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Add InvariantSemigroupal and ability to turn Monoidals to Monoids #2088

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merged 24 commits into from
Dec 18, 2017
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Merged

Add InvariantSemigroupal and ability to turn Monoidals to Monoids #2088

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ec1f604
Add InvariantSemigroupal and ability to turn Monoidals to Monoids
Dec 10, 2017
2edcb85
Add Tests
Dec 10, 2017
495cc74
Add composition with Apply
Dec 10, 2017
d8b496d
Add Mima exception
Dec 10, 2017
19dc0ff
More tests + Nested
Dec 12, 2017
38b46e6
Remodel hierarchy
Dec 12, 2017
f4b7490
Move monoid and semigroup functions to the instance
Dec 12, 2017
f9df1c3
More Tests
Dec 12, 2017
5e17eed
Merge branch 'master' into add-monoidal-to-monoid
Dec 12, 2017
8e2f7ab
Use def unit: F[Unit] as base for Monoidal
Dec 13, 2017
3bfaf86
Fix docs and free
Dec 14, 2017
b7f36f2
Fix duplicated mima exclusions
Dec 14, 2017
94b0d2e
Coverage
Dec 14, 2017
5443046
Remove semigroup and monoid from typeclass and rename conquer to trivial
Dec 15, 2017
1a10366
Remove unecceasry instances
Dec 16, 2017
dfbcf66
Merge branch 'master' into add-monoidal-to-monoid
Dec 16, 2017
7880ada
Merge branch 'master' into add-monoidal-to-monoid
Dec 16, 2017
3e3982f
Merge branch 'add-monoidal-to-monoid' of https://github.com/LukaJCB/c…
kailuowang Dec 18, 2017
95f58ff
use uinit for laws
kailuowang Dec 18, 2017
4b73af8
improve test coverage
kailuowang Dec 18, 2017
30391e8
Merge pull request #3 from kailuowang/LukaJCB-add-monoidal-to-monoid
Dec 18, 2017
18f353d
Add more mima exceptions
Dec 18, 2017
436e444
Mima
Dec 18, 2017
ff0a355
Merge branch 'master' into add-monoidal-to-monoid
kailuowang Dec 18, 2017
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95 changes: 95 additions & 0 deletions build.sbt
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Original file line number Diff line number Diff line change
Expand Up @@ -322,6 +322,101 @@ def mimaSettings(moduleName: String) = Seq(
exclude[DirectMissingMethodProblem]("cats.data.RWSTAlternative.sequence"),
exclude[ReversedMissingMethodProblem]("cats.MonadError.rethrow"),
exclude[ReversedMissingMethodProblem]("cats.syntax.MonadErrorSyntax.catsSyntaxMonadErrorRethrow"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.composeApply"),
exclude[DirectMissingMethodProblem]("cats.Semigroupal.catsSemigroupalForMonoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[ReversedMissingMethodProblem]("cats.ContravariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[ReversedMissingMethodProblem]("cats.Applicative.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[ReversedMissingMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[ReversedMissingMethodProblem]("cats.Apply.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantMonoidal.monoid"),
exclude[InheritedNewAbstractMethodProblem]("cats.InvariantSemigroupal.semigroup"),
exclude[ReversedMissingMethodProblem]("cats.instances.InvariantMonoidalInstances.catsSemigroupalForMonoid"),
exclude[DirectMissingMethodProblem]("cats.data.CokleisliArrow.id"),
exclude[IncompatibleResultTypeProblem]("cats.data.CokleisliArrow.id")
)
Expand Down
19 changes: 5 additions & 14 deletions core/src/main/scala/cats/Applicative.scala
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Expand Up @@ -14,20 +14,8 @@ import simulacrum.typeclass
*
* Must obey the laws defined in cats.laws.ApplicativeLaws.
*/
@typeclass trait Applicative[F[_]] extends Apply[F] { self =>
@typeclass trait Applicative[F[_]] extends Apply[F] with InvariantMonoidal[F] { self =>

