add count to UnorderedFoldable

---
 .../main/scala/cats/UnorderedFoldable.scala   | 22 ++++++++++++++++++-
 .../scala/cats/syntax/unorderedFoldable.scala |  4 +---
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/core/src/main/scala/cats/UnorderedFoldable.scala b/core/src/main/scala/cats/UnorderedFoldable.scala
index 4336908d1f..0e3929f019 100644
--- a/core/src/main/scala/cats/UnorderedFoldable.scala
+++ b/core/src/main/scala/cats/UnorderedFoldable.scala
@@ -1,8 +1,8 @@
 package cats
 
+import cats.instances.long._
 import cats.kernel.CommutativeMonoid
 import simulacrum.typeclass
-import cats.instances.long._
 
 /**
  * `UnorderedFoldable` is like a `Foldable` for unordered containers.
@@ -48,6 +48,26 @@ import cats.instances.long._
    * Note: will not terminate for infinite-sized collections.
    */
   def size[A](fa: F[A]): Long = unorderedFoldMap(fa)(_ => 1L)
+
+  /**
+   * Count the number of elements in the structure that satisfy the given predicate.
+   *
+   * For example:
+   * {{{
+   * scala> import cats.implicits._
+   * scala> val map1 = Map[Int, String]()
+   * scala> val p1: String => Boolean = _.length > 0
+   * scala> UnorderedFoldable[Map[Int, *]].count(map1)(p1)
+   * res0: Long = 0
+   *
+   * scala> val map2 = Map(1 -> "hello", 2 -> "world", 3 -> "!")
+   * scala> val p2: String => Boolean = _.length > 1
+   * scala> UnorderedFoldable[Map[Int, *]].count(map2)(p2)
+   * res1: Long = 2
+   * }}}
+   */
+  def count[A](fa: F[A])(p: A => Boolean): Long =
+    unorderedFoldMap(fa)(a => if (p(a)) 1L else 0L)
 }
 
 object UnorderedFoldable {
diff --git a/core/src/main/scala/cats/syntax/unorderedFoldable.scala b/core/src/main/scala/cats/syntax/unorderedFoldable.scala
index 567780c529..99f2ee1a3f 100644
--- a/core/src/main/scala/cats/syntax/unorderedFoldable.scala
+++ b/core/src/main/scala/cats/syntax/unorderedFoldable.scala
@@ -1,8 +1,6 @@
 package cats
 package syntax
 
-import cats.instances.long._
-
 trait UnorderedFoldableSyntax extends UnorderedFoldable.ToUnorderedFoldableOps {
   implicit final def catsSyntaxUnorderedFoldableOps[F[_]: UnorderedFoldable, A](fa: F[A]): UnorderedFoldableOps[F, A] =
     new UnorderedFoldableOps[F, A](fa)
@@ -28,5 +26,5 @@ final class UnorderedFoldableOps[F[_], A](private val fa: F[A]) extends AnyVal {
    * }}}
    */
   def count(p: A => Boolean)(implicit F: UnorderedFoldable[F]): Long =
-    F.unorderedFoldMap(fa)(a => if (p(a)) 1L else 0L)
+    F.count(fa)(p)
 }

From 155a6631f1d6d187df66ee3e632c1412777d72c8 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 07:21:00 -0600
Subject: [PATCH 04/16] Add fromOption and fromValidated to ApplicativeError

---
 .../main/scala/cats/ApplicativeError.scala    | 45 ++++++++++++++++++-
 .../scala/cats/syntax/applicativeError.scala  | 18 +++-----
 .../main/scala/cats/syntax/validated.scala    |  2 +-
 3 files changed, 51 insertions(+), 14 deletions(-)

diff --git a/core/src/main/scala/cats/ApplicativeError.scala b/core/src/main/scala/cats/ApplicativeError.scala
index ec4ab1bcda..7acd0a0eb5 100644
--- a/core/src/main/scala/cats/ApplicativeError.scala
+++ b/core/src/main/scala/cats/ApplicativeError.scala
@@ -1,6 +1,7 @@
 package cats
 
-import cats.data.EitherT
+import cats.data.{EitherT, Validated}
+import cats.data.Validated.{Invalid, Valid}
 
 import scala.reflect.ClassTag
 import scala.util.{Failure, Success, Try}
@@ -186,6 +187,48 @@ trait ApplicativeError[F[_], E] extends Applicative[F] {
       case Left(e)  => raiseError(e)
     }
 
+  /**
+   * Convert from scala.Option
+   *
+   * Example:
+   * {{{
+   * scala> import cats.implicits._
+   * scala> import cats.ApplicativeError
+   * scala> val F = ApplicativeError[Either[String, *], String]
+   *
+   * scala> F.fromOption(Some(1), "Empty")
+   * res0: scala.Either[String, Int] = Right(1)
+   *
+   * scala> F.fromOption(Option.empty[Int], "Empty")
+   * res1: scala.Either[String, Int] = Left(Empty)
+   * }}}
+   */
+  def fromOption[A](oa: Option[A], ifEmpty: => E): F[A] =
+    oa match {
+      case Some(a) => pure(a)
+      case None    => raiseError(ifEmpty)
+    }
+
+  /**
+   * Convert from cats.data.Validated
+   *
+   * Example:
+   * {{{
+   * scala> import cats.implicits._
+   * scala> import cats.ApplicativeError
+   *
+   * scala> ApplicativeError[Option, Unit].fromValidated(1.valid[Unit])
+   * res0: scala.Option[Int] = Some(1)
+   *
+   * scala> ApplicativeError[Option, Unit].fromValidated(().invalid[Int])
+   * res1: scala.Option[Int] = None
+   * }}}
+   */
+  def fromValidated[A](x: Validated[E, A]): F[A] =
+    x match {
+      case Invalid(e) => raiseError(e)
+      case Valid(a)   => pure(a)
+    }
 }
 
 object ApplicativeError {
diff --git a/core/src/main/scala/cats/syntax/applicativeError.scala b/core/src/main/scala/cats/syntax/applicativeError.scala
index ed58a5cc2a..1e399062aa 100644
--- a/core/src/main/scala/cats/syntax/applicativeError.scala
+++ b/core/src/main/scala/cats/syntax/applicativeError.scala
@@ -1,7 +1,6 @@
 package cats
 package syntax
 
-import cats.data.Validated.{Invalid, Valid}
 import cats.data.{EitherT, Validated}
 
 import scala.reflect.ClassTag
@@ -19,14 +18,15 @@ trait ApplicativeErrorSyntax {
 /**
  * Extension to ApplicativeError in a binary compat way
  */
-trait ApplicativeErrorExtension {
-  implicit final def catsSyntaxApplicativeErrorExtension[F[_], E](
+private[syntax] trait ApplicativeErrorExtension {
+  @deprecated("Use methods on ApplicativeError", "2.1.0-RC1")
+  final def catsSyntaxApplicativeErrorExtension[F[_], E](
     F: ApplicativeError[F, E]
   ): ApplicativeErrorExtensionOps[F, E] =
     new ApplicativeErrorExtensionOps(F)
 }
 
-final class ApplicativeErrorExtensionOps[F[_], E](F: ApplicativeError[F, E]) {
+final private[syntax] class ApplicativeErrorExtensionOps[F[_], E](F: ApplicativeError[F, E]) {
 
