scalaz.OptionT.scala Maven / Gradle / Ivy
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package scalaz
import std.option.{optionInstance, none, some}
/**
* OptionT monad transformer.
*/
final case class OptionT[F[_], A](run: F[Option[A]]) {
self =>
def map[B](f: A => B)(implicit F: Functor[F]): OptionT[F, B] = new OptionT[F, B](mapO(_ map f))
def mapT[G[_], B](f: F[Option[A]] => G[Option[B]]): OptionT[G, B] =
OptionT(f(run))
def flatMap[B](f: A => OptionT[F, B])(implicit F: Monad[F]): OptionT[F, B] = new OptionT[F, B](
F.bind(self.run) {
case None => F.point(None: Option[B])
case Some(z) => f(z).run
}
)
def mapF[B](f: A => F[B])(implicit F: Monad[F]): OptionT[F, B] = new OptionT[F, B](
F.bind(self.run) {
case None => F.point(none[B])
case Some(z) => F.map(f(z))(b => some(b))
}
)
def flatMapF[B](f: A => F[Option[B]])(implicit F: Monad[F]): OptionT[F, B] = new OptionT[F, B](
F.bind(self.run) {
case None => F.point(none[B])
case Some(z) => f(z)
}
)
def foldRight[Z](z: => Z)(f: (A, => Z) => Z)(implicit F: Foldable[F]): Z = {
import std.option._
F.foldRight[Option[A], Z](run, z)((a, b) => Foldable[Option].foldRight[A, Z](a, b)(f))
}
def traverse[G[_], B](f: A => G[B])(implicit F: Traverse[F], G: Applicative[G]): G[OptionT[F, B]] = {
import std.option._
G.map(F.traverse(run)(o => Traverse[Option].traverse(o)(f)))(OptionT(_))
}
def ap[B](f: => OptionT[F, A => B])(implicit F: Monad[F]): OptionT[F, B] =
OptionT(F.bind(f.run){
case None => F.point(None)
case Some(ff) => F.map(run)(_ map ff)
})
/** Apply a function in the environment of both options, containing
* both `F`s. It is not compatible with `Monad#bind`.
*/
def app[B](f: => OptionT[F, A => B])(implicit F: Apply[F]): OptionT[F, B] =
OptionT(F.apply2(f.run, run) {
case (ff, aa) => optionInstance.ap(aa)(ff)
})
def isDefined(implicit F: Functor[F]): F[Boolean] = mapO(_.isDefined)
def isEmpty(implicit F: Functor[F]): F[Boolean] = mapO(_.isEmpty)
def filter(f: A => Boolean)(implicit F: Functor[F]): OptionT[F, A] = OptionT(F.map(self.run) { _ filter f })
def fold[X](some: A => X, none: => X)(implicit F: Functor[F]): F[X] =
mapO {
case None => none
case Some(a) => some(a)
}
def getOrElse(default: => A)(implicit F: Functor[F]): F[A] = mapO(_.getOrElse(default))
/** Alias for `getOrElse`. */
def |(default: => A)(implicit F: Functor[F]): F[A] = getOrElse(default)
def getOrElseF(default: => F[A])(implicit F: Monad[F]): F[A] =
F.bind(self.run) {
case None => default
case Some(a) => F.point(a)
}
def orZero(implicit F0: Functor[F], M0: Monoid[A]): F[A] = getOrElse(M0.zero)
def unary_~(implicit F0: Functor[F], M0: Monoid[A]): F[A] = orZero
def exists(f: A => Boolean)(implicit F: Functor[F]): F[Boolean] = mapO(_.exists(f))
def forall(f: A => Boolean)(implicit F: Functor[F]): F[Boolean] = mapO(_.forall(f))
def orElse(a: => OptionT[F, A])(implicit F: Monad[F]): OptionT[F, A] =
OptionT(F.bind(run) {
case None => a.run
case x@Some(_) => F.point(x)
})
def |||(a: => OptionT[F, A])(implicit F: Monad[F]): OptionT[F, A] =
orElse(a)
/** @since 7.0.3 */
def toRight[E](e: => E)(implicit F: Functor[F]): EitherT[E, F, A] = EitherT(F.map(run)(std.option.toRight(_)(e)))
def toListT(implicit F: Functor[F]) : ListT[F, A] = ListT[F,A](F.map(run)(IList.fromOption))
/** @since 7.0.3 */
def toLeft[B](b: => B)(implicit F: Functor[F]): EitherT[A, F, B] = EitherT(F.map(run)(std.option.toLeft(_)(b)))
private def mapO[B](f: Option[A] => B)(implicit F: Functor[F]) = F.map(run)(f)