/**
* `pure` lifts any value into the Applicative Functor.
*
* Example:
* {{{
* scala> import cats.implicits._
*
* scala> Applicative[Option].pure(10)
* res0: Option[Int] = Some(10)
* }}}
*/
def pure[A](x: A): F[A]

/**
* Returns an `F[Unit]` value, equivalent with `pure(())`.
Expand Down Expand Up @@ -184,11 +172,14 @@ import simulacrum.typeclass
*/
def whenA[A](cond: Boolean)(f: => F[A]): F[Unit] =
if (cond) void(f) else pure(())

override def monoid[A](implicit A: Monoid[A]): Monoid[F[A]] =
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every time we add a method to a trait, we break binary compatibility. Is there any reason to have this here vs the object? Can you really customize this based on the F[_]?

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Hmm, maybe you are right. We had the same discussion with regards to parallel, but I think in this case it might not be as customizable.

new ApplicativeMonoid[F, A](this, A)
}

object Applicative {
def monoid[F[_], A](implicit f: Applicative[F], monoid: Monoid[A]): Monoid[F[A]] =
new ApplicativeMonoid[F, A](f, monoid)
f.monoid

/**
* Creates an applicative functor for `F`, holding domain fixed and combining
Expand Down
7 changes: 5 additions & 2 deletions core/src/main/scala/cats/Apply.scala
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Expand Up @@ -8,7 +8,7 @@ import simulacrum.typeclass
* Must obey the laws defined in cats.laws.ApplyLaws.
*/
@typeclass(excludeParents = List("ApplyArityFunctions"))
trait Apply[F[_]] extends Functor[F] with Semigroupal[F] with ApplyArityFunctions[F] { self =>
trait Apply[F[_]] extends Functor[F] with InvariantSemigroupal[F] with ApplyArityFunctions[F] { self =>

/**
* Given a value and a function in the Apply context, applies the
Expand Down Expand Up @@ -79,11 +79,14 @@ trait Apply[F[_]] extends Functor[F] with Semigroupal[F] with ApplyArityFunction
val F = self
val G = Apply[G]
}

override def semigroup[A](implicit A: Semigroup[A]): Semigroup[F[A]] =
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same question about customization.

new ApplySemigroup[F, A](this, A)
}

object Apply {
def semigroup[F[_], A](implicit f: Apply[F], sg: Semigroup[A]): Semigroup[F[A]] =
new ApplySemigroup[F, A](f, sg)
f.semigroup
}

private[cats] class ApplySemigroup[F[_], A](f: Apply[F], sg: Semigroup[A]) extends Semigroup[F[A]] {
Expand Down
12 changes: 12 additions & 0 deletions core/src/main/scala/cats/Composed.scala
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Expand Up @@ -136,6 +136,18 @@ private[cats] trait ComposedSemigroupal[F[_], G[_]] extends ContravariantSemigro
}
}

private[cats] trait ComposedInvariantApplySemigroupal[F[_], G[_]] extends InvariantSemigroupal[λ[α => F[G[α]]]] with ComposedInvariantCovariant[F, G] { outer =>
def F: InvariantSemigroupal[F]
def G: Apply[G]

def product[A, B](fa: F[G[A]], fb: F[G[B]]): F[G[(A, B)]] =
F.imap(F.product(fa, fb)) { case (ga, gb) =>
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do you plan to add tests for this instance?

G.map2(ga, gb)(_ -> _)
} { g: G[(A, B)] =>
(G.map(g)(_._1), G.map(g)(_._2))
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This line is not tested, we might need to test an instance that is not a covariant.

