Implement local for Reader

typelevel · Jun 27, 2019 · 98358ac · 98358ac
1 parent 162ee0f
commit 98358ac
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diff --git a/core/src/main/scala/cats/data/package.scala b/core/src/main/scala/cats/data/package.scala
@@ -34,6 +34,8 @@ package object data {
 
   object Reader {
     def apply[A, B](f: A => B): Reader[A, B] = ReaderT[Id, A, B](f)
+
+    def local[A, R](f: R => R)(fa: Reader[R, A]): Reader[R, A] = Kleisli.local(f)(fa)
   }
 
   type Writer[L, V] = WriterT[Id, L, V]

diff --git a/tests/src/test/scala/cats/tests/KleisliSuite.scala b/tests/src/test/scala/cats/tests/KleisliSuite.scala
@@ -260,6 +260,20 @@ class KleisliSuite extends CatsSuite {
     kconfig1.run(config) should ===(kconfig2.run(config))
   }
 
+  test("local for Reader") {
+    val rint1 = Reader { (x: Int) =>
+      x.toDouble
+    }
+    val rint1local = Reader.local((i: Int) => i * 2)(rint1)
+    val rint2 = Reader { (i: Int) =>
+      (i * 2).toDouble
+    }
+
+    val config = 10
+    rint1local.run(config) should ===(rint2.run(config))
+
+  }
+
   test("flatMap is stack safe on repeated left binds when F is") {
     val unit = Kleisli.pure[Eval, Unit, Unit](())
     val count = if (Platform.isJvm) 10000 else 100