Add NonEmptySet

Author: Luka Jacobowitz

core/src/main/scala/cats/data/NonEmptySet.scala

@@ -0,0 +1,218 @@
+/*
+ * Copyright (c) 2018 Luka Jacobowitz
+ *
+ * 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
+package data
+
+import cats.instances.sortedSet._
+import cats.kernel._
+import cats.{Always, Eq, Eval, Foldable, Later, Now, Reducible, SemigroupK, Show}
+
+import scala.collection.immutable._
+
+final class NonEmptySet[A] private (val set: SortedSet[A]) extends AnyVal {
+
+  private implicit def ordering: Ordering[A] = set.ordering
+  private implicit def order: Order[A] = Order.fromOrdering
+
+  def +(a: A): NonEmptySet[A] = new NonEmptySet(set + a)
+  def ++(as: NonEmptySet[A]): NonEmptySet[A] = concat(as)
+
+  def concat(as: NonEmptySet[A]): NonEmptySet[A] = new NonEmptySet(set ++ as.set)
+
+  def -(a: A): SortedSet[A] = set - a
+  def map[B: Order](f: A ⇒ B): NonEmptySet[B] =
+    new NonEmptySet(SortedSet(set.map(f).to: _*)(Order[B].toOrdering))
+
+  def toNonEmptyList: NonEmptyList[A] = NonEmptyList.fromListUnsafe(set.toList)
+
+  def head: A = set.head
+  def tail: SortedSet[A] = set.tail
+  def last: A = set.last
+
+  def apply(a: A): Boolean = set(a)
+  def contains(a: A): Boolean = set.contains(a)
+
+
+  def union(as: NonEmptySet[A]): NonEmptySet[Ag] = new NonEmptySet(set.union(as.toSet))
+  def size: Int = set.size
+  def forall(p: A ⇒ Boolean): Boolean = set.forall(p)
+  def exists(f: A ⇒ Boolean): Boolean = set.exists(f)
+  def find(f: A ⇒ Boolean): Option[A] = set.find(f)
+  def collect[B](pf: PartialFunction[A, B]): Set[B] = set.collect(pf)
+  def filter(p: A ⇒ Boolean): SortedSet[A] = set.filter(p)
+  def filterNot(p: A ⇒ Boolean): SortedSet[A] = filter(t => !p(t))
+
+
+  /**
+    * Left-associative fold using f.
+    */
+  def foldLeft[B](b: B)(f: (B, A) => B): B =
+    set.foldLeft(b)(f)
+
+  /**
+    * Right-associative fold using f.
+    */
+  def foldRight[B](lb: Eval[B])(f: (A, Eval[B]) => Eval[B]): Eval[B] =
+    Foldable[SortedSet].foldRight(set, lb)(f)
+
+  /**
+    * Left-associative reduce using f.
+    */
+  def reduceLeft(f: (A, A) => A): A =
+    set.reduceLeft(f)
+
+  def reduceLeftTo[B](f: A => B)(g: (B, A) => B): B = {
+    tail.foldLeft(f(head))((b, a) => g(b, a))
+  }
+
+  /**
+    * Left-associative reduce using f.
+    */
+  def reduceRight(f: (A, Eval[A]) => Eval[A]): Eval[A] =
+    reduceRightTo(identity)(f)
+
+  def reduceRightTo[B](f: A => B)(g: (A, Eval[B]) => Eval[B]): Eval[B] =
+    Always((head, tail)).flatMap { case (a, ga) =>
+      Foldable[SortedSet].reduceRightToOption(ga)(f)(g).flatMap {
+        case Some(b) => g(a, Now(b))
+        case None => Later(f(a))
+      }
+    }
+
+  /**
+    * Reduce using the Semigroup of A
+    */
+  def reduce[AA >: A](implicit S: Semigroup[AA]): AA =
+    S.combineAllOption(set).get
+
+  def toSet: SortedSet[A] = set
+
+  /**
+    * Typesafe stringification method.
+    *
+    * This method is similar to .toString except that it stringifies
+    * values according to Show[_] instances, rather than using the
+    * universal .toString method.
+    */
+  def show(implicit A: Show[A]): String =
+    s"NonEmpty${Show[SortedSet[A]].show(set)}"
+
+  /**
+    * Typesafe equality operator.
+    *
+    * This method is similar to == except that it only allows two
+    * NonEmptySet[A] values to be compared to each other, and uses
+    * equality provided by Eq[_] instances, rather than using the
+    * universal equality provided by .equals.
+    */
+  def ===(that: NonEmptySet[A]): Boolean =
+    Eq[SortedSet[A]].eqv(set, that.toSet)
+
+  def length: Int = size
+
+  /**
+    * Zips this `NonEmptySet` with another `NonEmptySet` and applies a function for each pair of elements.
+    *
+    * {{{
+    * scala> import cats.data.NonEmptySet
+    * scala> val as = NonEmptySet.of(1, 2, 3)
+    * scala> val bs = NonEmptySet.of("A", "B", "C")
+    * scala> as.zipWith(bs)(_ + _)
+    * res0: cats.data.NonEmptySet[String] = NonEmptySet(1A, 2B, 3C)
+    * }}}
+    */
+  def zipWith[B, C: Order](b: NonEmptySet[B])(f: (A, B) => C): NonEmptySet[C] =
