max and min methods for NonEmptyList

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

@@ -383,6 +383,12 @@ public class NonEmptyList<out A>(
       map(head, b.head, c.head, d.head, e.head, f.head, g.head, h.head, i.head, j.head),
       tail.zip(b.tail, c.tail, d.tail, e.tail, f.tail, g.tail, h.tail, i.tail, j.tail, map)
     )
+
+  public inline fun <B : Comparable<B>> minBy(selector: (A) -> B): A =
+    minByOrNull(selector) ?: head
+
+  public inline fun <B : Comparable<B>> maxBy(selector: (A) -> B): A =
+    maxByOrNull(selector) ?: head
 }
 
 public fun <A> nonEmptyListOf(head: A, vararg t: A): NonEmptyList<A> =
@@ -397,6 +403,12 @@ public operator fun <A : Comparable<A>> NonEmptyList<A>.compareTo(other: NonEmpt
 public fun <A> NonEmptyList<NonEmptyList<A>>.flatten(): NonEmptyList<A> =
   this.flatMap(::identity)
 
+public inline fun <T : Comparable<T>> NonEmptyList<T>.min(): T =
+  minOrNull() ?: head
+
+public inline fun <T : Comparable<T>> NonEmptyList<T>.max(): T =
+  maxOrNull() ?: head
+
 public fun <A, B> NonEmptyList<Pair<A, B>>.unzip(): Pair<NonEmptyList<A>, NonEmptyList<B>> =
   this.unzip(::identity)
 

arrow-libs/core/arrow-core/src/commonTest/kotlin/arrow/core/NonEmptyListTest.kt

@@ -4,7 +4,6 @@ import arrow.core.test.UnitSpec
 import arrow.core.test.laws.SemigroupLaws
 import arrow.typeclasses.Semigroup
 import io.kotest.property.Arb
-import io.kotest.property.checkAll
 import io.kotest.matchers.shouldBe
 import io.kotest.property.arbitrary.boolean
 import io.kotest.property.arbitrary.int
@@ -268,5 +267,46 @@ class NonEmptyListTest : UnitSpec() {
         result shouldBe expected
       }
     }
+
+    "max element" {
+      checkAll(
+        Arb.nonEmptyList(Arb.int())
+      ) { a ->
+        val result = a.max()
+        val expected = a.maxOrNull()
+        result shouldBe expected
+      }
+    }
+
+    "maxBy element" {
+      checkAll(
+        Arb.nonEmptyList(Arb.int())
+      ) { a ->
+        val result = a.maxBy(::identity)
+        val expected = a.maxByOrNull(::identity)
+        result shouldBe expected
+      }
+    }
+
+    "min element" {
+      checkAll(
+        Arb.nonEmptyList(Arb.int())
+      ) { a ->
+        val result = a.min()
+        val expected = a.minOrNull()
+        result shouldBe expected
+      }
+    }
+
+
+    "minBy element" {
+      checkAll(
+        Arb.nonEmptyList(Arb.int())
+      ) { a ->
+        val result = a.minBy(::identity)
+        val expected = a.minByOrNull(::identity)
+        result shouldBe expected
+      }
+    }
   }
 }