   /**
    * Convert from scala.Option
@@ -44,8 +44,7 @@ final class ApplicativeErrorExtensionOps[F[_], E](F: ApplicativeError[F, E]) {
    * res1: scala.Either[String, Int] = Left(Empty)
    * }}}
    */
-  def fromOption[A](oa: Option[A], ifEmpty: => E): F[A] =
-    ApplicativeError.liftFromOption(oa, ifEmpty)(F)
+  private[syntax] def fromOption[A](oa: Option[A], ifEmpty: => E): F[A] = F.fromOption(oa, ifEmpty)
 
   /**
    * Convert from cats.data.Validated
@@ -62,12 +61,7 @@ final class ApplicativeErrorExtensionOps[F[_], E](F: ApplicativeError[F, E]) {
    * res1: scala.Option[Int] = None
    * }}}
    */
-  def fromValidated[A](x: Validated[E, A]): F[A] =
-    x match {
-      case Invalid(e) => F.raiseError(e)
-      case Valid(a)   => F.pure(a)
-    }
-
+  private[syntax] def fromValidated[A](x: Validated[E, A]): F[A] = F.fromValidated(x)
 }
 
 final class ApplicativeErrorIdOps[E](private val e: E) extends AnyVal {
diff --git a/core/src/main/scala/cats/syntax/validated.scala b/core/src/main/scala/cats/syntax/validated.scala
index 29f1b4ad55..758818a36f 100644
--- a/core/src/main/scala/cats/syntax/validated.scala
+++ b/core/src/main/scala/cats/syntax/validated.scala
@@ -21,7 +21,7 @@ trait ValidatedExtensionSyntax {
 
 final class ValidatedExtension[E, A](private val self: Validated[E, A]) extends AnyVal {
   def liftTo[F[_]](implicit F: ApplicativeError[F, _ >: E]): F[A] =
-    new ApplicativeErrorExtensionOps(F).fromValidated(self)
+    F.fromValidated(self)
 }
 
 private[syntax] trait ValidatedSyntaxBincompat0 {

From 7c4302765b1b454e7fc621484f01d3e4ba561e52 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 07:42:18 -0600
Subject: [PATCH 05/16] Add leftTraverse and leftSequence to Bitraverse

---
 core/src/main/scala/cats/Bitraverse.scala     | 48 ++++++++++++++++++-
 .../main/scala/cats/syntax/bitraverse.scala   |  4 +-
 2 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/core/src/main/scala/cats/Bitraverse.scala b/core/src/main/scala/cats/Bitraverse.scala
index dd521cf236..a0439e4137 100644
--- a/core/src/main/scala/cats/Bitraverse.scala
+++ b/core/src/main/scala/cats/Bitraverse.scala
@@ -1,6 +1,6 @@
 package cats
 
-import simulacrum.typeclass
+import simulacrum.{noop, typeclass}
 
 /**
  *  A type class abstracting over types that give rise to two independent [[cats.Traverse]]s.
@@ -61,6 +61,52 @@ import simulacrum.typeclass
 
   override def bimap[A, B, C, D](fab: F[A, B])(f: A => C, g: B => D): F[C, D] =
     bitraverse[Id, A, B, C, D](fab)(f, g)
+
+  /**
+   *  Traverse over the left side of the structure.
+   *  For the right side, use the standard `traverse` from [[cats.Traverse]].
+   *
+   *  Example:
+   *  {{{
+   *  scala> import cats.implicits._
+   *
+   *  scala> val intAndString: (Int, String) = (7, "test")
+   *
+   *  scala> Bitraverse[Tuple2].leftTraverse(intAndString)(i => Option(i).filter(_ > 5))
+   *  res1: Option[(Int, String)] = Some((7,test))
+   *
+   *  scala> Bitraverse[Tuple2].leftTraverse(intAndString)(i => Option(i).filter(_ < 5))
+   *  res2: Option[(Int, String)] = None
+   *  }}}
+   */
+  @noop
+  def leftTraverse[G[_], A, B, C](fab: F[A, B])(f: A => G[C])(implicit G: Applicative[G]): G[F[C, B]] =
+    bitraverse(fab)(f, G.pure(_))
+
+  /**
+   * Sequence the left side of the structure.
+   * For the right side, use the standard `sequence` from [[cats.Traverse]].
+   *
+   * Example:
+   * {{{
+   * scala> import cats.implicits._
+   *
+   * scala> val optionalErrorRight: Either[Option[String], Int] = Either.right(123)
+   * scala> optionalErrorRight.leftSequence
+   * res1: Option[Either[String, Int]] = Some(Right(123))
+   *
+   * scala> val optionalErrorLeftSome: Either[Option[String], Int] = Either.left(Some("something went wrong"))
+   * scala> optionalErrorLeftSome.leftSequence
+   * res2: Option[Either[String, Int]] = Some(Left(something went wrong))
+   *
+   * scala> val optionalErrorLeftNone: Either[Option[String], Int] = Either.left(None)
+   * scala> optionalErrorLeftNone.leftSequence
+   * res3: Option[Either[String,Int]] = None
+   * }}}
+   */
+  @noop
+  def leftSequence[G[_], A, B](fgab: F[G[A], B])(implicit G: Applicative[G]): G[F[A, B]] =
+    bitraverse(fgab)(identity, G.pure(_))
 }
 
 private[cats] trait ComposedBitraverse[F[_, _], G[_, _]]
diff --git a/core/src/main/scala/cats/syntax/bitraverse.scala b/core/src/main/scala/cats/syntax/bitraverse.scala
index 4e72c0b4ee..b09661f267 100644
--- a/core/src/main/scala/cats/syntax/bitraverse.scala
+++ b/core/src/main/scala/cats/syntax/bitraverse.scala
@@ -54,7 +54,7 @@ final private[syntax] class BitraverseOpsBinCompat0[F[_, _], A, B](val fab: F[A,
    *  }}}
    */
   def leftTraverse[G[_], C](f: A => G[C])(implicit F: Bitraverse[F], G: Applicative[G]): G[F[C, B]] =
-    F.bitraverse(fab)(f, G.pure(_))
+    F.leftTraverse[G, A, B, C](fab)(f)
 }
 
 final class LeftNestedBitraverseOps[F[_, _], G[_], A, B](val fgab: F[G[A], B]) extends AnyVal {
@@ -81,5 +81,5 @@ final class LeftNestedBitraverseOps[F[_, _], G[_], A, B](val fgab: F[G[A], B]) e
    * }}}
    */
   def leftSequence(implicit F: Bitraverse[F], G: Applicative[G]): G[F[A, B]] =
-    F.bitraverse(fgab)(identity, G.pure(_))
+    F.leftSequence(fgab)
 }

From d8e00891b7d0348b21b8733b13cfce3efc6cabf7 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 07:46:29 -0600
Subject: [PATCH 06/16] Add @noop to avoid generating redundant syntax methods

---
 core/src/main/scala/cats/Apply.scala             | 4 ++--
 core/src/main/scala/cats/TraverseFilter.scala    | 3 ++-
 core/src/main/scala/cats/UnorderedFoldable.scala | 3 ++-
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/core/src/main/scala/cats/Apply.scala b/core/src/main/scala/cats/Apply.scala
index e1e3265153..fe9308b8c2 100644
--- a/core/src/main/scala/cats/Apply.scala
+++ b/core/src/main/scala/cats/Apply.scala
@@ -1,7 +1,6 @@
 package cats
 
-import simulacrum.typeclass
-import simulacrum.noop
+import simulacrum.{noop, typeclass}
 import cats.data.Ior
 