}
}

private[cats] trait ComposedCovariantContravariant[F[_], G[_]] extends Contravariant[λ[α => F[G[α]]]] { outer =>
def F: Functor[F]
def G: Contravariant[G]
Expand Down
16 changes: 14 additions & 2 deletions core/src/main/scala/cats/ContravariantMonoidal.scala
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Expand Up @@ -11,12 +11,24 @@ import simulacrum.typeclass
* Based on ekmett's contravariant library:
* https://hackage.haskell.org/package/contravariant-1.4/docs/Data-Functor-Contravariant-Divisible.html
*/
@typeclass trait ContravariantMonoidal[F[_]] extends ContravariantSemigroupal[F] { self =>
@typeclass trait ContravariantMonoidal[F[_]] extends ContravariantSemigroupal[F] with InvariantMonoidal[F] {
/**
* `unit` produces an instance of `F` for any type `A`
* that is trivial with respect to `contramap2` along
* the diagonal
*/
def unit[A]: F[A]

override def pure[A](a: A): F[A] = unit

override def monoid[A](implicit A: Monoid[A]): Monoid[F[A]] =
ContravariantMonoidal.monoid(this)
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this seems to be breaking the previous pattern: we are calling the object from the trait, but in the other cases we call it the opposite direction.

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Yes, this is because we can define a ContravariantMonoidal regardless of if A is a Monoid or not.

}
object ContravariantMonoidal extends SemigroupalArityFunctions {
def monoid[F[_], A](implicit f: ContravariantMonoidal[F]): Monoid[F[A]] =
new ContravariantMonoidalMonoid[F, A](f)
}

private[cats] class ContravariantMonoidalMonoid[F[_], A](f: ContravariantMonoidal[F]) extends ContravariantSemigroupalSemigroup[F, A](f) with Monoid[F[A]] {
def empty: F[A] = f.unit
}
object ContravariantMonoidal extends SemigroupalArityFunctions
16 changes: 14 additions & 2 deletions core/src/main/scala/cats/ContravariantSemigroupal.scala
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Expand Up @@ -6,11 +6,23 @@ import simulacrum.typeclass
* [[ContravariantSemigroupal]] is nothing more than something both contravariant
* and Semigroupal. It comes up enough to be useful, and composes well
*/
@typeclass trait ContravariantSemigroupal[F[_]] extends Semigroupal[F] with Contravariant[F] { self =>
@typeclass trait ContravariantSemigroupal[F[_]] extends InvariantSemigroupal[F] with Contravariant[F] { self =>
override def composeFunctor[G[_]: Functor]: ContravariantSemigroupal[λ[α => F[G[α]]]] =
new ComposedSemigroupal[F, G] {
def F = self
def G = Functor[G]
}

override def semigroup[A](implicit A: Semigroup[A]): Semigroup[F[A]] =
ContravariantSemigroupal.semigroup(this)
}

object ContravariantSemigroupal extends SemigroupalArityFunctions {
def semigroup[F[_], A](implicit f: ContravariantSemigroupal[F]): Semigroup[F[A]] =
new ContravariantSemigroupalSemigroup[F, A](f)
}

private[cats] class ContravariantSemigroupalSemigroup[F[_], A](f: ContravariantSemigroupal[F]) extends Semigroup[F[A]] {
def combine(a: F[A], b: F[A]): F[A] =
ContravariantSemigroupal.contramap2(a, b)((a: A) => (a, a))(f, f)
}
object ContravariantSemigroupal extends SemigroupalArityFunctions
25 changes: 24 additions & 1 deletion core/src/main/scala/cats/InvariantMonoidal.scala
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Expand Up @@ -7,6 +7,29 @@ import simulacrum.typeclass
*
* Must obey the laws defined in cats.laws.InvariantMonoidalLaws.
*/
@typeclass trait InvariantMonoidal[F[_]] extends Invariant[F] with Semigroupal[F] {
@typeclass trait InvariantMonoidal[F[_]] extends InvariantSemigroupal[F] {
/**
* `pure` lifts any value into a Monoidal Functor.
*
* Example:
* {{{
* scala> import cats.implicits._
*
* scala> InvariantMonoidal[Option].pure(10)
* res0: Option[Int] = Some(10)
* }}}
*/
def pure[A](a: A): F[A]

