Introduce NonEmptyCollection

arrow-libs/core/arrow-core/api/arrow-core.api

@@ -776,34 +776,74 @@ public final class arrow/core/Memoization {
 	public static final fun memoize (Lkotlin/jvm/functions/Function5;)Lkotlin/jvm/functions/Function5;
 }
 
-public final class arrow/core/NonEmptyList : kotlin/collections/AbstractList {
+public abstract interface class arrow/core/NonEmptyCollection : java/util/Collection, kotlin/jvm/internal/markers/KMappedMarker {
+	public abstract fun distinct ()Larrow/core/NonEmptyList;
+	public abstract fun distinctBy (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public abstract fun firstOrNull ()Ljava/lang/Object;
+	public abstract fun flatMap (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public abstract fun getHead ()Ljava/lang/Object;
+	public abstract fun isEmpty ()Z
+	public abstract fun lastOrNull ()Ljava/lang/Object;
+	public abstract fun map (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public abstract fun mapIndexed (Lkotlin/jvm/functions/Function2;)Larrow/core/NonEmptyList;
+	public abstract fun plus (Ljava/lang/Iterable;)Larrow/core/NonEmptyCollection;
+	public abstract fun plus (Ljava/lang/Object;)Larrow/core/NonEmptyCollection;
+	public abstract fun toNonEmptyList ()Larrow/core/NonEmptyList;
+	public abstract fun toNonEmptySet-5sCjGKo ()Ljava/util/Set;
+	public abstract fun zip (Larrow/core/NonEmptyCollection;)Larrow/core/NonEmptyCollection;
+}
+
+public final class arrow/core/NonEmptyCollection$DefaultImpls {
+	public static fun distinct (Larrow/core/NonEmptyCollection;)Larrow/core/NonEmptyList;
+	public static fun distinctBy (Larrow/core/NonEmptyCollection;Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public static fun firstOrNull (Larrow/core/NonEmptyCollection;)Ljava/lang/Object;
+	public static fun flatMap (Larrow/core/NonEmptyCollection;Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public static fun isEmpty (Larrow/core/NonEmptyCollection;)Z
+	public static fun map (Larrow/core/NonEmptyCollection;Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public static fun mapIndexed (Larrow/core/NonEmptyCollection;Lkotlin/jvm/functions/Function2;)Larrow/core/NonEmptyList;
+	public static fun toNonEmptyList (Larrow/core/NonEmptyCollection;)Larrow/core/NonEmptyList;
+	public static fun toNonEmptySet-5sCjGKo (Larrow/core/NonEmptyCollection;)Ljava/util/Set;
+	public static fun zip (Larrow/core/NonEmptyCollection;Larrow/core/NonEmptyCollection;)Larrow/core/NonEmptyCollection;
+}
+
+public final class arrow/core/NonEmptyList : kotlin/collections/AbstractList, arrow/core/NonEmptyCollection {
 	public static final field Companion Larrow/core/NonEmptyList$Companion;
 	public fun <init> (Ljava/lang/Object;Ljava/util/List;)V
 	public synthetic fun <init> (Ljava/util/List;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun align (Larrow/core/NonEmptyList;)Larrow/core/NonEmptyList;