 /**
@@ -242,6 +241,7 @@ trait Apply[F[_]] extends Functor[F] with InvariantSemigroupal[F] with ApplyArit
    *
    * }}}
    */
+  @noop
   def ifA[A](fcond: F[Boolean])(ifTrue: F[A], ifFalse: F[A]): F[A] = {
     def ite(b: Boolean)(ifTrue: A, ifFalse: A) = if (b) ifTrue else ifFalse
     ap2(map(fcond)(ite))(ifTrue, ifFalse)
diff --git a/core/src/main/scala/cats/TraverseFilter.scala b/core/src/main/scala/cats/TraverseFilter.scala
index b4e19c50f5..0bf3f7330a 100644
--- a/core/src/main/scala/cats/TraverseFilter.scala
+++ b/core/src/main/scala/cats/TraverseFilter.scala
@@ -1,6 +1,6 @@
 package cats
 
-import simulacrum.typeclass
+import simulacrum.{noop, typeclass}
 
 /**
  * `TraverseFilter`, also known as `Witherable`, represents list-like structures
@@ -42,6 +42,7 @@ trait TraverseFilter[F[_]] extends FunctorFilter[F] {
    * b: Either[String, List[Int]] = Right(List(1, 5, 3))
    * }}}
    * */
+  @noop
   def sequenceFilter[G[_], A](fgoa: F[G[Option[A]]])(implicit G: Applicative[G]): G[F[A]] =
     traverseFilter(fgoa)(identity)
 
diff --git a/core/src/main/scala/cats/UnorderedFoldable.scala b/core/src/main/scala/cats/UnorderedFoldable.scala
index 0e3929f019..683575f3e1 100644
--- a/core/src/main/scala/cats/UnorderedFoldable.scala
+++ b/core/src/main/scala/cats/UnorderedFoldable.scala
@@ -2,7 +2,7 @@ package cats
 
 import cats.instances.long._
 import cats.kernel.CommutativeMonoid
-import simulacrum.typeclass
+import simulacrum.{noop, typeclass}
 
 /**
  * `UnorderedFoldable` is like a `Foldable` for unordered containers.
@@ -66,6 +66,7 @@ import simulacrum.typeclass
    * res1: Long = 2
    * }}}
    */
+  @noop
   def count[A](fa: F[A])(p: A => Boolean): Long =
     unorderedFoldMap(fa)(a => if (p(a)) 1L else 0L)
 }

From 731bc13d84321635c8eaa1914421732a1382f46f Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 07:55:04 -0600
Subject: [PATCH 07/16] Add foreverM, iterateForeverM, and untilDefinedM to
 FlatMap

---
 core/src/main/scala/cats/FlatMap.scala        | 46 +++++++++++++++++++
 core/src/main/scala/cats/syntax/flatMap.scala | 22 ++-------
 2 files changed, 49 insertions(+), 19 deletions(-)

diff --git a/core/src/main/scala/cats/FlatMap.scala b/core/src/main/scala/cats/FlatMap.scala
index bb939cca0e..c75ee126b5 100644
--- a/core/src/main/scala/cats/FlatMap.scala
+++ b/core/src/main/scala/cats/FlatMap.scala
@@ -149,4 +149,50 @@ import simulacrum.noop
    */
   def flatTap[A, B](fa: F[A])(f: A => F[B]): F[A] =
     flatMap(fa)(a => as(f(a), a))
+
+  /**
+   * Like an infinite loop of >> calls. This is most useful effect loops
+   * that you want to run forever in for instance a server.
+   *
+   * This will be an infinite loop, or it will return an F[Nothing].
+   *
+   * Be careful using this.
+   * For instance, a List of length k will produce a list of length k^n at iteration
+   * n. This means if k = 0, we return an empty list, if k = 1, we loop forever
+   * allocating single element lists, but if we have a k > 1, we will allocate
+   * exponentially increasing memory and very quickly OOM.
+   */
+  @noop
+  def foreverM[A, B](fa: F[A]): F[B] = {
+    // allocate two things once for efficiency.
+    val leftUnit = Left(())
+    val stepResult: F[Either[Unit, B]] = map(fa)(_ => leftUnit)
+    tailRecM(())(_ => stepResult)
+  }
+
+  /**
+   * iterateForeverM is almost exclusively useful for effect types. For instance,
+   * A may be some state, we may take the current state, run some effect to get
+   * a new state and repeat.
+   */
+  @noop
+  def iterateForeverM[A, B](a: A)(f: A => F[A]): F[B] =
+    tailRecM[A, B](a)(f.andThen { fa =>
+      map(fa)(Left(_): Either[A, B])
+    })
+
+  /**
+   * This repeats an F until we get defined values. This can be useful
+   * for polling type operations on State (or RNG) Monads, or in effect
+   * monads.
+   */
+  @noop
+  def untilDefinedM[A](foa: F[Option[A]]): F[A] = {
+    val leftUnit: Either[Unit, A] = Left(())
+    val feither: F[Either[Unit, A]] = map(foa) {
+      case None    => leftUnit
+      case Some(a) => Right(a)
+    }
+    tailRecM(())(_ => feither)
+  }
 }
diff --git a/core/src/main/scala/cats/syntax/flatMap.scala b/core/src/main/scala/cats/syntax/flatMap.scala
index 7cf0e24daf..17f8e15e77 100644
--- a/core/src/main/scala/cats/syntax/flatMap.scala
+++ b/core/src/main/scala/cats/syntax/flatMap.scala
@@ -54,13 +54,7 @@ final class FlatMapOps[F[_], A](private val fa: F[A]) extends AnyVal {
    * allocating single element lists, but if we have a k > 1, we will allocate
    * exponentially increasing memory and very quickly OOM.
    */
-  def foreverM[B](implicit F: FlatMap[F]): F[B] = {
-    // allocate two things once for efficiency.
-    val leftUnit = Left(())
-    val stepResult: F[Either[Unit, B]] = F.map(fa)(_ => leftUnit)
-    F.tailRecM(())(_ => stepResult)
-  }
-
+  def foreverM[B](implicit F: FlatMap[F]): F[B] = F.foreverM[A, B](fa)
 }
 
 final class FlattenOps[F[_], A](private val ffa: F[F[A]]) extends AnyVal {
@@ -124,10 +118,7 @@ final class FlatMapIdOps[A](private val a: A) extends AnyVal {
    * A may be some state, we may take the current state, run some effect to get
    * a new state and repeat.
    */
-  def iterateForeverM[F[_], B](f: A => F[A])(implicit F: FlatMap[F]): F[B] =
-    tailRecM[F, B](f.andThen { fa =>
-      F.map(fa)(Left(_): Either[A, B])
-    })
+  def iterateForeverM[F[_], B](f: A => F[A])(implicit F: FlatMap[F]): F[B] = F.iterateForeverM[A, B](a)(f)
 }
 
 trait FlatMapOptionSyntax {
@@ -142,12 +133,5 @@ final class FlatMapOptionOps[F[_], A](private val fopta: F[Option[A]]) extends A
    * for polling type operations on State (or RNG) Monads, or in effect
    * monads.
    */
-  def untilDefinedM(implicit F: FlatMap[F]): F[A] = {
-    val leftUnit: Either[Unit, A] = Left(())
-    val feither: F[Either[Unit, A]] = F.map(fopta) {
-      case None    => leftUnit
-      case Some(a) => Right(a)
-    }
-    F.tailRecM(())(_ => feither)
-  }
+  def untilDefinedM(implicit F: FlatMap[F]): F[A] = F.untilDefinedM[A](fopta)
 }

From 63b2d8bd2888efa0bbfb1bbf0844088d4f31f338 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 08:01:03 -0600
Subject: [PATCH 08/16] Add findM to Foldable

