/core/src/main/scala/scalaz/StreamT.scala
http://github.com/scalaz/scalaz · Scala · 371 lines · 266 code · 73 blank · 32 comment · 12 complexity · 5cd376029e46cfec4eb2b73f22a2142c MD5 · raw file
- package scalaz
- import Id._
- /**
- * StreamT monad transformer.
- */
- sealed class StreamT[M[_], A](val step: M[StreamT.Step[A, StreamT[M, A]]]) {
- import StreamT._
- def uncons(implicit M: Monad[M]): M[Option[(A, StreamT[M, A])]] =
- M.bind(step) {
- case Yield(a, s) => M.point(Some((a, s())))
- case Skip(s) => s().uncons
- case Done() => M.point(None)
- }
- def unconsRec(implicit M: BindRec[M]): M[Option[(A, StreamT[M, A])]] =
- M.tailrecM(this)(s =>
- M.map(s.step) {
- case Yield(a, s1) => \/-(Some((a, s1())))
- case Skip(s1) => -\/(s1())
- case Done() => \/-(None)
- })
- def ::(a: A)(implicit M: Applicative[M]): StreamT[M, A] = StreamT[M, A](M.point(Yield(a, this)))
- def isEmpty(implicit M: Monad[M]): M[Boolean] = M.map(uncons)(_.isEmpty)
- def isEmptyRec(implicit M: BindRec[M]): M[Boolean] = M.map(unconsRec)(_.isEmpty)
- def head(implicit M: Monad[M]): M[A] = M.map(uncons)(_.getOrElse(sys.error("head: empty StreamT"))._1)
- def headRec(implicit M: BindRec[M]): M[A] = M.map(unconsRec)(_.getOrElse(sys.error("head: empty StreamT"))._1)
- def headOption(implicit M: Monad[M]): M[Option[A]] = M.map(uncons)(_.map(_._1))
- def headOptionRec(implicit M: BindRec[M]): M[Option[A]] = M.map(unconsRec)(_.map(_._1))
- def tailM(implicit M: Monad[M]): M[StreamT[M, A]] = M.map(uncons)(_.getOrElse(sys.error("tailM: empty StreamT"))._2)
- def tailMRec(implicit M: BindRec[M]): M[StreamT[M, A]] = M.map(unconsRec)(_.getOrElse(sys.error("tailM: empty StreamT"))._2)
- def tailOption(implicit M: Monad[M]): M[Option[StreamT[M, A]]] =
- M.map(uncons)(_.map(_._2))
- def tailOptionRec(implicit M: BindRec[M]): M[Option[StreamT[M, A]]] =
- M.map(unconsRec)(_.map(_._2))
- def trans[N[_]](t: M ~> N)(implicit M: Functor[M], N: Functor[N]): StreamT[N, A] =
- StreamT(t(M.map[Step[A, StreamT[M, A]], Step[A, StreamT[N, A]]](this.step) {
- case Yield(a, s) => Yield(a, s() trans t)
- case Skip(s) => Skip(s() trans t)
- case Done() => Done()
- }))
- def filter(p: A => Boolean)(implicit m: Functor[M]): StreamT[M, A] = stepMap[A] {
- case Yield(a, s) => if (p(a)) Yield(a, s() filter p) else Skip(s() filter p)
- case Skip(s) => Skip(s() filter p)
- case Done() => Done()
- }
- def drop(n: Int)(implicit M: Functor[M]): StreamT[M, A] = stepMap[A] {
- case Yield(a, s) => if (n > 0) Skip(s() drop (n - 1)) else Yield(a, s)
- case Skip(s) => Skip(s() drop n)
- case Done() => Done()
- }
- def dropWhile(p: A => Boolean)(implicit m: Functor[M]): StreamT[M, A] = stepMap[A] {
- case Yield(a, s) => if (p(a)) Skip(s() dropWhile p) else Yield(a, s)
- case Skip(s) => Skip(s() dropWhile p)
- case Done() => Done()
- }
- def take(n: Int)(implicit M: Functor[M]): StreamT[M, A] = stepMap[A] {
- case Yield(a, s) => if (n <= 0) Done() else Yield(a, s() take (n - 1))
- case Skip(s) => Skip(s() take n)
- case Done() => Done()
- }
