feat: add semigroupk syntaxes

core/src/main/scala/kuram/syntax/all.scala

@@ -35,4 +35,5 @@ private[syntax] trait AllSyntax
     with MonoidSyntax
     with SemigroupSyntax
     with SemigroupalSyntax
+    with SemigroupKSyntax
     with AlternativeSyntax

core/src/main/scala/kuram/syntax/package.scala

@@ -35,5 +35,6 @@ package object syntax {
   object applicative extends ApplicativeSyntax
   object flatmap extends FlatMapSyntax
   object monad extends MonadSyntax
+  object semigroupk extends SemigroupKSyntax
   object alternative extends AlternativeSyntax
 }

core/src/main/scala/kuram/syntax/semigroupk.scala

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2024 lamdalib
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package kuram
+package syntax
+
+import kuram.kinds.SemigroupK
+
+private[syntax] trait SemigroupKSyntax {
+  extension [F[_], A](a: F[A])(using SemigroupK[F]) {
+    final def combineK(b: F[A]): F[A] = {
+      SemigroupK[F].combineK(a, b)
+    }
+
+    final def <+>(b: F[A]): F[A] = {
+      combineK(b)
+    }
+  }
+}