---
 core/src/main/scala/cats/Foldable.scala       | 32 ++++++++++++++++++-
 .../src/main/scala/cats/syntax/foldable.scala |  6 +---
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/core/src/main/scala/cats/Foldable.scala b/core/src/main/scala/cats/Foldable.scala
index 5b672a7d3d..aa797dbe5f 100644
--- a/core/src/main/scala/cats/Foldable.scala
+++ b/core/src/main/scala/cats/Foldable.scala
@@ -3,7 +3,7 @@ package cats
 import scala.collection.mutable
 import cats.instances.either._
 import cats.kernel.CommutativeMonoid
-import simulacrum.typeclass
+import simulacrum.{noop, typeclass}
 import Foldable.sentinel
 
 /**
@@ -423,6 +423,36 @@ import Foldable.sentinel
       if (f(a)) Now(Some(a)) else lb
     }.value
 
+  /**
+   * Find the first element matching the effectful predicate, if one exists.
+   *
+   * If there are no elements, the result is `None`. `findM` short-circuits,
+   * i.e. once an element is found, no further effects are produced.
+   *
+   * For example:
+   * {{{
+   * scala> import cats.implicits._
+   * scala> val list = List(1,2,3,4)
+   * scala> Foldable[List].findM(list)(n => (n >= 2).asRight[String])
+   * res0: Either[String,Option[Int]] = Right(Some(2))
+   *
+   * scala> Foldable[List].findM(list)(n => (n > 4).asRight[String])
+   * res1: Either[String,Option[Int]] = Right(None)
+   *
+   * scala> Foldable[List].findM(list)(n => Either.cond(n < 3, n >= 2, "error"))
+   * res2: Either[String,Option[Int]] = Right(Some(2))
+   *
+   * scala> Foldable[List].findM(list)(n => Either.cond(n < 3, false, "error"))
+   * res3: Either[String,Option[Int]] = Left(error)
+   * }}}
+   */
+  @noop
+  def findM[G[_], A](fa: F[A])(p: A => G[Boolean])(implicit G: Monad[G]): G[Option[A]] =
+    G.tailRecM(Foldable.Source.fromFoldable(fa)(self))(_.uncons match {
+      case Some((a, src)) => G.map(p(a))(if (_) Right(Some(a)) else Left(src.value))
+      case None           => G.pure(Right(None))
+    })
+
   /**
    * Check whether at least one element satisfies the predicate.
    *
diff --git a/core/src/main/scala/cats/syntax/foldable.scala b/core/src/main/scala/cats/syntax/foldable.scala
index 53157f0c99..b2cde5a8a7 100644
--- a/core/src/main/scala/cats/syntax/foldable.scala
+++ b/core/src/main/scala/cats/syntax/foldable.scala
@@ -166,11 +166,7 @@ final class FoldableOps[F[_], A](private val fa: F[A]) extends AnyVal {
    * res3: Either[String,Option[Int]] = Left(error)
    * }}}
    */
-  def findM[G[_]](p: A => G[Boolean])(implicit F: Foldable[F], G: Monad[G]): G[Option[A]] =
-    G.tailRecM(Foldable.Source.fromFoldable(fa))(_.uncons match {
-      case Some((a, src)) => G.map(p(a))(if (_) Right(Some(a)) else Left(src.value))
-      case None           => G.pure(Right(None))
-    })
+  def findM[G[_]](p: A => G[Boolean])(implicit F: Foldable[F], G: Monad[G]): G[Option[A]] = F.findM[G, A](fa)(p)
 
   /**
    * Tear down a subset of this structure using a `PartialFunction`.

From 0ea41834c68b24a41f5fc61f3e467c09fab12d35 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 08:07:19 -0600
Subject: [PATCH 09/16] Add reduceMapK to Reducible

---
 core/src/main/scala/cats/Reducible.scala       | 18 +++++++++++++++++-
 .../src/main/scala/cats/syntax/reducible.scala |  3 +--
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/core/src/main/scala/cats/Reducible.scala b/core/src/main/scala/cats/Reducible.scala
index f41161b558..6bb748a413 100644
--- a/core/src/main/scala/cats/Reducible.scala
+++ b/core/src/main/scala/cats/Reducible.scala
@@ -1,7 +1,7 @@
 package cats
 
 import cats.data.{Ior, NonEmptyList}
-import simulacrum.typeclass
+import simulacrum.{noop, typeclass}
 
 /**
  * Data structures that can be reduced to a summary value.
@@ -54,6 +54,22 @@ import simulacrum.typeclass
   def reduceMap[A, B](fa: F[A])(f: A => B)(implicit B: Semigroup[B]): B =
     reduceLeftTo(fa)(f)((b, a) => B.combine(b, f(a)))
 
+  /**
+   * Apply `f` to each element of `fa` and combine them using the
+   * given `SemigroupK[G]`.
+   *
+   * {{{
+   * scala> import cats._, cats.data._, cats.implicits._
+   * scala> val f: Int => Endo[String] = i => (s => s + i)
+   * scala> val x: Endo[String] = Reducible[NonEmptyList].reduceMapK(NonEmptyList.of(1, 2, 3))(f)
+   * scala> val a = x("foo")
+   * a: String = "foo321"
+   * }}}
+   * */
+  @noop
+  def reduceMapK[G[_], A, B](fa: F[A])(f: A => G[B])(implicit G: SemigroupK[G]): G[B] =
+    reduceLeftTo(fa)(f)((b, a) => G.combineK(b, f(a)))
+
   /**
    * Apply `f` to the "initial element" of `fa` and combine it with
    * every other value using the given function `g`.
diff --git a/core/src/main/scala/cats/syntax/reducible.scala b/core/src/main/scala/cats/syntax/reducible.scala
index 3e5904ef52..76e1ff1faf 100644
--- a/core/src/main/scala/cats/syntax/reducible.scala
+++ b/core/src/main/scala/cats/syntax/reducible.scala
@@ -29,6 +29,5 @@ final class ReducibleOps0[F[_], A](private val fa: F[A]) extends AnyVal {
    * a: String = "foo321"
    * }}}
    * */
-  def reduceMapK[G[_], B](f: A => G[B])(implicit F: Reducible[F], G: SemigroupK[G]): G[B] =
-    F.reduceLeftTo(fa)(f)((b, a) => G.combineK(b, f(a)))
+  def reduceMapK[G[_], B](f: A => G[B])(implicit F: Reducible[F], G: SemigroupK[G]): G[B] = F.reduceMapK[G, A, B](fa)(f)
 }

From 762cb2c0771a7ae8f73babc088cb3e48f6db216a Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 08:12:29 -0600
Subject: [PATCH 10/16] Add collectFirstSomeM to Foldable

---
 core/src/main/scala/cats/Foldable.scala       | 39 +++++++++++++++++++
 .../src/main/scala/cats/syntax/foldable.scala |  9 +----
 2 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/core/src/main/scala/cats/Foldable.scala b/core/src/main/scala/cats/Foldable.scala
index aa797dbe5f..13878c882a 100644
--- a/core/src/main/scala/cats/Foldable.scala
+++ b/core/src/main/scala/cats/Foldable.scala
@@ -269,6 +269,45 @@ import Foldable.sentinel
       if (ob.isDefined) Eval.now(ob) else lb
     }.value
 
