Merge pull request #20 from typelevel/topic/foldmap

Add foldMap and Monoid[Map[K, V]] and fix Monoid[Option[A]]

.gitignore

@@ -7,3 +7,4 @@ target
 .vscode
 project/metals.sbt
 project/project
+.scala-build

build.sbt

@@ -29,5 +29,7 @@ lazy val root = tlCrossRootProject
 lazy val core = crossProject(JVMPlatform, JSPlatform)
   .settings(
     name := "spotted-leopards",
-    libraryDependencies += "org.scalameta" %%% "munit-scalacheck" % "0.7.29"
+    libraryDependencies += "org.scalameta" %%% "munit-scalacheck" % "0.7.29",
+    Compile / console / scalacOptions := (Compile / console / scalacOptions).value
+      .filterNot(_.startsWith("-Wunused"))
   )

core/shared/src/main/scala/leopards/Monoid.scala

@@ -18,3 +18,11 @@ package leopards
 
 trait Monoid[A] extends Semigroup[A]:
   def empty: A
+
+  extension (as: IterableOnce[A])
+    def combineAll: A =
+      as.foldMap(identity)(using this)
+
+extension [A](as: IterableOnce[A])
+  def foldMap[B](f: A => B)(using m: Monoid[B]): B =
+    as.iterator.foldLeft(m.empty)((acc, a) => acc |+| f(a))

core/shared/src/main/scala/leopards/Semigroup.scala

@@ -24,3 +24,4 @@ object Semigroup:
   export leopards.intMonoid
   export leopards.stdListMonoid
   export leopards.stdOptionMonoid
+  export leopards.mapMergeMonoid

core/shared/src/main/scala/leopards/instances/map.scala

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2019 Typelevel
+ *
+ * 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 leopards
+
+given mapMergeMonoid[A, B: Semigroup]: Monoid[Map[A, B]] with
+  val empty = Map.empty
+  def combine(x: Map[A, B], y: Map[A, B]) =
+    y.foldLeft(x):
+      case (acc, (k, v)) =>
+        acc.updatedWith(k)(_ |+| Some(v))

core/shared/src/main/scala/leopards/instances/option.scala

@@ -27,4 +27,10 @@ given stdOptionInstances: Monad[Option] with Traverse[Option] with
 
 given stdOptionMonoid[A: Semigroup]: Monoid[Option[A]] with
   def empty = None
-  def combine(x: Option[A], y: Option[A]) = x.flatMap(xx => y.map(yy => xx |+| yy))
+  def combine(x: Option[A], y: Option[A]) =
+    x match
+      case None => y
+      case Some(xx) =>
+        y match
+          case None     => x
+          case Some(yy) => Some(xx |+| yy)