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feat: +invariantK instance for Mid #1113

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Apr 20, 2023
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
package tofu.higherKind
import cats.data.Chain
import cats.tagless.ApplyK
import cats.{Monoid, MonoidK, Semigroup}
import cats.tagless.{ApplyK, InvariantK}
import cats.{Monoid, MonoidK, Semigroup, ~>}
import tofu.higherKind.Mid.MidCompose
import tofu.syntax.funk.funK

@@ -47,13 +47,22 @@ trait MidInstances extends MidInstances1 {

trait MidInstances1 {
implicit def midAlgebraSemigroup[F[_], U[f[_]]: ApplyK]: Semigroup[U[Mid[F, *]]] = new MidAlgebraSemigroup[F, U]

private val midInvariantInstance: InvariantK[Mid[*[_], Any]] = new MidInvariantK()
implicit def midInvariantK[A]: InvariantK[Mid[*[_], A]] = midInvariantInstance.asInstanceOf[InvariantK[Mid[*[_], A]]]
}

class MidMonoidK[F[_]] extends MonoidK[Mid[F, *]] {
def empty[A]: Mid[F, A] = fa => fa
def combineK[A](x: Mid[F, A], y: Mid[F, A]): Mid[F, A] = fa => x(y(fa))
}

class MidInvariantK extends InvariantK[Mid[*[_], Any]] {
def imapK[F[_], G[_]](af: Mid[F, Any])(fk: F ~> G)(gk: G ~> F): Mid[G, Any] = { ga =>
fk(af(gk(ga)))
}
}

class MidAlgebraMonoid[F[_], U[f[_]]: MonoidalK] extends MidAlgebraSemigroup[F, U] with Monoid[U[Mid[F, *]]] {
def empty: U[Mid[F, *]] = Mid.point[F].pureK[U]
}
Original file line number Diff line number Diff line change
@@ -1,13 +1,14 @@
package tofu.higherKind

import cats.tagless.ApplyK
import cats.tagless.{ApplyK, InvariantK}
import cats.{Monoid, Semigroup}
import tofu.higherKind.Mid._

object MidSuite {
def summonMidInstances[F[_], U[_[_]]: ApplyK, W[_[_]]: MonoidalK](): Unit = {
implicitly[Semigroup[U[Mid[F, *]]]]
implicitly[Monoid[W[Mid[F, *]]]]
implicitly[InvariantK[Mid[*[_], Any]]]
()
}
}