+    new NonEmptySet(SortedSet((set, b.toSet).zipped.map(f).to: _*)(Order[C].toOrdering))
+
+  def zipWithIndex: NonEmptySet[(A, Int)] =
+    new NonEmptySet(set.zipWithIndex)
+}
+
+private[data] sealed abstract class NonEmptySetInstances {
+  implicit val catsDataInstancesForNonEmptySet: SemigroupK[NonEmptySet] with Reducible[NonEmptySet] =
+    new SemigroupK[NonEmptySet] with Reducible[NonEmptySet] {
+
+      def combineK[A](a: NonEmptySet[A], b: NonEmptySet[A]): NonEmptySet[A] =
+        a ++ b
+
+      override def size[A](fa: NonEmptySet[A]): Long = fa.length.toLong
+
+      override def reduceLeft[A](fa: NonEmptySet[A])(f: (A, A) => A): A =
+        fa.reduceLeft(f)
+
+      override def reduce[A](fa: NonEmptySet[A])(implicit A: Semigroup[A]): A =
+        fa.reduce
+
+      def reduceLeftTo[A, B](fa: NonEmptySet[A])(f: A => B)(g: (B, A) => B): B = fa.reduceLeftTo(f)(g)
+
+      def reduceRightTo[A, B](fa: NonEmptySet[A])(f: A => B)(g: (A, Eval[B]) => Eval[B]): Eval[B] =
+        fa.reduceRightTo(f)(g)
+
+      override def foldLeft[A, B](fa: NonEmptySet[A], b: B)(f: (B, A) => B): B =
+        fa.foldLeft(b)(f)
+
+      override def foldRight[A, B](fa: NonEmptySet[A], lb: Eval[B])(f: (A, Eval[B]) => Eval[B]): Eval[B] =
+        fa.foldRight(lb)(f)
+
+      override def foldMap[A, B](fa: NonEmptySet[A])(f: A => B)(implicit B: Monoid[B]): B =
+        B.combineAll(fa.toSet.iterator.map(f))
+
+      override def fold[A](fa: NonEmptySet[A])(implicit A: Monoid[A]): A =
+        fa.reduce
+
+      override def find[A](fa: NonEmptySet[A])(f: A => Boolean): Option[A] =
+        fa.find(f)
+
+      override def forall[A](fa: NonEmptySet[A])(p: A => Boolean): Boolean =
+        fa.forall(p)
+
+      override def exists[A](fa: NonEmptySet[A])(p: A => Boolean): Boolean =
+        fa.exists(p)
+
+      override def toList[A](fa: NonEmptySet[A]): List[A] = fa.toSet.toList
+
+      override def toNonEmptyList[A](fa: NonEmptySet[A]): NonEmptyList[A] =
+        NonEmptyList(fa.head, fa.tail.toList)
+    }
+
+  implicit def catsDataEqForNonEmptySet[A: Order]: Eq[NonEmptySet[A]] =
+    new Eq[NonEmptySet[A]]{
+      def eqv(x: NonEmptySet[A], y: NonEmptySet[A]): Boolean = x === y
+    }
+
+  implicit def catsDataShowForNonEmptySet[A](implicit A: Show[A]): Show[NonEmptySet[A]] =
+    Show.show[NonEmptySet[A]](_.show)
+
+  implicit def catsDataBandForNonEmptySet[A]: Band[NonEmptySet[A]] = new Band[NonEmptySet[A]] {
+    def combine(x: NonEmptySet[A], y: NonEmptySet[A]): NonEmptySet[A] = x ++ y
+  }
+}
+
+object NonEmptySet extends NonEmptySetInstances {
+  def fromSet[A: Order](as: SortedSet[A]): Option[NonEmptySet[A]] =
+    if (as.nonEmpty) Option(new NonEmptySet(as)) else None
+
+  def fromSetUnsafe[A: Order](set: SortedSet[A]): NonEmptySet[A] =
+    if (set.nonEmpty) new NonEmptySet(set)
+    else throw new IllegalArgumentException("Cannot create NonEmptySet from empty set")
+
+
+  def of[A: Order](a: A, as: A*): NonEmptySet[A] =
+    new NonEmptySet(SortedSet(a)(Order[A].toOrdering) ++ SortedSet(as: _*)(Order[A].toOrdering) + a)
+  def apply[A: Order](head: A, tail: SortedSet[A]): NonEmptySet[A] = new NonEmptySet(SortedSet(head)(Order[A].toOrdering) ++ tail)
+  def one[A: Order](a: A): NonEmptySet[A] = new NonEmptySet(SortedSet(a)(Order[A].toOrdering))
+}

laws/src/main/scala/cats/laws/discipline/Arbitrary.scala

@@ -51,6 +51,13 @@ object arbitrary extends ArbitraryInstances0 {
   implicit def catsLawsCogenForNonEmptyVector[A](implicit A: Cogen[A]): Cogen[NonEmptyVector[A]] =
     Cogen[Vector[A]].contramap(_.toVector)
 
+  implicit def catsLawsArbitraryForNonEmptySet[A: Order](implicit A: Arbitrary[A]): Arbitrary[NonEmptySet[A]] =
+    Arbitrary(implicitly[Arbitrary[SortedSet[A]]].arbitrary.flatMap(fa =>
+      A.arbitrary.map(a => NonEmptySet(a, fa))))
+
+  implicit def catsLawsCogenForNonEmptySet[A: Order: Cogen]: Cogen[NonEmptySet[A]] =
+    Cogen[SortedSet[A]].contramap(_.toSet)
+
   implicit def catsLawsArbitraryForZipVector[A](implicit A: Arbitrary[A]): Arbitrary[ZipVector[A]] =
     Arbitrary(implicitly[Arbitrary[Vector[A]]].arbitrary.map(v => new ZipVector(v)))