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package scalaz
package std
import annotation.tailrec
trait ListInstances0 {
implicit def listEqual[A](implicit A0: Equal[A]): Equal[List[A]] = new ListEqual[A] {
implicit def A = A0
}
}
trait ListInstances extends ListInstances0 {
implicit val listInstance = new Traverse[List] with MonadPlus[List] with Each[List] with Index[List] with Length[List] with Zip[List] with Unzip[List] with Align[List] with IsEmpty[List] with Cobind[List] {
def each[A](fa: List[A])(f: A => Unit) = fa foreach f
override def index[A](fa: List[A], i: Int) = fa.lift.apply(i)
// TODO remove after removal of Index
override def indexOr[A](fa: List[A], default: => A, i: Int) = super[Traverse].indexOr(fa, default, i)
override def length[A](fa: List[A]) = fa.length
def point[A](a: => A) = a :: Nil
def bind[A, B](fa: List[A])(f: A => List[B]) = fa flatMap f
def empty[A] = Nil
def plus[A](a: List[A], b: => List[A]) = a ++ b
override def map[A, B](l: List[A])(f: A => B) = l map f
override def filter[A](fa: List[A])(p: A => Boolean): List[A] = fa filter p
def zip[A, B](a: => List[A], b: => List[B]) = {
val _a = a
if(_a.isEmpty) Nil
else _a zip b
}
def unzip[A, B](a: List[(A, B)]) = a.unzip
def alignWith[A, B, C](f: A \&/ B => C) = {
@annotation.tailrec
def loop(aa: List[A], bb: List[B], accum: List[C]): List[C] = (aa, bb) match {
case (Nil, _) =>
accum reverse_::: bb.map(b => f(\&/.That(b)))
case (_, Nil) =>
accum reverse_::: aa.map(a => f(\&/.This(a)))
case (ah :: at, bh :: bt) =>
loop(at, bt, f(\&/.Both(ah, bh)) :: accum)
}
(a, b) => loop(a, b, Nil)
}
def traverseImpl[F[_], A, B](l: List[A])(f: A => F[B])(implicit F: Applicative[F]) = {
// implementation with `foldRight` leads to SOE in:
//
// def wc(c: Char) = State[Boolean, Int]{(inWord) =>
// val s = c != ' '
// (test(!(inWord && s)), s)
// }
// val X = StateT.stateMonad[Boolean].traverse(List[Char]('a'))(wc)
// foldRight(l, F.point(List[B]())) {
// (a, fbs) => F.apply2(f(a), fbs)(_ :: _)
// }
DList.fromList(l).foldr(F.point(List[B]())) {
(a, fbs) => F.apply2(f(a), fbs)(_ :: _)
}
}
override def traverseS[S,A,B](l: List[A])(f: A => State[S,B]): State[S,List[B]] = {
State((s: S) => {
val buf = new collection.mutable.ListBuffer[B]
var cur = s
l.foreach { a => val bs = f(a)(cur); buf += bs._2; cur = bs._1 }
(cur, buf.toList)
})
}
override def foldLeft[A, B](fa: List[A], z: B)(f: (B, A) => B): B = fa.foldLeft(z)(f)
override def foldRight[A, B](fa: List[A], z: => B)(f: (A, => B) => B) = {
import scala.collection.mutable.ArrayStack
val s = new ArrayStack[A]
fa.foreach(a => s += a)
var r = z
while (!s.isEmpty) {
// force and copy the value of r to ensure correctness
val w = r
r = f(s.pop, w)
}
r
}
override def toList[A](fa: List[A]) = fa
def isEmpty[A](fa: List[A]) = fa.isEmpty
def cobind[A, B](fa: List[A])(f: List[A] => B) =
fa match {
case Nil => Nil
case _::t => f(fa) :: cobind(t)(f)
}
override def cojoin[A](a: List[A]) =
a match {
case Nil => Nil
case _::t => a :: cojoin(t)
}
}
implicit def listMonoid[A]: Monoid[List[A]] = new Monoid[List[A]] {
def append(f1: List[A], f2: => List[A]) = f1 ::: f2
def zero: List[A] = Nil
}
implicit def listShow[A: Show]: Show[List[A]] = new Show[List[A]] {
override def show(as: List[A]) = {
def commaSep(rest: List[A], acc: Cord): Cord =
rest match {
case Nil => acc
case x::xs => commaSep(xs, (acc :+ ",") ++ Show[A].show(x))
}
"[" +: (as match {
case Nil => Cord()
case x::xs => commaSep(xs, Show[A].show(x))
}) :+ "]"
}
}
implicit def listOrder[A](implicit A0: Order[A]): Order[List[A]] = new ListOrder[A] {
implicit def A = A0
}
}
trait ListFunctions {
/** Intersperse the element `a` between each adjacent pair of elements in `as` */
final def intersperse[A](as: List[A], a: A): List[A] = {
@tailrec
def intersperse0(accum: List[A], rest: List[A]): List[A] = rest match {
case Nil => accum
case x :: Nil => x :: accum
case h :: t => intersperse0(a :: h :: accum, t)
}
intersperse0(Nil, as).reverse
}
final def tailOption[A](as: List[A]): Option[List[A]] = as match {
case Nil => None
case _ :: t => Some(t)
}
/** [[scala.Nil]] with a sometimes more convenient type */
final def nil[A]: List[A] = Nil
final def toNel[A](as: List[A]): Option[NonEmptyList[A]] = as match {
case Nil => None
case h :: t => Some(NonEmptyList.nel(h, t))
}
final def toZipper[A](as: List[A]): Option[Zipper[A]] =
stream.toZipper(as.toStream)
final def zipperEnd[A](as: List[A]): Option[Zipper[A]] =
stream.zipperEnd(as.toStream)
/**
* Returns `f` applied to the contents of `as` if non-empty, otherwise, the zero element of the `Monoid` for the type `B`.
