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Deprecate FlatMap's >> and << #1955

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Oct 10, 2017
Merged

Deprecate FlatMap's >> and << #1955

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e44e3d0
Deprecate >> and <<
Oct 7, 2017
b8a302d
Move *> and <* to Apply and make them aliases
Oct 8, 2017
8f35654
Add syntaxTests for *> and <*
Oct 8, 2017
95ac1ab
Move laws
Oct 9, 2017
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16 changes: 16 additions & 0 deletions core/src/main/scala/cats/Apply.scala
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Expand Up @@ -19,6 +19,22 @@ trait Apply[F[_]] extends Functor[F] with Cartesian[F] with ApplyArityFunctions[
override def product[A, B](fa: F[A], fb: F[B]): F[(A, B)] =
ap(map(fa)(a => (b: B) => (a, b)))(fb)

/** Compose two actions, discarding any value produced by the first. */
def followedBy[A, B](fa: F[A])(fb: F[B]): F[B] =
map2(fa, fb)((_, b) => b)

/** Alias for [[followedBy]]. */
@inline final def *>[A, B](fa: F[A])(fb: F[B]): F[B] =
followedBy(fa)(fb)

/** Compose two actions, discarding any value produced by the second. */
def forEffect[A, B](fa: F[A])(fb: F[B]): F[A] =
map2(fa, fb)((a, _) => a)

/** Alias for [[forEffect]]. */
@inline final def <*[A, B](fa: F[A])(fb: F[B]): F[A] =
forEffect(fa)(fb)
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This is untested because <* and << were before this PR.


/**
* ap2 is a binary version of ap, defined in terms of ap.
*/
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8 changes: 0 additions & 8 deletions core/src/main/scala/cats/FlatMap.scala
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Expand Up @@ -44,11 +44,7 @@ import simulacrum.typeclass
def flatten[A](ffa: F[F[A]]): F[A] =
flatMap(ffa)(fa => fa)

/** Sequentially compose two actions, discarding any value produced by the first. */
def followedBy[A, B](fa: F[A])(fb: F[B]): F[B] = flatMap(fa)(_ => fb)

/** Alias for [[followedBy]]. */
@inline final def >>[A, B](fa: F[A])(fb: F[B]): F[B] = followedBy(fa)(fb)

/**
* Sequentially compose two actions, discarding any value produced by the first. This variant of
Expand All @@ -66,11 +62,7 @@ import simulacrum.typeclass
*/
def followedByEval[A, B](fa: F[A])(fb: Eval[F[B]]): F[B] = flatMap(fa)(_ => fb.value)

/** Sequentially compose two actions, discarding any value produced by the second. */
def forEffect[A, B](fa: F[A])(fb: F[B]): F[A] = flatMap(fa)(a => map(fb)(_ => a))

/** Alias for [[forEffect]]. */
@inline final def <<[A, B](fa: F[A])(fb: F[B]): F[A] = forEffect(fa)(fb)

/**
* Sequentially compose two actions, discarding any value produced by the second. This variant of
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6 changes: 0 additions & 6 deletions core/src/main/scala/cats/syntax/cartesian.scala
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Expand Up @@ -17,10 +17,4 @@ abstract class CartesianOps[F[_], A] extends Cartesian.Ops[F, A] {
final def |@|[B](fb: F[B]): CartesianBuilder[F]#CartesianBuilder2[A, B] =
new CartesianBuilder[F] |@| self |@| fb

final def *>[B](fb: F[B])(implicit F: Functor[F]): F[B] =
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Ahh. I see someone put them here originally. This was an error in my view. They should be on Apply.

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Yeah +1 on that :)

F.map(typeClassInstance.product(self, fb)) { case (_, b) => b }

final def <*[B](fb: F[B])(implicit F: Functor[F]): F[A] =
F.map(typeClassInstance.product(self, fb)) { case (a, _) => a }

}
12 changes: 12 additions & 0 deletions core/src/main/scala/cats/syntax/flatMap.scala
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Expand Up @@ -11,6 +11,18 @@ trait FlatMapSyntax extends FlatMap.ToFlatMapOps {

implicit final def catsSyntaxFlatMapIdOps[A](a: A): FlatMapIdOps[A] =
new FlatMapIdOps[A](a)

implicit final def catsSyntaxFlatMapOps[F[_]: FlatMap, A](fa: F[A]): FlatMapOps[F, A] =
new FlatMapOps[F, A](fa)
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These are untested, because of deprecation

}

final class FlatMapOps[F[_], A](val fa: F[A]) extends AnyVal {

@deprecated("Use *> instead", "1.0.0-RC1")
def >>[B](fb: F[B])(implicit F: FlatMap[F]): F[B] = F.followedBy(fa)(fb)

@deprecated("Use <* instead", "1.0.0-RC1")
def <<[B](fb: F[B])(implicit F: FlatMap[F]): F[A] = F.forEffect(fa)(fb)
}

final class FlattenOps[F[_], A](val ffa: F[F[A]]) extends AnyVal {
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8 changes: 4 additions & 4 deletions docs/src/main/tut/faq.md
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Expand Up @@ -210,13 +210,11 @@ All other symbols can be imported with `import cats.implicits._`