- def takeWhile(p: A => Boolean)(implicit m: Functor[M]): StreamT[M, A] = stepMap[A] {
- case Yield(a, s) => if (p(a)) Yield(a, s() takeWhile p) else Done()
- case Skip(s) => Skip(s() takeWhile p)
- case Done() => Done()
- }
- def ++(bs: => StreamT[M, A])(implicit m: Functor[M]): StreamT[M, A] = stepMap[A] {
- case Yield(a, s) => Yield(a, s() ++ bs)
- case Skip(s) => Skip(s() ++ bs)
- case Done() => Skip(bs)
- }
- def flatMap[B](f: A => StreamT[M, B])(implicit m: Functor[M]): StreamT[M, B] = stepMap[B] {
- case Yield(a, s) => Skip(f(a) ++ (s() flatMap f))
- case Skip(s) => Skip(s() flatMap f)
- case Done() => Done()
- }
- def map[B](f: A => B)(implicit m: Functor[M]): StreamT[M, B] = stepMap[B] {
- case Yield(a, s) => Yield(f(a), s() map f)
- case Skip(s) => Skip(s() map f)
- case Done() => Done()
- }
- /** @since 7.0.1 */
- def mapM[B](f: A => M[B])(implicit M: Monad[M]): StreamT[M, B] = stepBind[B] {
- case Yield(a, s) => M.map(f(a))(Yield(_, s() mapM f))
- case Skip(s) => M.point(Skip(s() mapM f))
- case Done() => M.point(Done())
- }
- def foldLeft[B](z: B)(f: (B, A) => B)(implicit M: Monad[M]): M[B] =
- M.bind(step) {
- case Yield(a, s) => s().foldLeft(f(z, a))(f)
- case Skip(s) => s().foldLeft(z)(f)
- case Done() => M.point(z)
- }
- def foldLeftRec[B](z: B)(f: (B, A) => B)(implicit M: BindRec[M]): M[B] =
- M.tailrecM((() => this, z))(sb => M.map(sb._1().step) {
- case Yield(a, s) => -\/((s, f(sb._2, a)))
- case Skip(s) => -\/((s, sb._2))
- case Done() => \/-(sb._2)
- })
- /**
- * **Warning:** Requires evaluation of the whole stream. Depending on
- * the monad `M`, the evaluation will happen either immediately, or
- * will be deferred until the resulting `LazyList` is extracted from the
- * returned `M`.
- */
- def toLazyList(implicit M: Monad[M]): M[LazyList[A]] = M.map(rev)(_.reverse)
- /**
- * **Warning:** Requires evaluation of the whole stream. Depending on
- * the monad `M`, the evaluation will happen either immediately, or
- * will be deferred until the resulting `LazyList` is extracted from the
- * returned `M`.
- */
- def toLazyListRec(implicit M: BindRec[M]): M[LazyList[A]] = M.map(revRec)(_.reverse)
- /**
- * Converts this `StreamT` to a lazy `LazyList`, i.e. without forcing
- * evaluation of all elements. Note, however, that at least one element
- * of this stream will be evaluated, and depending on the structure of
- * this stream, up to two elements might be evaluated.
- */
- def asLazyList(implicit ev: M[Step[A, StreamT[M, A]]] === Id[Step[A, StreamT[Id, A]]]): LazyList[A] = {
- def go(s: StreamT[Id, A]): LazyList[A] = s.unconsRec match {
- case None => LazyList.empty[A]
- case Some((a, s1)) => LazyList.cons(a, go(s1))
- }
- go(StreamT(ev(step)))
- }
- def foldRight[B](z: => B)(f: (=> A, => B) => B)(implicit M: Monad[M]): M[B] =
- M.map(rev) {
- _.foldLeft(z)((a, b) => f(b, a))
- }
- def foldRightRec[B](z: => B)(f: (=> A, => B) => B)(implicit M: BindRec[M]): M[B] =
- M.map(revRec) {
- _.foldLeft(z)((a, b) => f(b, a))
- }
- /**
- * `foldRight` with potential to terminate early, e.g. on an infinite stream.