 	public final fun coflatMap (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public fun distinct ()Larrow/core/NonEmptyList;
+	public fun distinctBy (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
 	public fun equals (Ljava/lang/Object;)Z
 	public final fun extract ()Ljava/lang/Object;
-	public final fun flatMap (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public fun firstOrNull ()Ljava/lang/Object;
+	public fun flatMap (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
 	public final fun foldLeft (Ljava/lang/Object;Lkotlin/jvm/functions/Function2;)Ljava/lang/Object;
 	public static final fun fromList (Ljava/util/List;)Larrow/core/Option;
 	public static final fun fromListUnsafe (Ljava/util/List;)Larrow/core/NonEmptyList;
 	public fun get (I)Ljava/lang/Object;
 	public final fun getAll ()Ljava/util/List;
-	public final fun getHead ()Ljava/lang/Object;
+	public fun getHead ()Ljava/lang/Object;
 	public fun getSize ()I
 	public final fun getTail ()Ljava/util/List;
 	public fun hashCode ()I
 	public fun isEmpty ()Z
-	public final fun map (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public fun lastOrNull ()Ljava/lang/Object;
+	public fun map (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public fun mapIndexed (Lkotlin/jvm/functions/Function2;)Larrow/core/NonEmptyList;
 	public final fun padZip (Larrow/core/NonEmptyList;)Larrow/core/NonEmptyList;
 	public final fun padZip (Larrow/core/NonEmptyList;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function2;)Larrow/core/NonEmptyList;
 	public final fun plus (Larrow/core/NonEmptyList;)Larrow/core/NonEmptyList;
-	public final fun plus (Ljava/lang/Object;)Larrow/core/NonEmptyList;
-	public final fun plus (Ljava/util/List;)Larrow/core/NonEmptyList;
+	public synthetic fun plus (Ljava/lang/Iterable;)Larrow/core/NonEmptyCollection;
+	public fun plus (Ljava/lang/Iterable;)Larrow/core/NonEmptyList;
+	public synthetic fun plus (Ljava/lang/Object;)Larrow/core/NonEmptyCollection;
+	public fun plus (Ljava/lang/Object;)Larrow/core/NonEmptyList;
 	public final fun salign (Larrow/typeclasses/Semigroup;Larrow/core/NonEmptyList;)Larrow/core/NonEmptyList;
 	public final fun toList ()Ljava/util/List;
+	public fun toNonEmptyList ()Larrow/core/NonEmptyList;
+	public fun toNonEmptySet-5sCjGKo ()Ljava/util/Set;
 	public fun toString ()Ljava/lang/String;
+	public fun zip (Larrow/core/NonEmptyCollection;)Larrow/core/NonEmptyCollection;
 	public final fun zip (Larrow/core/NonEmptyList;)Larrow/core/NonEmptyList;
 	public final fun zip (Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Lkotlin/jvm/functions/Function10;)Larrow/core/NonEmptyList;
 	public final fun zip (Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Larrow/core/NonEmptyList;Lkotlin/jvm/functions/Function9;)Larrow/core/NonEmptyList;
@@ -851,7 +891,7 @@ public final class arrow/core/NonEmptyListKt {
 	public static final fun unzip (Larrow/core/NonEmptyList;Lkotlin/jvm/functions/Function1;)Lkotlin/Pair;
 }
 
