Merge pull request #5 from armanbilge/local

Add Local via IOLocal
armanbilge · Feb 17, 2022 · d275a9e · d275a9e
2 parents 3c14985 + a9f0cbf
commit d275a9e
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Showing 3 changed files with 16 additions and 6 deletions.
diff --git a/README.md b/README.md
@@ -4,4 +4,4 @@ A microlibrary of [MTL](https://github.com/typelevel/cats-mtl) typeclasses and i
 
 * `oxidized-kernel`: `ConcurrentStateful` typeclass that relaxes the laws of `Stateful`
 * `oxidized-std`: `ConcurrentStateful` for `F` via a `Ref`
-* `oxidized`: all of the above, plus `Raise` and `Stateful` via an `IOLocal` for `IO`
+* `oxidized`: all of the above, plus `Raise`, `Local` and `Stateful` via an `IOLocal` for `IO`
diff --git a/core/src/main/scala/oxidized/instances/io.scala b/core/src/main/scala/oxidized/instances/io.scala
@@ -16,12 +16,10 @@
 
 package oxidized.instances
 
-import cats.mtl.Stateful
+import cats.mtl.{Local, Raise, Stateful}
 import cats.effect.IO
-import cats.Monad
+import cats.{Applicative, Functor, Monad}
 import cats.effect.IOLocal
-import cats.mtl.Raise
-import cats.Functor
 
 object io extends IOInstances
 
@@ -33,6 +31,17 @@ trait IOInstances {
       override def set(s: A): IO[Unit] = local.set(s)
     }
 
+  implicit def catsMtlEffectLocalForIO[E](implicit ioLocal: IOLocal[E]): Local[IO, E] =
+    new Local[IO, E] {
+      override def local[A](fa: IO[A])(f: E => E): IO[A] = ioLocal.get.flatMap { initial =>
+        ioLocal.set(f(initial)) >> fa.guarantee(ioLocal.set(initial))
+      }
+
+      override def applicative: Applicative[IO] = IO.asyncForIO
+
+      override def ask[E2 >: E]: IO[E2] = ioLocal.get
+    }
+
   implicit def catsMtlEffectRaiseForIO: Raise[IO, Throwable] =
     new Raise[IO, Throwable] {
       override def functor: Functor[IO] = IO.asyncForIO

diff --git a/core/src/test/scala/oxidized/instances/IOSpec.scala b/core/src/test/scala/oxidized/instances/IOSpec.scala
@@ -17,7 +17,7 @@
 package oxidized.instances
 
 import cats.effect.testkit.TestInstances
-import cats.mtl.laws.discipline.{HandleTests, StatefulTests}
+import cats.mtl.laws.discipline.{HandleTests, LocalTests, StatefulTests}
 import cats.effect.IOLocal
 import cats.effect.IO
 import org.specs2.mutable.Specification
@@ -35,6 +35,7 @@ class IOSpec extends Specification with Discipline with TestInstances {
     case _ => throw new RuntimeException
   }
   checkAll("Stateful[IO]", StatefulTests[IO, Int].stateful)
+  checkAll("Local[IO]", LocalTests[IO, Int].local[Int, Int])
   checkAll("Handle[IO]", HandleTests[IO, Throwable].handle[Int])
 
 }