reader contravariant on input (#2922)

typelevel · Jun 28, 2019 · 8387863 · 8387863
1 parent 9c2371a
commit 8387863
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diff --git a/core/src/main/scala/cats/data/Kleisli.scala b/core/src/main/scala/cats/data/Kleisli.scala
@@ -114,7 +114,7 @@ final case class Kleisli[F[_], -A, B](run: A => F[B]) { self =>
   def tapWithF[C, AA <: A](f: (AA, B) => F[C])(implicit F: FlatMap[F]): Kleisli[F, AA, C] =
     Kleisli(a => F.flatMap(run(a))(b => f(a, b)))
 
-  def toReader[AA <: A]: Reader[AA, F[B]] = Kleisli[Id, AA, F[B]](run)
+  def toReader: Reader[A, F[B]] = Kleisli[Id, A, F[B]](run)
 
   def apply(a: A): F[B] = run(a)
 }

diff --git a/core/src/main/scala/cats/data/package.scala b/core/src/main/scala/cats/data/package.scala
@@ -30,10 +30,10 @@ package object data {
   type NonEmptyChain[+A] = NonEmptyChainImpl.Type[A]
   val NonEmptyChain = NonEmptyChainImpl
 
-  type ReaderT[F[_], A, B] = Kleisli[F, A, B]
+  type ReaderT[F[_], -A, B] = Kleisli[F, A, B]
   val ReaderT = Kleisli
 
-  type Reader[A, B] = ReaderT[Id, A, B]
+  type Reader[-A, B] = ReaderT[Id, A, B]
 
   object Reader {
     def apply[A, B](f: A => B): Reader[A, B] = ReaderT[Id, A, B](f)