*/
final def <^>[A, B: Monoid](as: List[A])(f: NonEmptyList[A] => B): B = as match {
case Nil => Monoid[B].zero
case h :: t => f(NonEmptyList.nel(h, t))
}
/** Run `p(a)`s and collect `as` while `p` yields true. Don't run
* any `p`s after the first false.
*/
final def takeWhileM[A, M[_] : Monad](as: List[A])(p: A => M[Boolean]): M[List[A]] = as match {
case Nil => Monad[M].point(Nil)
case h :: t => Monad[M].bind(p(h))(b =>
if (b) Monad[M].map(takeWhileM(t)(p))((tt: List[A]) => h :: tt) else Monad[M].point(Nil))
}
/** Run `p(a)`s and collect `as` while `p` yields false. Don't run
* any `p`s after the first true.
*/
final def takeUntilM[A, M[_] : Monad](as: List[A])(p: A => M[Boolean]): M[List[A]] =
takeWhileM(as)((a: A) => Monad[M].map(p(a))((b) => !b))
final def filterM[A, M[_] : Applicative](as: List[A])(p: A => M[Boolean]): M[List[A]] =
Applicative[M].filterM(as)(p)
/** Run `p(a)`s left-to-right until it yields a true value,
* answering `Some(that)`, or `None` if nothing matched `p`.
*/
final def findM[A, M[_] : Monad](as: List[A])(p: A => M[Boolean]): M[Option[A]] = as match {
case Nil => Monad[M].point(None: Option[A])
case h :: t => Monad[M].bind(p(h))(b =>
if (b) Monad[M].point(Some(h): Option[A]) else findM(t)(p))
}
final def powerset[A](as: List[A]): List[List[A]] = {
import list.listInstance
filterM(as)(_ => true :: false :: Nil)
}
/** A pair of passing and failing values of `as` against `p`. */
final def partitionM[A, M[_]](as: List[A])(p: A => M[Boolean])(implicit F: Applicative[M]): M[(List[A], List[A])] = as match {
case Nil => F.point(Nil: List[A], Nil: List[A])
case h :: t =>
F.ap(partitionM(t)(p))(F.map(p(h))(b => {
case (x, y) => if (b) (h :: x, y) else (x, h :: y)
}))
}
/** A pair of the longest prefix of passing `as` against `p`, and
* the remainder. */
final def spanM[A, M[_] : Monad](as: List[A])(p: A => M[Boolean]): M[(List[A], List[A])] = as match {
case Nil => Monad[M].point(Nil, Nil)
case h :: t =>
Monad[M].bind(p(h))(b =>
if (b) Monad[M].map(spanM(t)(p))((k: (List[A], List[A])) => (h :: k._1, k._2))
else Monad[M].point(Nil, as))
}
/** `spanM` with `p`'s complement. */
final def breakM[A, M[_] : Monad](as: List[A])(p: A => M[Boolean]): M[(List[A], List[A])] =
spanM(as)(a => Monad[M].map(p(a))((b: Boolean) => !b))
@deprecated("use groupWhenM", "7.1")
final def groupByM[A, M[_] : Monad](as: List[A])(p: (A, A) => M[Boolean]): M[List[NonEmptyList[A]]] = groupWhenM(as)(p)
/** Split at each point where `p(as(n), as(n+1))` yields false. */
final def groupWhenM[A, M[_] : Monad](as: List[A])(p: (A, A) => M[Boolean]): M[List[NonEmptyList[A]]] = as match {
case Nil => Monad[M].point(Nil)
case h :: t =>
val stateP = (i: A) => StateT[M, A, Boolean](s => Monad[M].map(p(s, i))(i ->))
Monad[M].bind(spanM[A, ({type λ[α] = StateT[M, A, α]})#λ](t)(stateP).eval(h)) {
case (x, y) =>
Monad[M].map(groupWhenM(y)(p))(g => NonEmptyList.nel(h, x) :: g)
}
}
