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/*
 * Copyright 2007 Learning Objects
 *
 * 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 scaloi.misc

import scalaz.Foldable
import scalaz.Id.Id

/** Typeclass evidence for the ability to side-effectively iterate over a container type. */
trait Foreach[F[_]] { self =>
  def foreach[A, U](fa: F[A])(f: A => U): Unit

  /** Composition of foreach over nested types. */
  def compose[G[_]](implicit G: Foreach[G]): Foreach[λ[α => F[G[α]]]] = new Foreach[λ[α => F[G[α]]]] {
    override def foreach[A, U](fa: F[G[A]])(f: A => U): Unit = self.foreach(fa)(ga => G.foreach(ga)(f))
  }
}

object Foreach extends LowPriForeach {
  def apply[F[_]](implicit ev: Foreach[F]): Foreach[F] = ev

  /** Foreach evidence of [[scala.Option]]. */
  implicit def optionForeach: Foreach[Option] = new Foreach[Option] {
    override def foreach[A, U](fa: Option[A])(f: A => U): Unit = fa.foreach(f)
  }

  /** Foreach evidence of [[scala.collection.GenTraversableOnce]]. */
  implicit def gt1Foreach[F[X] <: IterableOnce[X]]: Foreach[F] = new Foreach[F] {
    override def foreach[A, U](fa: F[A])(f: A => U): Unit = fa.iterator.foreach(f)
  }

  /** Foreach evidence of [[scalaz.Id]]. */
  implicit def idForeach: Foreach[Id] = new Foreach[Id] {
    override def foreach[A, U](fa: Id[A])(f: A => U): Unit = f(fa)
  }
}

trait LowPriForeach {

  /** Foreach evidence of a type with [[scalaz.Foldable]] evidence. */
  implicit def foldableForeach[F[_]: Foldable]: Foreach[F] = new Foreach[F] {
    override def foreach[A, U](fa: F[A])(f: A => U): Unit = Foldable[F].foldLeft(fa, ()) {
      case (_, a) => f(a)
    }
  }
}