- */
- def foldRightM[B](z: => M[B])(f: (=> A, => M[B]) => M[B])(implicit M: Monad[M]): M[B] =
- M.bind(step) {
- case Yield(a, s) => f(a, s().foldRightM(z)(f))
- case Skip(s) => s().foldRightM(z)(f)
- case Done() => z
- }
- def foldMap[B](f: A => B)(implicit M: Foldable[M], B: Monoid[B]): B =
- M.foldMap(step) {
- case Yield(a, s) => B.append(f(a), s().foldMap(f))
- case Skip(s) => s().foldMap(f)
- case Done() => B.zero
- }
- def length(implicit m: Monad[M]): M[Int] =
- foldLeft(0)((c, a) => 1 + c)
- def lengthRec(implicit M: BindRec[M]): M[Int] =
- foldLeftRec(0)((c, a) => 1 + c)
- def foreach(f: A => M[Unit])(implicit M: Monad[M]): M[Unit] = M.bind(step) {
- case Yield(a,s) => M.bind(f(a))(_ => s() foreach f)
- case Skip(s) => s().foreach(f)
- case Done() => M.pure(())
- }
- def foreachRec(f: A => M[Unit])(implicit M: Monad[M], B: BindRec[M]): M[Unit] =
- B.tailrecM(() => this)(s => M.bind(s().step) {
- case Yield(a, s1) => M.map(f(a))(_ => -\/(s1))
- case Skip(s1) => M.pure(-\/(s1))
- case Done() => M.pure(\/-(()))
- })
- private def stepMap[B](f: Step[A, StreamT[M, A]] => Step[B, StreamT[M, B]])(implicit M: Functor[M]): StreamT[M, B] = StreamT(M.map(step)(f))
- private def stepBind[B](f: Step[A, StreamT[M, A]] => M[Step[B, StreamT[M, B]]])(implicit M: Monad[M]): StreamT[M, B] = StreamT(M.bind(step)(f))
- private def rev(implicit M: Monad[M]): M[LazyList[A]] = {
- def loop(xs: StreamT[M, A], ys: LazyList[A]): M[LazyList[A]] =
- M.bind(xs.step) {
- case Yield(a, s) => loop(s(), a #:: ys)
- case Skip(s) => loop(s(), ys)
- case Done() => M.point(ys)
- }
- loop(this, LazyList.empty)
- }
- private def revRec(implicit M: BindRec[M]): M[LazyList[A]] =
- M.tailrecM((() => this, LazyList.empty[A])) { case (xs, ys) =>
- M.map(xs().step) {
- case Yield(a, s) => -\/((s, a #:: ys))
- case Skip(s) => -\/((s, ys))
- case Done() => \/-(ys)
- }
- }
- }
- //
- // Prioritized Implicits for type class instances
- //
- sealed abstract class StreamTInstances0 {
- implicit def StreamTInstance1[F[_]](implicit F0: Functor[F]): Bind[StreamT[F, *]] with Plus[StreamT[F, *]] =
- new StreamTInstance1[F] {
- implicit def F: Functor[F] = F0
- }
- implicit def StreamTSemigroup[F[_], A](implicit F0: Functor[F]): Semigroup[StreamT[F, A]] =
- new StreamTSemigroup[F, A] {
- implicit def F: Functor[F] = F0
- }
- }
- sealed abstract class StreamTInstances extends StreamTInstances0 {
- implicit def StreamTMonoid[F[_], A](implicit F0: Applicative[F]): Monoid[StreamT[F, A]] =
- new StreamTMonoid[F, A] {
- implicit def F: Applicative[F] = F0
- }
- implicit def StreamTMonadPlus[F[_]](implicit F0: Applicative[F]): MonadPlus[StreamT[F, *]] =
- new StreamTMonadPlus[F] {
- implicit def F: Applicative[F] = F0
- }
- implicit def StreamTEqual[F[_], A](implicit E: Equal[F[LazyList[A]]], F: Monad[F]): Equal[StreamT[F, A]] = E.contramap((_: StreamT[F, A]).toLazyList)
- implicit def StreamTShow[F[_], A](implicit E: Show[F[LazyList[A]]], F: Monad[F]): Show[StreamT[F, A]] = Contravariant[Show].contramap(E)((_: StreamT[F, A]).toLazyList)
- implicit val StreamTHoist: Hoist[StreamT] = new StreamTHoist {}
- implicit def StreamTFoldable[F[_]: Foldable]: Foldable[StreamT[F, *]] =
- new Foldable[StreamT[F, *]] with Foldable.FromFoldMap[StreamT[F, *]] {
- override def foldMap[A, M: Monoid](s: StreamT[F, A])(f: A => M) = s.foldMap(f)
- }
- }
- object StreamT extends StreamTInstances {
- def apply[M[_], A](step: M[Step[A, StreamT[M, A]]]): StreamT[M, A] = new StreamT[M, A](step)
- def empty[M[_], A](implicit M: Applicative[M]): StreamT[M, A] = new StreamT[M, A](M point Done())