/**
* Gives a `Monoid` instance if A itself has a `Monoid` instance.
*/
def monoid[A](implicit A: Monoid[A]): Monoid[F[A]] =
new InvariantMonoidalMonoid[F, A](this, A)

}


private[cats] class InvariantMonoidalMonoid[F[_], A](f: InvariantMonoidal[F], monoid: Monoid[A]) extends InvariantSemigroupalSemigroup(f, monoid) with Monoid[F[A]] {
def empty: F[A] = f.pure(monoid.empty)
}
30 changes: 30 additions & 0 deletions core/src/main/scala/cats/InvariantSemigroupal.scala
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@@ -0,0 +1,30 @@
package cats

import simulacrum.typeclass

/**
* [[InvariantSemigroupal]] is nothing more than something both invariant
* and Semigroupal. It comes up enough to be useful, and composes well
*/
@typeclass trait InvariantSemigroupal[F[_]] extends Semigroupal[F] with Invariant[F] { self =>

def composeApply[G[_]: Apply]: InvariantSemigroupal[λ[α => F[G[α]]]] =
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Any plan to test cover this one as well?

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Has this been addressed?

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Yep!

new ComposedInvariantApplySemigroupal[F, G] {
def F = self
def G = Apply[G]
}

/**
* Gives a `Semigroup` instance if A itself has a `Semigroup` instance.
*/
def semigroup[A](implicit A: Semigroup[A]): Semigroup[F[A]] =
new InvariantSemigroupalSemigroup[F, A](this, A)

}

object InvariantSemigroupal extends SemigroupalArityFunctions

private[cats] class InvariantSemigroupalSemigroup[F[_], A](f: InvariantSemigroupal[F], sg: Semigroup[A]) extends Semigroup[F[A]] {
def combine(a: F[A], b: F[A]): F[A] =
InvariantSemigroupal.imap2(a, b)(sg.combine)(a => (a, a))(f, f)
}
9 changes: 1 addition & 8 deletions core/src/main/scala/cats/Semigroupal.scala
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Expand Up @@ -16,11 +16,4 @@ import simulacrum.typeclass
def product[A, B](fa: F[A], fb: F[B]): F[(A, B)]
}

object Semigroupal extends SemigroupalArityFunctions {
implicit def catsSemigroupalForMonoid: Semigroupal[Monoid] = new Semigroupal[Monoid] {
def product[A, B](fa: Monoid[A], fb: Monoid[B]): Monoid[(A, B)] = new Monoid[(A, B)] {
val empty = fa.empty -> fb.empty
def combine(x: (A, B), y: (A, B)): (A, B) = fa.combine(x._1, y._1) -> fb.combine(x._2, y._2)
}
}
}
object Semigroupal extends SemigroupalArityFunctions
23 changes: 20 additions & 3 deletions core/src/main/scala/cats/data/Nested.scala
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Expand Up @@ -142,27 +142,34 @@ private[data] sealed abstract class NestedInstances8 extends NestedInstances9 {
}

private[data] sealed abstract class NestedInstances9 extends NestedInstances10 {
implicit def catsDataInvariantSemigroupalApplyForNested[F[_]: InvariantSemigroupal, G[_]: Apply]: InvariantSemigroupal[Nested[F, G, ?]] =
new NestedInvariantSemigroupalApply[F, G] {
val FG: InvariantSemigroupal[λ[α => F[G[α]]]] = InvariantSemigroupal[F].composeApply[G]
}
}

private[data] sealed abstract class NestedInstances10 extends NestedInstances11 {
implicit def catsDataFunctorForNested[F[_]: Functor, G[_]: Functor]: Functor[Nested[F, G, ?]] =
new NestedFunctor[F, G] {
val FG: Functor[λ[α => F[G[α]]]] = Functor[F].compose[G]
}
}