-public final class arrow/core/NonEmptySet : java/util/Set, kotlin/jvm/internal/markers/KMappedMarker {
+public final class arrow/core/NonEmptySet : arrow/core/NonEmptyCollection, java/util/Set, kotlin/jvm/internal/markers/KMappedMarker {
 	public fun add (Ljava/lang/Object;)Z
 	public fun addAll (Ljava/util/Collection;)Z
 	public static final synthetic fun box-impl (Ljava/util/Set;)Larrow/core/NonEmptySet;
@@ -861,9 +901,19 @@ public final class arrow/core/NonEmptySet : java/util/Set, kotlin/jvm/internal/m
 	public static fun contains-impl (Ljava/util/Set;Ljava/lang/Object;)Z
 	public fun containsAll (Ljava/util/Collection;)Z
 	public static fun containsAll-impl (Ljava/util/Set;Ljava/util/Collection;)Z
+	public fun distinct ()Larrow/core/NonEmptyList;
+	public static fun distinct-impl (Ljava/util/Set;)Larrow/core/NonEmptyList;
+	public fun distinctBy (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public static fun distinctBy-impl (Ljava/util/Set;Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
 	public fun equals (Ljava/lang/Object;)Z
 	public static fun equals-impl (Ljava/util/Set;Ljava/lang/Object;)Z
 	public static final fun equals-impl0 (Ljava/util/Set;Ljava/util/Set;)Z
+	public fun firstOrNull ()Ljava/lang/Object;
+	public static fun firstOrNull-impl (Ljava/util/Set;)Ljava/lang/Object;
+	public fun flatMap (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public static fun flatMap-impl (Ljava/util/Set;Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public fun getHead ()Ljava/lang/Object;
+	public static fun getHead-impl (Ljava/util/Set;)Ljava/lang/Object;
 	public fun getSize ()I
 	public static fun getSize-impl (Ljava/util/Set;)I
 	public fun hashCode ()I
@@ -872,18 +922,33 @@ public final class arrow/core/NonEmptySet : java/util/Set, kotlin/jvm/internal/m
 	public static fun isEmpty-impl (Ljava/util/Set;)Z
 	public fun iterator ()Ljava/util/Iterator;
 	public static fun iterator-impl (Ljava/util/Set;)Ljava/util/Iterator;
-	public static final fun map-J9TPrxk (Ljava/util/Set;Lkotlin/jvm/functions/Function1;)Ljava/util/Set;
-	public static final fun plus-J9TPrxk (Ljava/util/Set;Ljava/lang/Object;)Ljava/util/Set;
-	public static final fun plus-J9TPrxk (Ljava/util/Set;Ljava/util/Set;)Ljava/util/Set;
+	public fun lastOrNull ()Ljava/lang/Object;
+	public static fun lastOrNull-impl (Ljava/util/Set;)Ljava/lang/Object;
+	public fun map (Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public static fun map-impl (Ljava/util/Set;Lkotlin/jvm/functions/Function1;)Larrow/core/NonEmptyList;
+	public fun mapIndexed (Lkotlin/jvm/functions/Function2;)Larrow/core/NonEmptyList;
+	public static fun mapIndexed-impl (Ljava/util/Set;Lkotlin/jvm/functions/Function2;)Larrow/core/NonEmptyList;
+	public synthetic fun plus (Ljava/lang/Iterable;)Larrow/core/NonEmptyCollection;
+	public synthetic fun plus (Ljava/lang/Object;)Larrow/core/NonEmptyCollection;
+	public fun plus-J9TPrxk (Ljava/lang/Iterable;)Ljava/util/Set;
+	public fun plus-J9TPrxk (Ljava/lang/Object;)Ljava/util/Set;
+	public static fun plus-J9TPrxk (Ljava/util/Set;Ljava/lang/Iterable;)Ljava/util/Set;
+	public static fun plus-J9TPrxk (Ljava/util/Set;Ljava/lang/Object;)Ljava/util/Set;
 	public fun remove (Ljava/lang/Object;)Z
 	public fun removeAll (Ljava/util/Collection;)Z
 	public fun retainAll (Ljava/util/Collection;)Z
 	public synthetic fun size ()I
 	public fun toArray ()[Ljava/lang/Object;
 	public fun toArray ([Ljava/lang/Object;)[Ljava/lang/Object;
+	public fun toNonEmptyList ()Larrow/core/NonEmptyList;
+	public static fun toNonEmptyList-impl (Ljava/util/Set;)Larrow/core/NonEmptyList;
+	public fun toNonEmptySet-5sCjGKo ()Ljava/util/Set;
+	public static fun toNonEmptySet-5sCjGKo (Ljava/util/Set;)Ljava/util/Set;
 	public fun toString ()Ljava/lang/String;
 	public static fun toString-impl (Ljava/util/Set;)Ljava/lang/String;
 	public final synthetic fun unbox-impl ()Ljava/util/Set;
+	public fun zip (Larrow/core/NonEmptyCollection;)Larrow/core/NonEmptyCollection;
+	public static fun zip-impl (Ljava/util/Set;Larrow/core/NonEmptyCollection;)Larrow/core/NonEmptyCollection;
 }
 
