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• 0.3.0
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• InvariantLaws.scala

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cats.laws.InvariantLaws.scala Maven / Gradle / Ivy

package cats
package laws

import cats.functor.Invariant
import cats.syntax.invariant._

/**
 * Laws that must be obeyed by any `cats.functor.Invariant`.
 */
trait InvariantLaws[F[_]] {
  implicit def F: Invariant[F]

  def invariantIdentity[A](fa: F[A]): IsEq[F[A]] =
    fa.imap(identity[A])(identity[A]) <-> fa

  def invariantComposition[A, B, C](fa: F[A], f1: A => B, f2: B => A, g1: B => C, g2: C => B): IsEq[F[C]] =
    fa.imap(f1)(f2).imap(g1)(g2) <-> fa.imap(g1 compose f1)(f2 compose g2)
}

object InvariantLaws {
  def apply[F[_]](implicit ev: Invariant[F]): InvariantLaws[F] =
    new InvariantLaws[F] { def F: Invariant[F] = ev }
}