Add TraverseFilter instance for Map to alleycats

alleycats-core/src/main/scala/alleycats/std/all.scala

@@ -15,3 +15,4 @@ import export._
     with LegacyTryInstances
     with LegacyIterableInstances
     with MapInstances
+    with MapInstancesBinCompat0

alleycats-core/src/main/scala/alleycats/std/map.scala

@@ -3,7 +3,7 @@ package std
 
 import cats._
 
-object map extends MapInstances
+object map extends MapInstances with MapInstancesBinCompat0
 
 trait MapInstances {
 
@@ -59,3 +59,21 @@ trait MapInstances {
         collectFirst(fa)(Function.unlift(f))
     }
 }
+
+trait MapInstancesBinCompat0 extends MapInstances {
+  implicit def mapTraverseFilter[K]: TraverseFilter[Map[K, ?]] =
+    new TraverseFilter[Map[K, ?]] {
+      def traverse: Traverse[Map[K, ?]] = alleycatsStdInstancesForMap
+
+      def traverseFilter[G[_], A, B](fa: Map[K, A])(f: A => G[Option[B]])(implicit G: Applicative[G]): G[Map[K, B]] = {
+        val gba: Eval[G[Map[K, B]]] = Always(G.pure(Map.empty))
+        Foldable
+          .iterateRight(fa, gba) { (kv, lbuf) =>
+            G.map2Eval(f(kv._2), lbuf)({ (ob, buf) =>
+              ob.fold(buf)(b => buf + (kv._1 -> b))
+            })
+          }
+          .value
+      }
+    }
+}

alleycats-tests/src/test/scala/alleycats/tests/MapSuite.scala

@@ -1,8 +1,12 @@
 package alleycats.tests
 
-import cats.laws.discipline.SerializableTests
+import cats.laws.discipline.arbitrary._
+import cats.laws.discipline.{SerializableTests, TraverseFilterTests}
 import cats.Traverse
+import alleycats.std.all._
 
 class MapSuite extends AlleycatsSuite {
   checkAll("Traverse[Map[Int, ?]]", SerializableTests.serializable(Traverse[Map[Int, ?]]))
+
+  checkAll("TraverseFilter[Map[Int, ?]]", TraverseFilterTests[Map[Int, ?]].traverseFilter[Int, Int, Int])
 }