add tap and tapAsView and document how to use it for logging

core/src/main/scala/ox/channels/SourceOps.scala

@@ -28,6 +28,20 @@ trait SourceOps[+T] { outer: Source[T] =>
  override val delegate: JSource[Any] = outer.delegate.asInstanceOf[JSource[T]].collectAsView(t => f(t))
  }
 
+ /** Lazily-evaluated tap: creates a view of this source, where the results of [[receive]] will be applied to the given function `f` on the
+ * consumer's thread. Useful for logging and debugging values emitted from the source. For an eager, asynchronous version, see [[tap]].
+ *
+ * The same logic applies to receive clauses created using this source, which can be used in [[select]].
+ *
+ * @param f
+ * The consumer function.
+ * @return
+ * A source which is a view of this source, with the consumer function applied.
+ */
+ def tapAsView(f: T => Unit): Source[T] = new Source[T] {
+ override val delegate: JSource[Any] = outer.delegate.asInstanceOf[JSource[T]].collectAsView(t => { f(t); t })
+ }
+
  /** Lazily-evaluated filter: Creates a view of this source, where the results of [[receive]] will be filtered on the consumer's thread
  * using the given predicate `p`. For an eager, asynchronous version, see [[filter]].
  *
@@ -70,7 +84,7 @@ trait SourceOps[+T] { outer: Source[T] =>
  /** Applies the given mapping function `f` to each element received from this source, and sends the results to the returned channel.
  *
  * Errors from this channel are propagated to the returned channel. Any exceptions that occur when invoking `f` are propagated as errors
- * to the returned channel as wel.
+ * to the returned channel as well.
  *
  * Must be run within a scope, as a child fork is created, which receives from this source and sends the mapped values to the resulting
  * one.
@@ -101,6 +115,23 @@ trait SourceOps[+T] { outer: Source[T] =>
  }
  c2
 
+ /** Applies the given consumer function `f` to each element received from this source.
+ *
+ * Errors from this channel are propagated to the returned channel. Any exceptions that occur when invoking `f` are propagated as errors
+ * to the returned channel as well.
+ *
+ * Must be run within a scope, as a child fork is created, which receives from this source and sends the mapped values to the resulting
+ * one.
+ *
+ * Useful for logging and debugging values emitted from the source. For a lazily-evaluated version, see [[tapAsView]].
+ *
+ * @param f
+ * The consumer function.
+ * @return
+ * A source, which the elements from the input source are passed to.
+ */
+ def tap(f: T => Unit)(using Ox, StageCapacity): Source[T] = map(t => { f(t); t })
+
  /** Intersperses this source with provided element and forwards it to the returned channel.
  *
  * @param inject

core/src/test/scala/ox/channels/SourceOpsAsViewTest.scala

@@ -5,6 +5,7 @@ import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.matchers.should.Matchers
 import ox.*
 
+import java.util.concurrent.atomic.AtomicInteger
 import scala.jdk.CollectionConverters.*
 import scala.util.{Failure, Try}
 
@@ -111,6 +112,27 @@ class SourceOpsAsViewTest extends AnyFlatSpec with Matchers with Eventually {
  }
  }
 
+ it should "tap over a source as a view" in {
+ val c: Channel[Int] = Channel.rendezvous
+ val sum = new AtomicInteger()
+
+ supervised {
+ fork {
+ c.send(1)
+ c.send(2)
+ c.send(3)
+ c.done()
+ }
+
+ val s2 = c.tapAsView(v => sum.addAndGet(v).discard)
+ s2.receive() shouldBe 1
+ s2.receive() shouldBe 2
+ s2.receive() shouldBe 3
+ s2.receiveOrClosed() shouldBe ChannelClosed.Done
+ sum.get() shouldBe 6
+ }
+ }
+
  it should "propagate exceptions to the calling select" in {
  val c: Channel[Int] = Channel.rendezvous
 

core/src/test/scala/ox/channels/SourceOpsTest.scala

@@ -5,9 +5,11 @@ import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.matchers.should.Matchers
 import ox.*
 
+import java.util.concurrent.atomic.AtomicInteger
 import scala.concurrent.duration.DurationInt
 
 class SourceOpsTest extends AnyFlatSpec with Matchers with Eventually {
+
  it should "timeout" in {
  supervised {
  val c = Source.timeout(100.millis)
@@ -65,4 +67,12 @@ class SourceOpsTest extends AnyFlatSpec with Matchers with Eventually {
  s.toList shouldBe List("a", "b", "c", "d", "e", "f", "g", "h", "i")
  }
  }
+
+ it should "tap over a source" in {
+ supervised {
+ val sum = new AtomicInteger()
+ Source.fromValues(1, 2, 3).tap(v => sum.addAndGet(v).discard).toList shouldBe List(1, 2, 3)
+ sum.get() shouldBe 6
+ }
+ }
 }

doc/channels/transforming-sources.md

@@ -80,3 +80,23 @@ When dealing with Sources with chunks of bytes or Strings, you can leverage foll
 * `decodeStringUtf8` to decode a `Source[Chunk[Byte]]` into a `Source[String]`, without handling line breaks, just processing input bytes as UTF-8 characters, even if a multi-byte character is divided into two chunks.
 
 Such operations may be useful when dealing with I/O like files, `InputStream`, etc.. See [examples here](io.md).
+
+## Logging
+
+Ox does not have any integrations with logging libraries, but it provides a simple way to log elements flowing through channels
+using the `.tap` (eagerly evaluated) or `.tapAsView` (lazily evaluated) methods.
+
+```scala mdoc:compile-only
+import ox.supervised
+import ox.channels.Source
+
+supervised {
+ Source.fromValues(1, 2, 3)
+ .tap(n => println(s"Received: $n")) // prints as soon as the element is sent from the source
+ .toList
+
+ Source.fromValues(1, 2, 3)
+ .tapAsView(n => println(s"Received: $n")) // prints when the element is consumed by `toList`
+ .toList
+}
+```