| Symbol | Name | Nickname | Type Class | Signature |
| -------------------------------- | ---------------------- | ---------------- | ----------------------- | --------------------------------------------------------- |
| `fa *> fb` | right apply | | `Cartesian[F[_]]` | `*>(fa: F[A])(fb: F[B]): F[B]` |
| `fa <* fb` | left apply | | `Cartesian[F[_]]` | `<*(fa: F[A])(fb: F[B]): F[A]` |
| `fa *> fb` | followed by | | `Apply[F[_]]` | `followedBy(fa: F[A])(fb: F[B]): F[B]` |
| `fa <* fb` | for effect | | `Apply[F[_]]` | `forEffect(fa: F[A])(fb: F[B]): F[A]` |
| `x === y` | equals | | `Eq[A]` | `eqv(x: A, y: A): Boolean` |
| `x =!= y` | not equals | | `Eq[A]` | `neqv(x: A, y: A): Boolean` |
| `fa >>= f` | flatMap | | `FlatMap[F[_]]` | `flatMap(fa: F[A])(f: A => F[B]): F[B]` |
| `fa >> fb` | followed by | | `FlatMap[F[_]]` | `followedBy(fa: F[A])(fb: F[B]): F[B]` |
| `fa << fb` | for effect | | `FlatMap[F[_]]` | `forEffect(fa: F[A])(fb: F[B]): F[A]` |
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Should we not add them back to another place place in the doc?

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I added them at the bottom with a deprecated notice

| <code>x &#124;-&#124; y</code> | remove | | `Group[A]` | `remove(x: A, y: A): A` |
| `x > y` | greater than | | `PartialOrder[A]` | `gt(x: A, y: A): Boolean` |
| `x >= y` | greater than or equal | | `PartialOrder[A]` | `gteq(x: A, y: A): Boolean` |
Expand All @@ -231,6 +229,8 @@ All other symbols can be imported with `import cats.implicits._`
| `F :≺: G` | injectK | | `InjectK[F[_], G[_]]` | `InjectK` alias |
| `⊥` | bottom | | N/A | `Nothing` |
| `⊤` | top | | N/A | `Any` |
| `fa >> fb` (Deprecated) | followed by | | `FlatMap[F[_]]` | `followedBy(fa: F[A])(fb: F[B]): F[B]` |
| `fa << fb` (Deprecated) | for effect | | `FlatMap[F[_]]` | `forEffect(fa: F[A])(fb: F[B]): F[A]` |

## <a id="contributing" href="#contributing"></a>How can I help?

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4 changes: 2 additions & 2 deletions free/src/test/scala/cats/free/FreeTests.scala
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Expand Up @@ -189,8 +189,8 @@ class FreeTests extends CatsSuite {
forAll { (x: Int, y: Int) =>
val expr1: Free[T, Int] = Free.injectRoll[T, Test1Algebra, Int](Test1(x, Free.pure))
val expr2: Free[T, Int] = Free.injectRoll[T, Test2Algebra, Int](Test2(y, Free.pure))
val res = distr[T, Int](expr1 >> expr2)
res == Some(Free.pure(x + y)) should ===(true)
val res = distr[T, Int](expr1 *> expr2)
res.map(_.foldMap(eitherKInterpreter)) should === (Some(Free.pure[Id, Int](x + y).foldMap(FunctionK.id)))
}
}
}
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6 changes: 6 additions & 0 deletions laws/src/main/scala/cats/laws/ApplyLaws.scala
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Expand Up @@ -20,6 +20,12 @@ trait ApplyLaws[F[_]] extends FunctorLaws[F] with CartesianLaws[F] {

def map2EvalConsistency[A, B, C](fa: F[A], fb: F[B], f: (A, B) => C): IsEq[F[C]] =
F.map2(fa, fb)(f) <-> (F.map2Eval(fa, Eval.now(fb))(f).value)

def followedByConsistency[A, B](fa: F[A], fb: F[B]): IsEq[F[B]] =
F.followedBy(fa)(fb) <-> F.map2(fa, fb)((_, b) => b)

def forEffectConsistency[A, B](fa: F[A], fb: F[B]): IsEq[F[A]] =
F.forEffect(fa)(fb) <-> F.map2(fa, fb)((a, _) => a)
}

object ApplyLaws {
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5 changes: 0 additions & 5 deletions laws/src/main/scala/cats/laws/FlatMapLaws.scala
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Expand Up @@ -18,11 +18,6 @@ trait FlatMapLaws[F[_]] extends ApplyLaws[F] {
def flatMapConsistentApply[A, B](fa: F[A], fab: F[A => B]): IsEq[F[B]] =
fab.ap(fa) <-> fab.flatMap(f => fa.map(f))

def followedByConsistency[A, B](fa: F[A], fb: F[B]): IsEq[F[B]] =
F.followedBy(fa)(fb) <-> F.flatMap(fa)(_ => fb)

def forEffectConsistency[A, B](fa: F[A], fb: F[B]): IsEq[F[A]] =
F.forEffect(fa)(fb) <-> F.flatMap(fa)(a => fb.map(_ => a))

/**
* The composition of `cats.data.Kleisli` arrows is associative. This is
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2 changes: 1 addition & 1 deletion tests/src/test/scala/cats/tests/MonadTest.scala
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Expand Up @@ -10,7 +10,7 @@ class MonadTest extends CatsSuite {
val smallPosInt = Gen.choose(1, 5000)

val increment: StateT[Id, Int, Unit] = StateT.modify(_ + 1)
val incrementAndGet: StateT[Id, Int, Int] = increment >> StateT.get
val incrementAndGet: StateT[Id, Int, Int] = increment *> StateT.get

test("whileM_") {
forAll(smallPosInt) { (max: Int) =>
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3 changes: 3 additions & 0 deletions tests/src/test/scala/cats/tests/SyntaxTests.scala
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Expand Up @@ -209,6 +209,9 @@ object SyntaxTests extends AllInstances with AllSyntax {
val f = mock[(A, B, C) => Z]
val ff = mock[F[(A, B, C) => Z]]

fa *> fb
fb <* fc

tfabc mapN f
(fa, fb, fc) mapN f
(fa, fb, fc) apWith ff
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