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Simple & Efficient data access for Scala and Scala.js

There is a newer version: 0.5.0

/*
 * Copyright 2016 47 Degrees, LLC. 
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package cats.free

import cats.{Id, ~>}
import cats.data.Coproduct

import scala.annotation.tailrec

object FreeTopExt {

  @tailrec
  def inspect[F[_]](free: Free[F, _]): Option[F[_]] = free match {
    case Free.Pure(p)              => None
    case Free.Suspend(fa)          => Some(fa)
    case Free.FlatMapped(free2, _) => inspect(free2)
  }

  /**
    * Is the first step a `Pure` ?
    *
    * Could be implemented using `resume` as :
    * {{{
    * val liftCoyoneda: F ~> Coyoneda[F, ?] = λ[(F ~> Coyoneda[F, ?])](Coyoneda.lift(_))
    * free.compile[Coyoneda[F, ?]](liftCoyoneda).resume.toOption
    * }}}
    */
  def inspectPure[F[_], A](free: Free[F, A]): Option[A] = free match {
    case Free.Pure(p)              => Some(p)
    case Free.Suspend(fa)          => None
    case Free.FlatMapped(free2, _) => None
  }

  def modify[F[_], A](free: Free[F, A])(f: F ~> Coproduct[F, Id, ?]): Free[F, A] =
    free match {
      case pure @ Free.Pure(_)          => pure
      case Free.Suspend(fa)             => f(fa).run.fold(Free.liftF(_), Free.Pure(_))
      case Free.FlatMapped(free2, cont) => Free.FlatMapped(modify(free2)(f), cont).step
    }

  def print[F[_], A](free: Free[F, A]): String = free match {
    case Free.Pure(p)              => s"Pure($p)"
    case Free.Suspend(fa)          => s"Suspend($fa)"
    case Free.FlatMapped(free2, _) => s"FlatMapped(${print(free2)},  Free>)"
  }

}