 public final class arrow/core/NonEmptySetKt {

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/NonEmptyCollection.kt

@@ -0,0 +1,42 @@
+package arrow.core
+
+/**
+ * Common interface for collections that always have
+ * at least one element (available from [head]).
+ */
+public interface NonEmptyCollection<out A> : Collection<A> {
+  override fun isEmpty(): Boolean = false
+  public val head: A
+
+  public operator fun plus(element: @UnsafeVariance A): NonEmptyCollection<A>
+  public operator fun plus(elements: Iterable<@UnsafeVariance A>): NonEmptyCollection<A>
+
+  public fun toNonEmptySet(): NonEmptySet<A> = toNonEmptySetOrNull()!!
+  public fun toNonEmptyList(): NonEmptyList<A> = toNonEmptyListOrNull()!!
+
+  // These functions take precedence over the extensions in [Collection].
+  // This way non-emptiness is tracked by the type system.
+
+  public fun firstOrNull(): A = head
+  public fun lastOrNull(): A
+
+  public fun distinct(): NonEmptyList<A> =
+    delegate { it.distinct() }
+  public fun <K> distinctBy(selector: (A) -> K): NonEmptyList<A> =
+    delegate { it.distinctBy(selector) }
+  public fun <B> flatMap(transform: (A) -> NonEmptyCollection<B>): NonEmptyList<B> =
+    delegate { it.flatMap(transform) }
+  public fun <B> map(transform: (A) -> B): NonEmptyList<B> =
+    delegate { it.map(transform) }
+  public fun <B> mapIndexed(transform: (index:Int, A) -> B): NonEmptyList<B> =
+    delegate { it.mapIndexed(transform) }
+  public fun <B> zip(other: NonEmptyCollection<B>): NonEmptyCollection<Pair<A, B>> =
+    delegate { it.zip(other) }
+
+  /**
+   * Convenience method which delegates the implementation to [Collection],
+   * and wraps the resulting [List] as a non-empty one.
+   */
+  private inline fun <R> delegate(crossinline f: (Collection<A>) -> List<R>): NonEmptyList<R> =
+    f(this as Collection<A>).toNonEmptyListOrNull()!!
+}

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/NonEmptyList.kt

@@ -153,9 +153,9 @@ public typealias Nel<A> = NonEmptyList<A>
  *
  */
 public class NonEmptyList<out A>(
-  public val head: A,
+  public override val head: A,
   public val tail: List<A>
-) : AbstractList<A>() {
+) : AbstractList<A>(), NonEmptyCollection<A> {
 
   private constructor(list: List<A>) : this(list[0], list.drop(1))
 
@@ -174,20 +174,26 @@ public class NonEmptyList<out A>(
 
   public fun toList(): List<A> = listOf(head) + tail
 
-  public inline fun <B> map(f: (A) -> B): NonEmptyList<B> =
-    NonEmptyList(f(head), tail.map(f))
+  override fun lastOrNull(): A = when {
+    tail.isNotEmpty() -> tail.last()
+    else -> head
+  }
+
+  @Suppress("OVERRIDE_BY_INLINE")
+  public override inline fun <B> map(transform: (A) -> B): NonEmptyList<B> =
+    NonEmptyList(transform(head), tail.map(transform))
 
-  public inline fun <B> flatMap(f: (A) -> NonEmptyList<B>): NonEmptyList<B> =
-    f(head) + tail.flatMap { f(it).all }
+  override fun <B> flatMap(transform: (A) -> NonEmptyCollection<B>): NonEmptyList<B> =
+    transform(head).toNonEmptyList() + tail.flatMap(transform)
 
   public operator fun plus(l: NonEmptyList<@UnsafeVariance A>): NonEmptyList<A> =
-    NonEmptyList(all + l.all)
+    this + l.all
 