private[data] sealed abstract class NestedInstances10 extends NestedInstances11 {
private[data] sealed abstract class NestedInstances11 extends NestedInstances12 {
implicit def catsDataInvariantForNested[F[_]: Invariant, G[_]: Invariant]: Invariant[Nested[F, G, ?]] =
new NestedInvariant[F, G] {
val FG: Invariant[λ[α => F[G[α]]]] = Invariant[F].compose[G]
}
}

private[data] sealed abstract class NestedInstances11 extends NestedInstances12 {
private[data] sealed abstract class NestedInstances12 extends NestedInstances13 {
implicit def catsDataInvariantForCovariantNested[F[_]: Invariant, G[_]: Functor]: Invariant[Nested[F, G, ?]] =
new NestedInvariant[F, G] {
val FG: Invariant[λ[α => F[G[α]]]] = Invariant[F].composeFunctor[G]
}
}

private[data] sealed abstract class NestedInstances12 {
private[data] sealed abstract class NestedInstances13 {
implicit def catsDataInvariantForNestedContravariant[F[_]: Invariant, G[_]: Contravariant]: Invariant[Nested[F, G, ?]] =
new NestedInvariant[F, G] {
val FG: Invariant[λ[α => F[G[α]]]] = Invariant[F].composeContravariant[G]
Expand Down Expand Up @@ -280,3 +287,13 @@ private[data] trait NestedContravariantMonoidal[F[_], G[_]] extends Contravarian
def product[A, B](fa: Nested[F, G, A], fb: Nested[F, G, B]): Nested[F, G, (A, B)] =
Nested(FG.product(fa.value, fb.value))
}

private[data] trait NestedInvariantSemigroupalApply[F[_], G[_]] extends InvariantSemigroupal[Nested[F, G, ?]] {
def FG: InvariantSemigroupal[λ[α => F[G[α]]]]

def imap[A, B](fa: Nested[F, G, A])(f: A => B)(g: B => A): Nested[F, G, B] =
Nested(FG.imap(fa.value)(f)(g))

def product[A, B](fa: Nested[F, G, A], fb: Nested[F, G, B]): Nested[F, G, (A, B)] =
Nested(FG.product(fa.value, fb.value))
}
15 changes: 14 additions & 1 deletion core/src/main/scala/cats/instances/invariant.scala
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@@ -1,10 +1,23 @@
package cats.instances

import cats.kernel._
import cats.InvariantMonoidal
import cats.{InvariantMonoidal, Monoid, InvariantSemigroupal}

trait InvariantMonoidalInstances {

implicit def catsSemigroupalForMonoid: InvariantSemigroupal[Monoid] = new InvariantSemigroupal[Monoid] {
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I am curious why not move these two to the companion of Monoid and Semigroup to avoid a required import?

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Because they're in kernel :/

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oh Duh

def product[A, B](fa: Monoid[A], fb: Monoid[B]): Monoid[(A, B)] = new Monoid[(A, B)] {
val empty = fa.empty -> fb.empty
def combine(x: (A, B), y: (A, B)): (A, B) = fa.combine(x._1, y._1) -> fb.combine(x._2, y._2)
}

def imap[A, B](fa: Monoid[A])(f: A => B)(g: B => A): Monoid[B] = new Monoid[B] {
def empty: B = f(fa.empty)

def combine(x: B, y: B): B = f(fa.combine(g(x), g(y)))
}
}

implicit val catsInvariantMonoidalSemigroup: InvariantMonoidal[Semigroup] = new InvariantMonoidal[Semigroup] {
def product[A, B](fa: Semigroup[A], fb: Semigroup[B]): Semigroup[(A, B)] = new Semigroup[(A, B)] {
def combine(x: (A, B), y: (A, B)): (A, B) = fa.combine(x._1, y._1) -> fb.combine(x._2, y._2)
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