+  /**
+   * Monadic version of `collectFirstSome`.
+   *
+   * If there are no elements, the result is `None`. `collectFirstSomeM` short-circuits,
+   * i.e. once a Some element is found, no further effects are produced.
+   *
+   * For example:
+   * {{{
+   * scala> import cats.implicits._
+   * scala> def parseInt(s: String): Either[String, Int] = Either.catchOnly[NumberFormatException](s.toInt).leftMap(_.getMessage)
+   * scala> val keys1 = List("1", "2", "4", "5")
+   * scala> val map1 = Map(4 -> "Four", 5 -> "Five")
+   * scala> Foldable[List].collectFirstSomeM(keys1)(parseInt(_) map map1.get)
+   * res0: scala.util.Either[String,Option[String]] = Right(Some(Four))
+   *
+   * scala> val map2 = Map(6 -> "Six", 7 -> "Seven")
+   * scala> Foldable[List].collectFirstSomeM(keys1)(parseInt(_) map map2.get)
+   * res1: scala.util.Either[String,Option[String]] = Right(None)
+   *
+   * scala> val keys2 = List("1", "x", "4", "5")
+   * scala> Foldable[List].collectFirstSomeM(keys2)(parseInt(_) map map1.get)
+   * res2: scala.util.Either[String,Option[String]] = Left(For input string: "x")
+   *
+   * scala> val keys3 = List("1", "2", "4", "x")
+   * scala> Foldable[List].collectFirstSomeM(keys3)(parseInt(_) map map1.get)
+   * res3: scala.util.Either[String,Option[String]] = Right(Some(Four))
+   * }}}
+   */
+  @noop
+  def collectFirstSomeM[G[_], A, B](fa: F[A])(f: A => G[Option[B]])(implicit G: Monad[G]): G[Option[B]] =
+    G.tailRecM(Foldable.Source.fromFoldable(fa)(self))(_.uncons match {
+      case Some((a, src)) =>
+        G.map(f(a)) {
+          case None => Left(src.value)
+          case s    => Right(s)
+        }
+      case None => G.pure(Right(None))
+    })
+
   /**
    * Fold implemented using the given Monoid[A] instance.
    */
diff --git a/core/src/main/scala/cats/syntax/foldable.scala b/core/src/main/scala/cats/syntax/foldable.scala
index b2cde5a8a7..fe1a2866ee 100644
--- a/core/src/main/scala/cats/syntax/foldable.scala
+++ b/core/src/main/scala/cats/syntax/foldable.scala
@@ -134,14 +134,7 @@ final class FoldableOps[F[_], A](private val fa: F[A]) extends AnyVal {
    * }}}
    */
   def collectFirstSomeM[G[_], B](f: A => G[Option[B]])(implicit F: Foldable[F], G: Monad[G]): G[Option[B]] =
-    G.tailRecM(Foldable.Source.fromFoldable(fa))(_.uncons match {
-      case Some((a, src)) =>
-        G.map(f(a)) {
-          case None => Left(src.value)
-          case s    => Right(s)
-        }
-      case None => G.pure(Right(None))
-    })
+    F.collectFirstSomeM[G, A, B](fa)(f)
 
   /**
    * Find the first element matching the effectful predicate, if one exists.

From 30d556e4654e45fc781ccf389d75953a5b9d8e23 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 08:20:00 -0600
Subject: [PATCH 11/16] Add collectFold and collectFoldSome to Foldable

---
 core/src/main/scala/cats/Foldable.scala       | 32 +++++++++++++++++++
 .../src/main/scala/cats/syntax/foldable.scala | 13 ++------
 2 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/core/src/main/scala/cats/Foldable.scala b/core/src/main/scala/cats/Foldable.scala
index 13878c882a..3a24d9134e 100644
--- a/core/src/main/scala/cats/Foldable.scala
+++ b/core/src/main/scala/cats/Foldable.scala
@@ -308,6 +308,38 @@ import Foldable.sentinel
       case None => G.pure(Right(None))
     })
 
+  /**
+   * Tear down a subset of this structure using a `PartialFunction`.
+   *{{{
+   * scala> import cats.implicits._
+   * scala> val xs = List(1, 2, 3, 4)
+   * scala> Foldable[List].collectFold(xs) { case n if n % 2 == 0 => n }
+   * res0: Int = 6
+   *}}}
+   */
+  @noop
+  def collectFold[A, B](fa: F[A])(f: PartialFunction[A, B])(implicit B: Monoid[B]): B =
+    foldLeft(fa, B.empty)((acc, a) => B.combine(acc, f.applyOrElse(a, (_: A) => B.empty)))
+
+  /**
+   * Tear down a subset of this structure using a `A => Option[M]`.
+   *{{{
+   * scala> import cats.implicits._
+   * scala> val xs = List(1, 2, 3, 4)
+   * scala> def f(n: Int): Option[Int] = if (n % 2 == 0) Some(n) else None
+   * scala> Foldable[List].collectSomeFold(xs)(f)
+   * res0: Int = 6
+   *}}}
+   */
+  def collectFoldSome[A, B](fa: F[A])(f: A => Option[B])(implicit B: Monoid[B]): B =
+    foldLeft(fa, B.empty)(
+      (acc, a) =>
+        f(a) match {
+          case Some(x) => B.combine(acc, x)
+          case None    => acc
+        }
+    )
+
   /**
    * Fold implemented using the given Monoid[A] instance.
    */
diff --git a/core/src/main/scala/cats/syntax/foldable.scala b/core/src/main/scala/cats/syntax/foldable.scala
index fe1a2866ee..843f12be35 100644
--- a/core/src/main/scala/cats/syntax/foldable.scala
+++ b/core/src/main/scala/cats/syntax/foldable.scala
@@ -170,8 +170,7 @@ final class FoldableOps[F[_], A](private val fa: F[A]) extends AnyVal {
    * res0: Int = 6
    *}}}
    */
-  def collectFold[M](f: PartialFunction[A, M])(implicit F: Foldable[F], M: Monoid[M]): M =
-    F.foldLeft(fa, M.empty)((acc, a) => M.combine(acc, f.applyOrElse(a, (_: A) => M.empty)))
+  def collectFold[M](f: PartialFunction[A, M])(implicit F: Foldable[F], M: Monoid[M]): M = F.collectFold[A, M](fa)(f)
 
   /**
    * Tear down a subset of this structure using a `A => Option[M]`.
@@ -183,14 +182,8 @@ final class FoldableOps[F[_], A](private val fa: F[A]) extends AnyVal {
    * res0: Int = 6
    *}}}
    */
-  def collectSomeFold[M](f: A => Option[M])(implicit F: Foldable[F], M: Monoid[M]): M =
-    F.foldLeft(fa, M.empty)(
-      (acc, a) =>
-        f(a) match {
-          case Some(x) => M.combine(acc, x)
-          case None    => acc
-        }
-    )
+  @deprecated("Use collectFoldSome", "2.1.0-RC1")
+  def collectSomeFold[M](f: A => Option[M])(implicit F: Foldable[F], M: Monoid[M]): M = F.collectFoldSome[A, M](fa)(f)
 }
 
 final class FoldableOps0[F[_], A](private val fa: F[A]) extends AnyVal {

From 20deedb3d040a387fa8271bc609cb81ebb656ded Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 08:27:26 -0600
Subject: [PATCH 12/16] Fix doc test

---
 core/src/main/scala/cats/Foldable.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/src/main/scala/cats/Foldable.scala b/core/src/main/scala/cats/Foldable.scala
index 3a24d9134e..a895fb5686 100644
--- a/core/src/main/scala/cats/Foldable.scala
+++ b/core/src/main/scala/cats/Foldable.scala
@@ -327,7 +327,7 @@ import Foldable.sentinel
    * scala> import cats.implicits._
    * scala> val xs = List(1, 2, 3, 4)
    * scala> def f(n: Int): Option[Int] = if (n % 2 == 0) Some(n) else None
-   * scala> Foldable[List].collectSomeFold(xs)(f)
+   * scala> Foldable[List].collectFoldSome(xs)(f)
    * res0: Int = 6
    *}}}
    */

