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• cats-laws_2.10
• 0.3.0
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• ComposeLaws.scala

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

package cats
package laws

import cats.arrow.Compose
import cats.syntax.compose._

/**
 * Laws that must be obeyed by any `cats.arrow.Compose`.
 */
trait ComposeLaws[F[_, _]] {
  implicit def F: Compose[F]

  def composeAssociativity[A, B, C, D](fab: F[A, B], fbc: F[B, C], fcd: F[C, D]): IsEq[F[A, D]] =
    ((fab andThen fbc) andThen fcd) <-> (fab andThen (fbc andThen fcd))
}

object ComposeLaws {
  def apply[F[_, _]](implicit ev: Compose[F]): ComposeLaws[F] =
    new ComposeLaws[F] { def F: Compose[F] = ev }
}