marcinzh · May 30, 2025 11:51 · May 30, 2025
diff --git a/CatchFail_no_shadow.scala b/CatchFail_no_shadow.scala
@@ -0,0 +1,107 @@
+//> using scala "3.3.5"
+//> using dep "io.github.marcinzh::turbolift-core:0.112.0"
+//> using dep "io.github.marcinzh::turbolift-bindless:0.112.0"
+
+/************* HOW TO RUN ********************
+1. Ensure you have Java 11 or newer
+2. Install scala-cli
+3. Execute `scala-cli <link-to-this-gist>`
+**********************************************/
+
+import turbolift.{!!, Signature, Effect, Handler}
+import turbolift.effects.{Console, IO, Error, ErrorSignature}
+import turbolift.Extensions._
+import turbolift.bindless._
+
+
+trait ChoiceSignature extends Signature:
+  def fail(reason: String): Nothing !! ThisEffect
+  def choose: Boolean !! ThisEffect
+
+
+trait ChoiceEffect extends Effect[ChoiceSignature] with ChoiceSignature:
+  final override def fail(reason: String): Nothing !! ThisEffect = perform(_.fail(reason))
+  final override def choose: Boolean !! ThisEffect = perform(_.choose)
+
+
+extension (fx: ChoiceEffect)
+  def handler_NoThrowOnFail =
+    new fx.impl.Stateless[Identity, Vector, Any] with fx.impl.Sequential with ChoiceSignature:
+      override def onReturn(a: Unknown) = Vector(a).pure_!!
+      override def fail(reason: String): Nothing !! ThisEffect = Control.abort(Vector())
+      override def choose = Control.capture(k => k(false).zipWith(k(true))(_ ++ _))
+    .toHandler
+
+  // Takes an instance of `Error` effect as a dependency
+  def handler_ThrowOnFail(errorFx: Error[String]): Handler[Identity, Vector, fx.type, errorFx.type] =
+    new fx.impl.Stateless[Identity, Vector, errorFx.type] with fx.impl.Sequential with ChoiceSignature:
+      override def onReturn(a: Unknown) = Vector(a).pure_!!
+      override def fail(reason: String): Nothing !! ThisEffect = errorFx.raise(reason)
+      override def choose = Control.capture(k => k(false).zipWith(k(true))(_ ++ _))
+    .toHandler
+
+
+extension (fx: Error[String])
+  def hookLoggingToCatch[A, U <: Console & fx.type](comp: A !! U): A !! U =
+    // Mostly a copy & paste of the original handler for `Error` effect
+    new fx.impl.Stateless[Identity, [X] =>> Either[String, X], Console] with fx.impl.Sequential with ErrorSignature[String, String]:
+      override def onReturn(a: Unknown) = Right(a).pure_!!
+      override def raise(e: String) = Control.abort(Left(e))
+      override def raises(e: String) = Control.abort(Left(e))
+      override def toEither[A, U <: ThisEffect](comp: A !! U) = Control.delimit(comp)
+      override def catchAllEff[A, U <: ThisEffect](body: A !! U)(f: String => A !! U): A !! U =
+        toEither(
+          Console.println("[LOG] Entering catch scope...") &&!
+          body
+        ).flatMap:
+          case Right(a) => a.pure_!!
+          case Left(e) =>
+            Console.println(s"[LOG] Caught exception: $e") &&!
+            f(e)
+    .toHandler
+    .handle(comp)
+    .flatMap(fx.fromEither)
+
+
+/***************************************************************
+In Turbolift effects are not only types, but also values.
+See `Labelled Effects` at https://marcinzh.github.io/turbolift/advanced/labelled.html
+All code ABOVE is effect-instance-independent, taking them as parameters if required.
+All code BELOW depends on concrete effect instances.
+***************************************************************/
+case object MyError extends Error[String]
+case object MyChoice extends ChoiceEffect
+type MyError = MyError.type
+type MyChoice = MyChoice.type
+
+
+def failWhenBothTrue: (Boolean, Boolean) !! (MyChoice & Console) =
+  `do`:
+    val x = MyChoice.choose.!
+    val y = MyChoice.choose.!
+    if x && y then MyChoice.fail("x = y = True").!
+    Console.println(s"x=$x y=$y").!
+    (x, y)
+
+
+def catchFail: Option[(Boolean, Boolean)] !! (MyChoice & MyError & Console) =
+  MyError.catchAllEff(failWhenBothTrue.map(Some(_))): reason =>
+    Console.println(s"caught failure: $reason") &&!
+    None.pure_!!
+
+
+def program: Option[(Boolean, Boolean)] !! (MyChoice & MyError & Console) =
+  MyError.hookLoggingToCatch(catchFail)
+
+
+@main def main =
+  `do`:
+    Console.println("[NoThrowOnFail]").!
+    val r1 = program.handleWith(MyChoice.handler_NoThrowOnFail).handleWith(MyError.handler).!
+    Console.println(r1.toString).!
+    Console.println("").!
+    Console.println("[ThrowOnFail]").!
+    val r2 = program.handleWith(MyChoice.handler_ThrowOnFail(MyError)).handleWith(MyError.handler).!
+    Console.println(r2.toString).!
+  .handleWith(Console.handler)
+  .runIO