- def fromLazyList[M[_], A](mas: M[LazyList[A]])(implicit M: Applicative[M]): StreamT[M, A] = {
- def loop(as: LazyList[A]): Step[A, StreamT[M, A]] = as match {
- case head #:: tail => Yield(head, apply(M.point(loop(tail))))
- case _ => Done()
- }
- apply[M, A](M.map(mas)(loop))
- }
- def unfoldM[M[_],A,B](start: B)(f: B => M[Option[(A,B)]])(implicit M: Functor[M]): StreamT[M,A] =
- StreamT[M,A](M.map(f(start)) {
- case Some((a, b)) => Yield(a, unfoldM(b)(f))
- case None => Done()
- })
- def unfold[A,B](b: B)(f: B => Option[(A,B)]): StreamT[Id,A] = unfoldM[Id,A,B](b)(f)
- def fromIterable[A](s: Iterable[A]): StreamT[Id,A] = {
- def stepper(b: Iterable[A]): Option[(A,Iterable[A])] = if (b.isEmpty) None else Some((b.head, b.tail))
- unfold(s)(stepper)
- }
- def wrapEffect[M[_]:Functor,A](m: M[StreamT[M,A]]): StreamT[M,A] = StreamT(Functor[M].map(m)(Skip(_)))
- def runStreamT[S,A](stream : StreamT[State[S, *],A], s0: S): StreamT[Id,A] =
- StreamT[Id,A]({
- val (a, s) = stream.step(s0)
- s match {
- case Yield(a1, s1) => Yield(a1, runStreamT(s1(), a))
- case Skip(s1) => Skip(runStreamT(s1(), a))
- case Done() => Done()
- }
- })
- sealed abstract class Step[A, S] extends Product with Serializable
- final case class Yield[A, S](a: A, s: () => S) extends Step[A, S]
- object Yield {
- def apply[A, S](a: A, s: => S): Step[A, S] = new Yield(a, () => s)
- }
- final case class Skip[A, S](s: () => S) extends Step[A, S]
- object Skip {
- def apply[A, S](s: => S): Step[A, S] = new Skip(() => s)
- }
- sealed abstract case class Done[A, S]() extends Step[A, S]
- object Done {
- def apply[A, S](): Step[A, S] = done_.asInstanceOf[Done[A, S]]
- // https://github.com/scala/bug/issues/11953
- private[this] final val done_ : Done[Nothing, Nothing] = new Done[Nothing, Nothing]{}
- }
- }
- //
- // Implementation traits for type class instances
- //
- private trait StreamTInstance1[F[_]] extends Bind[StreamT[F, *]] with Plus[StreamT[F, *]] {
- implicit def F: Functor[F]
- override final def map[A, B](fa: StreamT[F, A])(f: A => B) =
- fa map f
- override final def bind[A, B](fa: StreamT[F, A])(f: A => StreamT[F, B]) =
- fa flatMap f
- override final def plus[A](a: StreamT[F, A], b: => StreamT[F, A]) =
- a ++ b
- }
- private trait StreamTSemigroup[F[_], A] extends Semigroup[StreamT[F, A]] {
- implicit def F: Functor[F]
- def append(f1: StreamT[F, A], f2: => StreamT[F, A]): StreamT[F, A] = f1 ++ f2
- }
- private trait StreamTMonoid[F[_], A] extends Monoid[StreamT[F, A]] with StreamTSemigroup[F, A] {
- implicit def F: Applicative[F]
- def zero: StreamT[F, A] = StreamT.empty[F, A]
- }
- private trait StreamTMonadPlus[F[_]] extends MonadPlus[StreamT[F, *]] with StreamTInstance1[F] {
- implicit def F: Applicative[F]
- def point[A](a: => A): StreamT[F, A] = a :: StreamT.empty[F, A]
- def empty[A]: StreamT[F, A] = StreamT.empty
- }
- private trait StreamTHoist extends Hoist[StreamT] {
- import StreamT._
- implicit def apply[G[_] : Monad]: Monad[StreamT[G, *]] = StreamTMonadPlus[G]
- def liftM[G[_], A](a: G[A])(implicit G: Monad[G]): StreamT[G, A] =
- StreamT[G, A](G.map(a)(Yield(_, empty[G, A](G))))
- override def wrapEffect[G[_]: Monad, A](a: G[StreamT[G, A]]): StreamT[G, A] = StreamT.wrapEffect(a)
- def hoist[M[_], N[_]](f: M ~> N)(implicit M: Monad[M]): StreamT[M, *] ~> StreamT[N, *] =
- λ[StreamT[M, *] ~> StreamT[N, *]](a =>
- StreamT(f(M.map(a.step) {
- case Yield(a, s) => Yield(a, hoist(f).apply(s()))
- case Skip(s) => Skip(hoist(f).apply(s()))
- case Done() => Done()
- }
- )))
- }