Merge pull request #2 from tschuchortdev/fix_classcast

Fix ClassCastException in TraverseK

Author: tschuchortdev

build.sbt

@@ -17,11 +17,11 @@ ThisBuild / scalacOptions ++= Seq(
   "-language:experimental.macros",
   "-language:implicitConversions",
   "-language:higherKinds",
-  "-language:namedTypeArguments",
-  "-language:saferExceptions",
+  //"-language:namedTypeArguments",
+  //"-language:saferExceptions",
   "-language:dynamics",
-  "-language:numericLiterals",
-  // "-Ykind-projector:underscores",
+  //"-language:numericLiterals",
+  "-Xkind-projector:underscores",
   "-unchecked",
   // "-Ysafe-init", // Note: causes warnings when used with Shapeless 3 recursive derivation
   // "-Yexplicit-nulls", // Make reference types non-nullable: String != String|Null
@@ -99,6 +99,7 @@ lazy val root = (project in file("."))
       "org.typelevel" %% "mouse" % "1.3.1", // helper functions
       "org.typelevel" %% "kittens" % "3.3.0", // type class derivation
       "org.typelevel" %% "cats-collections-core" % "0.9.8",
+      "org.typelevel" %% "cats-effect" % "3.5.7"
     ).map(_ % Test),
 
     Test / parallelExecution := true

src/main/scala/BasicTypeclasses.scala

@@ -293,10 +293,13 @@ object TraverseK {
   given adtTraverseK[D[_[_]]](using pInst: K11.Instances[TraverseK, D]): TraverseK[D] with {
     extension [F[_]](df: D[F])
       override def traverseK[G[+_], H[_]](f: [A] => F[A] => G[H[A]])(using Applicative[G]): G[D[H]] =
-        pInst.traverse(df)(Applicative[G].map.asInstanceOf[shapeless3.deriving.MapF[G]])(
-          Applicative[G].pure.asInstanceOf[shapeless3.deriving.Pure[G]]
+        pInst.traverse(df)(
+          ([A, B] => (ga: G[A], ab: A => B) => Applicative[G].map(ga)(ab)).asInstanceOf[shapeless3.deriving.MapF[G]]
+        )(
+          [A] => (a: A) => Applicative[G].pure(a)
+        )(
+          [A, B] => (gg: G[A => B], ga: G[A]) => Applicative[G].ap(gg)(ga)
         )(
-          Applicative[G].ap.asInstanceOf[shapeless3.deriving.Ap[G]])(
           [t[_[_]]] => (fieldTraversableK: TraverseK[t], field: t[F]) => fieldTraversableK.traverseK(field)(f)
         )
   }

src/test/scala/TypeclassesTest.scala

@@ -1,7 +1,12 @@
 package com.tschuchort.hkd
 
-import cats.Show
+import cats.{Applicative, Id, Show}
 import cats.data.Const
+import cats.data.Writer
+import cats.effect.IO
+import com.tschuchort.hkd.internal.`.`
+import cats.syntax.all
+import cats.effect.unsafe.implicits.global
 
 class TypeclassesTest extends munit.FunSuite {
   sealed trait FooHK[F[_]]
@@ -109,4 +114,13 @@ class TypeclassesTest extends munit.FunSuite {
       case _ => throw AssertionError(s"Expected Contra21HK, was: $mapped")
   }
 
+  test("TraverseK sequences effects") {
+    case class BarHK[F[_]](a: F[Int], b: F[Int], c: F[Int])
+    var res = ""
+    // Have to use IO here because Writer won't type-check for some reason
+    val bar = BarHK[IO `.` Option](IO { res += "1"; Some(1) }, IO { res += "2"; Some(2) }, IO { res += "3"; Some(3) })
+    val bar2 = TraverseK[BarHK].sequenceK(bar).unsafeRunSync()
+    assertEquals(res, "123")
+    assertEquals(bar2, BarHK[Option](Some(1), Some(2), Some(3)))
+  }
 }