From b689e54ceedcd3ac9ee1661e57815cc04904f063 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 08:34:45 -0600
Subject: [PATCH 13/16] Fix doc test

---
 core/src/main/scala/cats/syntax/foldable.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/src/main/scala/cats/syntax/foldable.scala b/core/src/main/scala/cats/syntax/foldable.scala
index 843f12be35..9af56d091d 100644
--- a/core/src/main/scala/cats/syntax/foldable.scala
+++ b/core/src/main/scala/cats/syntax/foldable.scala
@@ -178,7 +178,7 @@ final class FoldableOps[F[_], A](private val fa: F[A]) extends AnyVal {
    * scala> import cats.implicits._
    * scala> val xs = List(1, 2, 3, 4)
    * scala> def f(n: Int): Option[Int] = if (n % 2 == 0) Some(n) else None
-   * scala> xs.collectSomeFold(f)
+   * scala> xs.collectFoldSome(f)
    * res0: Int = 6
    *}}}
    */

From 5867e6673a0f98c56d962df753577f964641b7d1 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 08:27:02 -0600
Subject: [PATCH 14/16] Move Foldable extension methods onto Foldable

---
 core/src/main/scala/cats/Foldable.scala       | 78 +++++++++++++++++++
 .../src/main/scala/cats/syntax/foldable.scala | 52 ++++---------
 2 files changed, 93 insertions(+), 37 deletions(-)

diff --git a/core/src/main/scala/cats/Foldable.scala b/core/src/main/scala/cats/Foldable.scala
index a895fb5686..aae1941fdb 100644
--- a/core/src/main/scala/cats/Foldable.scala
+++ b/core/src/main/scala/cats/Foldable.scala
@@ -726,6 +726,84 @@ import Foldable.sentinel
 
   override def unorderedFoldMap[A, B: CommutativeMonoid](fa: F[A])(f: (A) => B): B =
     foldMap(fa)(f)
+
+  /**
+   * Separate this Foldable into a Tuple by a separating function `A => H[B, C]` for some `Bifoldable[H]`
+   * Equivalent to `Functor#map` and then `Alternative#separate`.
+   *
+   * {{{
+   * scala> import cats.implicits._, cats.Foldable, cats.data.Const
+   * scala> val list = List(1,2,3,4)
+   * scala> Foldable[List].partitionBifold(list)(a => ("value " + a.toString(), if (a % 2 == 0) -a else a))
+   * res0: (List[String], List[Int]) = (List(value 1, value 2, value 3, value 4),List(1, -2, 3, -4))
+   * scala> Foldable[List].partitionBifold(list)(a => Const[Int, Nothing with Any](a))
+   * res1: (List[Int], List[Nothing with Any]) = (List(1, 2, 3, 4),List())
+   * }}}
+   */
+  @noop
+  def partitionBifold[H[_, _], A, B, C](fa: F[A])(f: A => H[B, C])(implicit A: Alternative[F],
+                                                                   H: Bifoldable[H]): (F[B], F[C]) = {
+    import cats.instances.tuple._
+
+    implicit val mb: Monoid[F[B]] = A.algebra[B]
+    implicit val mc: Monoid[F[C]] = A.algebra[C]
+
+    foldMap[A, (F[B], F[C])](fa)(
+      a => H.bifoldMap[B, C, (F[B], F[C])](f(a))(b => (A.pure(b), A.empty[C]), c => (A.empty[B], A.pure(c)))
+    )
+  }
+
+  /**
+   * Separate this Foldable into a Tuple by an effectful separating function `A => G[H[B, C]]` for some `Bifoldable[H]`
+   * Equivalent to `Traverse#traverse` over `Alternative#separate`
+   *
+   * {{{
+   * scala> import cats.implicits._, cats.Foldable, cats.data.Const
+   * scala> val list = List(1,2,3,4)
+   * `Const`'s second parameter is never instantiated, so we can use an impossible type:
+   * scala> Foldable[List].partitionBifoldM(list)(a => Option(Const[Int, Nothing with Any](a)))
+   * res0: Option[(List[Int], List[Nothing with Any])] = Some((List(1, 2, 3, 4),List()))
+   * }}}
+   */
+  @noop
+  def partitionBifoldM[G[_], H[_, _], A, B, C](
+    fa: F[A]
+  )(f: A => G[H[B, C]])(implicit A: Alternative[F], M: Monad[G], H: Bifoldable[H]): G[(F[B], F[C])] = {
+    import cats.instances.tuple._
+
+    implicit val mb: Monoid[F[B]] = A.algebra[B]
+    implicit val mc: Monoid[F[C]] = A.algebra[C]
+
+    foldMapM[G, A, (F[B], F[C])](fa)(
+      a =>
+        M.map(f(a)) {
+          H.bifoldMap[B, C, (F[B], F[C])](_)(b => (A.pure(b), A.empty[C]), c => (A.empty[B], A.pure(c)))
+        }
+    )
+  }
+
+  /**
+   * Separate this Foldable into a Tuple by an effectful separating function `A => G[Either[B, C]]`
+   * Equivalent to `Traverse#traverse` over `Alternative#separate`
+   *
+   * {{{
+   * scala> import cats.implicits._, cats.Foldable, cats.Eval
+   * scala> val list = List(1,2,3,4)
+   * scala> val partitioned1 = Foldable[List].partitionEitherM(list)(a => if (a % 2 == 0) Eval.now(Either.left[String, Int](a.toString)) else Eval.now(Either.right[String, Int](a)))
+   * Since `Eval.now` yields a lazy computation, we need to force it to inspect the result:
+   * scala> partitioned1.value
+   * res0: (List[String], List[Int]) = (List(2, 4),List(1, 3))
+   * scala> val partitioned2 = Foldable[List].partitionEitherM(list)(a => Eval.later(Either.right(a * 4)))
+   * scala> partitioned2.value
+   * res1: (List[Nothing], List[Int]) = (List(),List(4, 8, 12, 16))
+   * }}}
+   */
+  @noop
+  def partitionEitherM[G[_], A, B, C](fa: F[A])(f: A => G[Either[B, C]])(implicit A: Alternative[F],
+                                                                         M: Monad[G]): G[(F[B], F[C])] = {
+    import cats.instances.either._
+    partitionBifoldM[G, Either, A, B, C](fa)(f)(A, M, Bifoldable[Either])
+  }
 }
 
 object Foldable {
diff --git a/core/src/main/scala/cats/syntax/foldable.scala b/core/src/main/scala/cats/syntax/foldable.scala
index 9af56d091d..c4af904bcb 100644
--- a/core/src/main/scala/cats/syntax/foldable.scala
+++ b/core/src/main/scala/cats/syntax/foldable.scala
@@ -15,7 +15,8 @@ private[syntax] trait FoldableSyntaxBinCompat0 {
 }
 
 private[syntax] trait FoldableSyntaxBinCompat1 {
-  implicit final def catsSyntaxFoldableBinCompat0[F[_]](fa: Foldable[F]): FoldableOps1[F] =
+  @deprecated("Use methods on Foldable", "2.1.0-RC1")
+  final def catsSyntaxFoldableBinCompat0[F[_]](fa: Foldable[F]): FoldableOps1[F] =
     new FoldableOps1(fa)
 }
 