/** As with the standard library `groupBy` but preserving the fact that the values in the Map must be non-empty */
final def groupBy1[A, B](as: List[A])(f: A => B): Map[B, NonEmptyList[A]] = (Map.empty[B, NonEmptyList[A]] /: as) { (nels, a) =>
val b = f(a)
nels + (b -> (nels get b map (a <:: _) getOrElse NonEmptyList(a)))
} mapValues (_.reverse)
/** `groupWhenM` specialized to [[scalaz.Id.Id]]. */
final def groupWhen[A](as: List[A])(p: (A, A) => Boolean): List[NonEmptyList[A]] = {
@tailrec
def span1(xs: List[A], s: A, l: List[A]): (List[A], List[A]) = xs match {
case Nil => (l, Nil)
case h :: t => if (p(s, h)) span1(t, h, h :: l) else (l, xs)
}
@tailrec
def go(xs: List[A], acc: List[NonEmptyList[A]]): List[NonEmptyList[A]] = xs match {
case Nil => acc.reverse
case h :: t =>
val (x, y) = span1(t, h, Nil)
go(y, NonEmptyList.nel(h, x.reverse) :: acc)
}
go(as, Nil)
}
private[this] def mapAccum[A, B, C](as: List[A])(c: C, f: (C, A) => (C, B)): (C, List[B]) =
as.foldLeft((c, Nil: List[B])){ case ((c, bs), a) =>
val (c0, b) = f(c, a)
(c0, b :: bs)
}
/** All of the `B`s, in order, and the final `C` acquired by a
* stateful left fold over `as`. */
final def mapAccumLeft[A, B, C](as: List[A])(c: C, f: (C, A) => (C, B)): (C, List[B]) = {
val (c0, list) = mapAccum(as)(c, f)
(c0, list.reverse)
}
/** All of the `B`s, in order `as`-wise, and the final `C` acquired
* by a stateful right fold over `as`. */
final def mapAccumRight[A, B, C](as: List[A])(c: C, f: (C, A) => (C, B)): (C, List[B]) =
mapAccum(as.reverse)(c, f)
/** `[as, as.tail, as.tail.tail, ..., Nil]` */
final def tailz[A](as: List[A]): List[List[A]] = as match {
case Nil => Nil :: Nil
case xxs@(_ :: xs) => xxs :: tailz(xs)
}
/** `[Nil, as take 1, as take 2, ..., as]` */
final def initz[A](as: List[A]): List[List[A]] = as match {
case Nil => Nil :: Nil
case xxs@(x :: xs) => Nil :: (initz(xs) map (x :: _))
}
/** Combinations of `as` and `as`, excluding same-element pairs. */
final def allPairs[A](as: List[A]): List[(A, A)] =
tailz(as).tail flatMap (as zip _)
/** `[(as(0), as(1)), (as(1), as(2)), ... (as(size-2), as(size-1))]` */
final def adjacentPairs[A](as: List[A]): List[(A, A)] = as match {
case Nil => Nil
case (_ :: t) => as zip t
}
}
object list extends ListInstances with ListFunctions {
object listSyntax extends scalaz.syntax.std.ToListOps
}
private trait ListEqual[A] extends Equal[List[A]] {
implicit def A: Equal[A]
override def equalIsNatural: Boolean = A.equalIsNatural
override def equal(a1: List[A], a2: List[A]) = (a1 corresponds a2)(Equal[A].equal)
}
private trait ListOrder[A] extends Order[List[A]] with ListEqual[A] {
implicit def A: Order[A]
import Ordering._
@annotation.tailrec
final def order(a1: List[A], a2: List[A]) =
(a1, a2) match {
case (Nil, Nil) => EQ
case (Nil, _::_) => LT
case (_::_, Nil) => GT
case (a::as, b::bs) => Order[A].order(a, b) match {
case EQ => order(as, bs)
case x => x
}
}
}
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