add evalMapFilter (ocadotechnology#204)

scala-steward · Jan 24, 2023 · e04b8f2 · e04b8f2
1 parent 9e5a1ed
commit e04b8f2
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diff --git a/kernel/src/main/scala/com/ocadotechnology/pass4s/kernel/Consumer.scala b/kernel/src/main/scala/com/ocadotechnology/pass4s/kernel/Consumer.scala
@@ -257,6 +257,13 @@ object Consumer extends ConsumerInstances {
     def mapM[B](f: A => F[B])(implicit F: FlatMap[F]): Consumer[F, B] =
       handler => self.consume(f >=> handler)
 
+    /** Allows to filter certain messages and execute an effect while doing it.
+      *
+      * For filtering without an effect use [[functorFilter]] instance.
+      */
+    def evalMapFilter[B](f: A => F[Option[B]])(implicit F: Monad[F]): Consumer[F, B] =
+      Consumer.fromFunction[F, B](handler => self.consume(f(_).flatMap(_.fold(Applicative[F].unit)(handler))))
+
     /** Similar to [[mapM()]], but discards the result of the tapped effect.
       */
     def contraTapM(f: A => F[Unit])(implicit F: FlatMap[F]): Consumer[F, A] =

diff --git a/kernel/src/test/scala/com/ocadotechnology/pass4s/kernel/ConsumerOpsTests.scala b/kernel/src/test/scala/com/ocadotechnology/pass4s/kernel/ConsumerOpsTests.scala
@@ -44,6 +44,25 @@ object ConsumerOpsTests extends SimpleMutableIOSuite with Checkers {
     )
   }
 
+  test("Consumer#evalMapFilter") {
+    for {
+      consumed     <- Sender.testing[IO, Int]
+      ignored      <- Sender.testing[IO, Int]
+      _            <- Consumer
+                        .many[IO, Int](0 until 6: _*)
+                        .evalMapFilter {
+                          case i if i % 2 === 0 => IO.pure(Some(i))
+                          case i                => ignored.sendOne(i).as(None)
+                        }
+                        .forward(consumed)
+      consumedSent <- consumed.sent
+      ignoredSent  <- ignored.sent
+    } yield assert.all(
+      consumedSent == List(0, 2, 4),
+      ignoredSent == List(1, 3, 5)
+    )
+  }
+
   test("Consumer#surroundEachWith") {
     for {
       sender <- Sender.testing[IO, Int]