@@ -239,10 +240,8 @@ final class FoldableOps0[F[_], A](private val fa: F[A]) extends AnyVal {
    */
   def partitionBifold[H[_, _], B, C](
     f: A => H[B, C]
-  )(implicit A: Alternative[F], F: Foldable[F], H: Bifoldable[H]): (F[B], F[C]) = {
-    import cats.syntax.foldable._
+  )(implicit A: Alternative[F], F: Foldable[F], H: Bifoldable[H]): (F[B], F[C]) =
     F.partitionBifold[H, A, B, C](fa)(f)(A, H)
-  }
 
   /**
    * Separate this Foldable into a Tuple by an effectful separating function `A => G[H[B, C]]` for some `Bifoldable[H]`
@@ -258,10 +257,8 @@ final class FoldableOps0[F[_], A](private val fa: F[A]) extends AnyVal {
    */
   def partitionBifoldM[G[_], H[_, _], B, C](
     f: A => G[H[B, C]]
-  )(implicit A: Alternative[F], F: Foldable[F], M: Monad[G], H: Bifoldable[H]): G[(F[B], F[C])] = {
-    import cats.syntax.foldable._
+  )(implicit A: Alternative[F], F: Foldable[F], M: Monad[G], H: Bifoldable[H]): G[(F[B], F[C])] =
     F.partitionBifoldM[G, H, A, B, C](fa)(f)(A, M, H)
-  }
 
   /**
    * Separate this Foldable into a Tuple by an effectful separating function `A => G[Either[B, C]]`
@@ -281,12 +278,11 @@ final class FoldableOps0[F[_], A](private val fa: F[A]) extends AnyVal {
    */
   def partitionEitherM[G[_], B, C](
     f: A => G[Either[B, C]]
-  )(implicit A: Alternative[F], F: Foldable[F], M: Monad[G]): G[(F[B], F[C])] = {
-    import cats.syntax.foldable._
+  )(implicit A: Alternative[F], F: Foldable[F], M: Monad[G]): G[(F[B], F[C])] =
     F.partitionEitherM[G, A, B, C](fa)(f)(A, M)
-  }
 }
 
+@deprecated("Use methods on Foldable", "2.1.0-RC1")
 final private[syntax] class FoldableOps1[F[_]](private val F: Foldable[F]) extends AnyVal {
 
   /**
@@ -302,17 +298,10 @@ final private[syntax] class FoldableOps1[F[_]](private val F: Foldable[F]) exten
    * res1: (List[Int], List[Nothing with Any]) = (List(1, 2, 3, 4),List())
    * }}}
    */
+  @deprecated("Use partitionBifold on Foldable", "2.1.0-RC1")
   def partitionBifold[H[_, _], A, B, C](fa: F[A])(f: A => H[B, C])(implicit A: Alternative[F],
-                                                                   H: Bifoldable[H]): (F[B], F[C]) = {
-    import cats.instances.tuple._
-
-    implicit val mb: Monoid[F[B]] = A.algebra[B]
-    implicit val mc: Monoid[F[C]] = A.algebra[C]
-
-    F.foldMap[A, (F[B], F[C])](fa)(
-      a => H.bifoldMap[B, C, (F[B], F[C])](f(a))(b => (A.pure(b), A.empty[C]), c => (A.empty[B], A.pure(c)))
-    )
-  }
+                                                                   H: Bifoldable[H]): (F[B], F[C]) =
+    F.partitionBifold[H, A, B, C](fa)(f)
 
   /**
    * Separate this Foldable into a Tuple by an effectful separating function `A => G[H[B, C]]` for some `Bifoldable[H]`
@@ -326,21 +315,11 @@ final private[syntax] class FoldableOps1[F[_]](private val F: Foldable[F]) exten
    * res0: Option[(List[Int], List[Nothing with Any])] = Some((List(1, 2, 3, 4),List()))
    * }}}
    */
+  @deprecated("Use partitionBifoldM on Foldable", "2.1.0-RC1")
   def partitionBifoldM[G[_], H[_, _], A, B, C](
     fa: F[A]
-  )(f: A => G[H[B, C]])(implicit A: Alternative[F], M: Monad[G], H: Bifoldable[H]): G[(F[B], F[C])] = {
-    import cats.instances.tuple._
-
-    implicit val mb: Monoid[F[B]] = A.algebra[B]
-    implicit val mc: Monoid[F[C]] = A.algebra[C]
-
-    F.foldMapM[G, A, (F[B], F[C])](fa)(
-      a =>
-        M.map(f(a)) {
-          H.bifoldMap[B, C, (F[B], F[C])](_)(b => (A.pure(b), A.empty[C]), c => (A.empty[B], A.pure(c)))
-        }
-    )
-  }
+  )(f: A => G[H[B, C]])(implicit A: Alternative[F], M: Monad[G], H: Bifoldable[H]): G[(F[B], F[C])] =
+    F.partitionBifoldM[G, H, A, B, C](fa)(f)
 
   /**
    * Separate this Foldable into a Tuple by an effectful separating function `A => G[Either[B, C]]`
@@ -358,9 +337,8 @@ final private[syntax] class FoldableOps1[F[_]](private val F: Foldable[F]) exten
    * res1: (List[Nothing], List[Int]) = (List(),List(4, 8, 12, 16))
    * }}}
    */
+  @deprecated("Use partitionEitherM on Foldable", "2.1.0-RC1")
   def partitionEitherM[G[_], A, B, C](fa: F[A])(f: A => G[Either[B, C]])(implicit A: Alternative[F],
-                                                                         M: Monad[G]): G[(F[B], F[C])] = {
-    import cats.instances.either._
-    partitionBifoldM[G, Either, A, B, C](fa)(f)(A, M, Bifoldable[Either])
-  }
+                                                                         M: Monad[G]): G[(F[B], F[C])] =
+    F.partitionEitherM[G, A, B, C](fa)(f)
 }

From 4402e0dfc964c90e891b26613bb1b90fcf6b6664 Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 08:34:18 -0600
Subject: [PATCH 15/16] Add foldMapK to Foldable

---
 core/src/main/scala/cats/Foldable.scala        | 16 ++++++++++++++++
 core/src/main/scala/cats/syntax/foldable.scala |  3 +--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/core/src/main/scala/cats/Foldable.scala b/core/src/main/scala/cats/Foldable.scala
index aae1941fdb..681fa84d55 100644
--- a/core/src/main/scala/cats/Foldable.scala
+++ b/core/src/main/scala/cats/Foldable.scala
@@ -384,6 +384,22 @@ import Foldable.sentinel
     }
   }
 
+  /**
+   * Fold implemented by mapping `A` values into `B` in a context `G` and then
+   * combining them using the `MonoidK[G]` instance.
+   *
+   * {{{
+   * scala> import cats._, cats.implicits._
+   * scala> val f: Int => Endo[String] = i => (s => s + i)
+   * scala> val x: Endo[String] = Foldable[List].foldMapK(List(1, 2, 3))(f)
+   * scala> val a = x("foo")
+   * a: String = "foo321"
+   * }}}
+   * */
+  @noop
+  def foldMapK[G[_], A, B](fa: F[A])(f: A => G[B])(implicit G: MonoidK[G]): G[B] =
+    foldMap(fa)(f)(G.algebra)
+
   /**
    * Alias for [[foldM]].
    */
diff --git a/core/src/main/scala/cats/syntax/foldable.scala b/core/src/main/scala/cats/syntax/foldable.scala
index c4af904bcb..ebba15ea7f 100644
--- a/core/src/main/scala/cats/syntax/foldable.scala
+++ b/core/src/main/scala/cats/syntax/foldable.scala
@@ -221,8 +221,7 @@ final class FoldableOps0[F[_], A](private val fa: F[A]) extends AnyVal {
    * a: String = "foo321"
    * }}}
    * */
-  def foldMapK[G[_], B](f: A => G[B])(implicit F: Foldable[F], G: MonoidK[G]): G[B] =
-    F.foldMap(fa)(f)(G.algebra)
+  def foldMapK[G[_], B](f: A => G[B])(implicit F: Foldable[F], G: MonoidK[G]): G[B] = F.foldMapK(fa)(f)
 