}
//
// Prioritized Implicits for type class instances
//
sealed abstract class OptionTInstances3 {
implicit def optionTFunctor[F[_]](implicit F0: Functor[F]): Functor[OptionT[F, *]] =
new OptionTFunctor[F] {
override def F: Functor[F] = F0
}
}
sealed abstract class OptionTInstances2 extends OptionTInstances3 {
implicit def optionTBindRec[F[_]](implicit F0: Monad[F], B0: BindRec[F]): BindRec[OptionT[F, *]] =
new OptionTBindRec[F] {
override def F = F0
override def B = B0
}
}
sealed abstract class OptionTInstances1 extends OptionTInstances2 {
implicit def optionTFoldable[F[_]](implicit F0: Foldable[F]): Foldable[OptionT[F, *]] =
new OptionTFoldable[F] {
override def F: Foldable[F] = F0
}
implicit def optionTMonadError[F[_], E](implicit F0: MonadError[F, E]): MonadError[OptionT[F, *], E] =
new OptionTMonadError[F, E] {
def F = F0
}
implicit def optionTAlt[F[_]](implicit F0: Monad[F]): Alt[OptionT[F, *]] =
new Alt[OptionT[F, *]] with OptionTApply[F] with OptionTPoint[F] {
override def F: Monad[F] = F0
def alt[A](a: => OptionT[F, A], b: => OptionT[F, A]): OptionT[F, A] = a orElse b
}
}
sealed abstract class OptionTInstances0 extends OptionTInstances1 {
implicit def optionTMonadPlus[F[_]](implicit F0: Monad[F]): MonadPlus[OptionT[F, *]] =
new OptionTMonadPlus[F] {
override def F: Monad[F] = F0
}
}
sealed abstract class OptionTInstances extends OptionTInstances0 {
implicit val optionTMonadTrans: Hoist[OptionT] = new OptionTHoist {}
implicit def optionTTraverse[F[_]](implicit F0: Traverse[F]): Traverse[OptionT[F, *]] =
new OptionTTraverse[F] {
override def F: Traverse[F] = F0
}
implicit def optionTEqual[F[_], A](implicit F0: Equal[F[Option[A]]]): Equal[OptionT[F, A]] =
F0.contramap((_: OptionT[F, A]).run)
implicit def optionTShow[F[_], A](implicit F0: Show[F[Option[A]]]): Show[OptionT[F, A]] =
Contravariant[Show].contramap(F0)(_.run)
implicit def optionTDecidable[F[_]](implicit F0: Divisible[F]): Decidable[OptionT[F, *]] =
new OptionTDecidable[F] {
override def F: Divisible[F] = F0
}
}
object OptionT extends OptionTInstances {
def optionT[M[_]]: λ[α => M[Option[α]]] ~> OptionT[M, *] =
new (λ[α => M[Option[α]]] ~> OptionT[M, *]) {
def apply[A](a: M[Option[A]]) = new OptionT[M, A](a)
}
def some[M[_], A](v: => A)(implicit M: Applicative[M]): OptionT[M, A] =
OptionT.optionT[M].apply[A](M.point(Some(v)))
def none[M[_], A](implicit M: Applicative[M]): OptionT[M, A] =
OptionT.optionT[M].apply[A](M.point(None))
def monadTell[F[_], W, A](implicit MT0: MonadTell[F, W]): MonadTell[OptionT[F, *], W] =
new OptionTMonadTell[F, W] {
def MT = MT0
}
def monadListen[F[_], W, A](implicit ML0: MonadListen[F, W]): MonadListen[OptionT[F, *], W] =
new OptionTMonadListen[F, W] {
def MT = ML0
}
}
//
// Implementation traits for type class instances
//
private trait OptionTDecidable[F[_]] extends Decidable[OptionT[F, *]] {
implicit def F: Divisible[F]
override final def conquer[A]: OptionT[F, A] = OptionT(F.conquer)
override final def divide2[A1, A2, Z](a1: => OptionT[F, A1], a2: => OptionT[F, A2])(f: Z => (A1, A2)): OptionT[F, Z] =
OptionT(F.divide2(a1.run, a2.run)(z => Unzip[Option].unzip(z.map(f))))
override final def choose2[Z, A1, A2](a1: => OptionT[F, A1], a2: => OptionT[F, A2])(f: Z => A1 \/ A2): OptionT[F, Z] =
OptionT(
F.divide2(a1.run, a2.run)(_.map(f)
.fold[(Option[A1], Option[A2])]((Option.empty, Option.empty))(
_.fold(a1 => (Some(a1), Option.empty), a2 => (Option.empty, Some(a2)))