-  public operator fun plus(l: List<@UnsafeVariance A>): NonEmptyList<A> =
-    NonEmptyList(all + l)
+  public override operator fun plus(elements: Iterable<@UnsafeVariance A>): NonEmptyList<A> =
+    NonEmptyList(all + elements)
 
-  public operator fun plus(a: @UnsafeVariance A): NonEmptyList<A> =
-    NonEmptyList(all + a)
+  public override operator fun plus(element: @UnsafeVariance A): NonEmptyList<A> =
+    NonEmptyList(all + element)
 
   public inline fun <B> foldLeft(b: B, f: (B, A) -> B): B =
     this.tail.fold(f(b, this.head), f)

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/NonEmptySet.kt

@@ -5,21 +5,22 @@ import kotlin.jvm.JvmInline
 @JvmInline
 public value class NonEmptySet<out A> private constructor(
   private val elements: Set<A>
-) : Set<A> by elements {
+) : Set<A> by elements, NonEmptyCollection<A> {
 
   public constructor(first: A, rest: Set<A>) : this(setOf(first) + rest)
 
-  public operator fun plus(set: Set<@UnsafeVariance A>): NonEmptySet<A> =
-    NonEmptySet(elements + set)
+  public override operator fun plus(elements: Iterable<@UnsafeVariance A>): NonEmptySet<A> =
+    NonEmptySet(this.elements + elements)
 
-  public operator fun plus(element: @UnsafeVariance A): NonEmptySet<A> =
-    NonEmptySet(elements + element)
-
-  public fun <R> map(transform: (@UnsafeVariance A) -> R): NonEmptySet<R> =
-    NonEmptySet(elements.mapTo(mutableSetOf(), transform))
+  public override operator fun plus(element: @UnsafeVariance A): NonEmptySet<A> =
+    NonEmptySet(this.elements + element)
 
   override fun isEmpty(): Boolean = false
 
+  override val head: A get() = elements.first()
+
+  override fun lastOrNull(): A = elements.last()
+
   override fun toString(): String = "NonEmptySet(${this.joinToString()})"
 
   @Suppress("RESERVED_MEMBER_INSIDE_VALUE_CLASS")

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/raise/Builders.kt

@@ -105,7 +105,7 @@ public class ResultRaise(private val raise: Raise<Throwable>) : Raise<Throwable>
   @RaiseDSL
   @JvmName("bindAllResult")
   public fun <A> NonEmptySet<Result<A>>.bindAll(): NonEmptySet<A> =
-    map { it.bind() }
+    map { it.bind() }.toNonEmptySet()
 
   @RaiseDSL
   public inline fun <A> recover(
@@ -138,7 +138,7 @@ public class OptionRaise(private val raise: Raise<None>) : Raise<None> by raise
   @RaiseDSL
   @JvmName("bindAllOption")
   public fun <A> NonEmptySet<Option<A>>.bindAll(): NonEmptySet<A> =
-    map { it.bind() }
+    map { it.bind() }.toNonEmptySet()
 
   @RaiseDSL
   public fun ensure(value: Boolean): Unit = ensure(value) { None }
@@ -181,7 +181,7 @@ public class IorRaise<Error> @PublishedApi internal constructor(
   @RaiseDSL
   @JvmName("bindAllIor")
   public fun <A> NonEmptySet<Ior<Error, A>>.bindAll(): NonEmptySet<A> =
-    map { it.bind() }
+    map { it.bind() }.toNonEmptySet()
 
   @RaiseDSL
   public fun <A> Ior<Error, A>.bind(): A =

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/raise/Raise.kt

@@ -316,7 +316,7 @@ public interface Raise<in Error> {
 
   @RaiseDSL
   public fun <A> NonEmptySet<Either<Error, A>>.bindAll(): NonEmptySet<A> =
-    map { it.bind() }
+    map { it.bind() }.toNonEmptySet()
 }
 
 /**