   /**
    * Separate this Foldable into a Tuple by an effectful separating function `A => H[B, C]` for some `Bifoldable[H]`

From 7b30d5b2463f9e85d0db6054cf9d9f290b2a774c Mon Sep 17 00:00:00 2001
From: Travis Brown <travisrobertbrown@gmail.com>
Date: Thu, 14 Nov 2019 08:50:03 -0600
Subject: [PATCH 16/16] Clean up redundant syntax methods

---
 .../scala/cats/syntax/applicativeError.scala  | 34 ++-------------
 .../src/main/scala/cats/syntax/foldable.scala | 41 -------------------
 2 files changed, 3 insertions(+), 72 deletions(-)

diff --git a/core/src/main/scala/cats/syntax/applicativeError.scala b/core/src/main/scala/cats/syntax/applicativeError.scala
index 1e399062aa..10125e46fe 100644
--- a/core/src/main/scala/cats/syntax/applicativeError.scala
+++ b/core/src/main/scala/cats/syntax/applicativeError.scala
@@ -26,41 +26,13 @@ private[syntax] trait ApplicativeErrorExtension {
     new ApplicativeErrorExtensionOps(F)
 }
 
+@deprecated("Use methods on ApplicativeError", "2.1.0-RC1")
 final private[syntax] class ApplicativeErrorExtensionOps[F[_], E](F: ApplicativeError[F, E]) {
 
-  /**
-   * Convert from scala.Option
-   *
-   * Example:
-   * {{{
-   * scala> import cats.implicits._
-   * scala> import cats.ApplicativeError
-   * scala> val F = ApplicativeError[Either[String, *], String]
-   *
-   * scala> F.fromOption(Some(1), "Empty")
-   * res0: scala.Either[String, Int] = Right(1)
-   *
-   * scala> F.fromOption(Option.empty[Int], "Empty")
-   * res1: scala.Either[String, Int] = Left(Empty)
-   * }}}
-   */
+  @deprecated("Use fromOption on ApplicativeError", "2.1.0-RC1")
   private[syntax] def fromOption[A](oa: Option[A], ifEmpty: => E): F[A] = F.fromOption(oa, ifEmpty)
 
-  /**
-   * Convert from cats.data.Validated
-   *
-   * Example:
-   * {{{
-   * scala> import cats.implicits._
-   * scala> import cats.ApplicativeError
-   *
-   * scala> ApplicativeError[Option, Unit].fromValidated(1.valid[Unit])
-   * res0: scala.Option[Int] = Some(1)
-   *
-   * scala> ApplicativeError[Option, Unit].fromValidated(().invalid[Int])
-   * res1: scala.Option[Int] = None
-   * }}}
-   */
+  @deprecated("Use fromValidated on ApplicativeError", "2.1.0-RC1")
   private[syntax] def fromValidated[A](x: Validated[E, A]): F[A] = F.fromValidated(x)
 }
 
diff --git a/core/src/main/scala/cats/syntax/foldable.scala b/core/src/main/scala/cats/syntax/foldable.scala
index ebba15ea7f..a09b08754a 100644
--- a/core/src/main/scala/cats/syntax/foldable.scala
+++ b/core/src/main/scala/cats/syntax/foldable.scala
@@ -284,58 +284,17 @@ final class FoldableOps0[F[_], A](private val fa: F[A]) extends AnyVal {
 @deprecated("Use methods on Foldable", "2.1.0-RC1")
 final private[syntax] class FoldableOps1[F[_]](private val F: Foldable[F]) extends AnyVal {
 
-  /**
-   * Separate this Foldable into a Tuple by a separating function `A => H[B, C]` for some `Bifoldable[H]`
-   * Equivalent to `Functor#map` and then `Alternative#separate`.
-   *
-   * {{{
-   * scala> import cats.implicits._, cats.Foldable, cats.data.Const
-   * scala> val list = List(1,2,3,4)
-   * scala> Foldable[List].partitionBifold(list)(a => ("value " + a.toString(), if (a % 2 == 0) -a else a))
-   * res0: (List[String], List[Int]) = (List(value 1, value 2, value 3, value 4),List(1, -2, 3, -4))
-   * scala> Foldable[List].partitionBifold(list)(a => Const[Int, Nothing with Any](a))
-   * res1: (List[Int], List[Nothing with Any]) = (List(1, 2, 3, 4),List())
-   * }}}
-   */
   @deprecated("Use partitionBifold on Foldable", "2.1.0-RC1")
   def partitionBifold[H[_, _], A, B, C](fa: F[A])(f: A => H[B, C])(implicit A: Alternative[F],
                                                                    H: Bifoldable[H]): (F[B], F[C]) =
     F.partitionBifold[H, A, B, C](fa)(f)
 
-  /**
-   * Separate this Foldable into a Tuple by an effectful separating function `A => G[H[B, C]]` for some `Bifoldable[H]`
-   * Equivalent to `Traverse#traverse` over `Alternative#separate`
-   *
-   * {{{
-   * scala> import cats.implicits._, cats.Foldable, cats.data.Const
-   * scala> val list = List(1,2,3,4)
-   * `Const`'s second parameter is never instantiated, so we can use an impossible type:
-   * scala> Foldable[List].partitionBifoldM(list)(a => Option(Const[Int, Nothing with Any](a)))
-   * res0: Option[(List[Int], List[Nothing with Any])] = Some((List(1, 2, 3, 4),List()))
-   * }}}
-   */
   @deprecated("Use partitionBifoldM on Foldable", "2.1.0-RC1")
   def partitionBifoldM[G[_], H[_, _], A, B, C](
     fa: F[A]
   )(f: A => G[H[B, C]])(implicit A: Alternative[F], M: Monad[G], H: Bifoldable[H]): G[(F[B], F[C])] =
     F.partitionBifoldM[G, H, A, B, C](fa)(f)
 
-  /**
-   * Separate this Foldable into a Tuple by an effectful separating function `A => G[Either[B, C]]`
-   * Equivalent to `Traverse#traverse` over `Alternative#separate`
-   *
-   * {{{
-   * scala> import cats.implicits._, cats.Foldable, cats.Eval
-   * scala> val list = List(1,2,3,4)
-   * scala> val partitioned1 = Foldable[List].partitionEitherM(list)(a => if (a % 2 == 0) Eval.now(Either.left[String, Int](a.toString)) else Eval.now(Either.right[String, Int](a)))
-   * Since `Eval.now` yields a lazy computation, we need to force it to inspect the result:
-   * scala> partitioned1.value
-   * res0: (List[String], List[Int]) = (List(2, 4),List(1, 3))
-   * scala> val partitioned2 = Foldable[List].partitionEitherM(list)(a => Eval.later(Either.right(a * 4)))
-   * scala> partitioned2.value
-   * res1: (List[Nothing], List[Int]) = (List(),List(4, 8, 12, 16))
-   * }}}
-   */
   @deprecated("Use partitionEitherM on Foldable", "2.1.0-RC1")
   def partitionEitherM[G[_], A, B, C](fa: F[A])(f: A => G[Either[B, C]])(implicit A: Alternative[F],
                                                                          M: Monad[G]): G[(F[B], F[C])] =