))
)
}
private trait OptionTFunctor[F[_]] extends Functor[OptionT[F, *]] {
implicit def F: Functor[F]
override def map[A, B](fa: OptionT[F, A])(f: A => B): OptionT[F, B] = fa map f
}
private trait OptionTApply[F[_]] extends Apply[OptionT[F, *]] with OptionTFunctor[F]{
implicit def F: Monad[F]
override final def ap[A, B](fa: => OptionT[F, A])(f: => OptionT[F, A => B]): OptionT[F, B] = fa ap f
}
private trait OptionTPoint[F[_]] {
implicit def F: Applicative[F]
def point[A](a: => A): OptionT[F, A] = OptionT[F, A](F.point(some(a)))
}
private trait OptionTBind[F[_]] extends Bind[OptionT[F, *]] with OptionTFunctor[F]{
implicit def F: Monad[F]
final def bind[A, B](fa: OptionT[F, A])(f: A => OptionT[F, B]): OptionT[F, B] = fa flatMap f
}
private trait OptionTBindRec[F[_]] extends BindRec[OptionT[F, *]] with OptionTBind[F] {
implicit def F: Monad[F]
implicit def B: BindRec[F]
final def tailrecM[A, B](a: A)(f: A => OptionT[F, A \/ B]): OptionT[F, B] =
OptionT(
B.tailrecM[A, Option[B]](a)(a0 => F.map(f(a0).run) {
_.fold(\/.right[A, Option[B]](None: Option[B]))(_.map(Some.apply))
})
)
}
private trait OptionTMonad[F[_]] extends Monad[OptionT[F, *]] with OptionTBind[F] with OptionTPoint[F] {
implicit def F: Monad[F]
}
private trait OptionTMonadError[F[_], E] extends MonadError[OptionT[F, *], E] with OptionTMonad[F] {
override def F: MonadError[F, E]
override def raiseError[A](e: E) =
OptionT[F, A](F.map(F.raiseError[A](e))(Some(_)))
override def handleError[A](fa: OptionT[F, A])(f: E => OptionT[F, A]) =
OptionT[F, A](F.handleError(fa.run)(f(_).run))
}
private trait OptionTFoldable[F[_]] extends Foldable.FromFoldr[OptionT[F, *]] {
implicit def F: Foldable[F]
override def foldRight[A, B](fa: OptionT[F, A], z: => B)(f: (A, => B) => B): B = fa.foldRight(z)(f)
}
private trait OptionTTraverse[F[_]] extends Traverse[OptionT[F, *]] with OptionTFoldable[F] with OptionTFunctor[F]{
implicit def F: Traverse[F]
def traverseImpl[G[_] : Applicative, A, B](fa: OptionT[F, A])(f: A => G[B]): G[OptionT[F, B]] = fa traverse f
}
private trait OptionTHoist extends Hoist[OptionT] {
def liftM[G[_], A](a: G[A])(implicit G: Monad[G]): OptionT[G, A] =
OptionT[G, A](G.map[A, Option[A]](a)((a: A) => some(a)))
def hoist[M[_]: Monad, N[_]](f: M ~> N): OptionT[M, *] ~> OptionT[N, *] =
new (OptionT[M, *] ~> OptionT[N, *]) {
def apply[A](fa: OptionT[M, A]): OptionT[N, A] =
fa.mapT(f.apply)
}
implicit def apply[G[_] : Monad]: Monad[OptionT[G, *]] = OptionT.optionTMonadPlus[G]
}
private trait OptionTMonadPlus[F[_]] extends MonadPlus[OptionT[F, *]] with OptionTMonad[F] {
implicit def F: Monad[F]
def empty[A]: OptionT[F, A] = OptionT(F point none[A])
def plus[A](a: OptionT[F, A], b: => OptionT[F, A]): OptionT[F, A] = a orElse b
}
private trait OptionTMonadTell[F[_], W] extends MonadTell[OptionT[F, *], W] with OptionTMonad[F] with OptionTHoist {
def MT: MonadTell[F, W]
implicit def F: Monad[F] = MT
def writer[A](w: W, v: A): OptionT[F, A] =
liftM[F, A](MT.writer(w, v))
}
private trait OptionTMonadListen[F[_], W] extends MonadListen[OptionT[F, *], W] with OptionTMonadTell[F, W] {
def MT: MonadListen[F, W]
def listen[A](ma: OptionT[F, A]): OptionT[F, (A, W)] = {
val tmp = MT.bind[(Option[A], W), Option[(A, W)]](MT.listen(ma.run)) {
case (None, _) => MT.point(None)
case (Some(a), w) => MT.point(Some((a, w)))
}
OptionT.optionT[F].apply[(A, W)](tmp)
}
}
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