automatic typeclass derivation

build.sbt

@@ -18,7 +18,7 @@ val pureconfigVersion = "0.9.0"
 val shapelessVersion = "2.3.3"
 val scalaCheckVersion = "1.13.5"
 val scalaXmlVersion = "1.0.6"
-val scalazVersion = "7.2.19"
+val scalazVersion = "7.2.20"
 val scodecVersion = "1.10.3"
 
 val macroParadise =

modules/scalaz/shared/src/main/scala/eu/timepit/refined/scalaz/package.scala

@@ -1,10 +1,11 @@
+// Copyright: 2015 - 2018 Frank S. Thomas and Sam Halliday
+// License: https://opensource.org/licenses/MIT
+
 package eu.timepit.refined
 
-import _root_.scalaz.Equal
-import _root_.scalaz.Show
-import _root_.scalaz.@@
+import _root_.scalaz.{@@, Contravariant, Equal, MonadError, Show}
 import _root_.scalaz.syntax.contravariant._
-import eu.timepit.refined.api.RefType
+import eu.timepit.refined.api.{RefType, Validate}
 import scala.reflect.macros.blackbox
 
 package object scalaz {
@@ -42,4 +43,33 @@ package object scalaz {
    */
   implicit def refTypeShow[F[_, _], T: Show, P](implicit rt: RefType[F]): Show[F[T, P]] =
     Show[T].contramap(rt.unwrap)
+
+  /**
+   * Instances for typeclasses with a `Contravariant`, e.g. encoders.
+   */
+  implicit def refTypeContravariant[R[_, _], F[_], A, B](
+      implicit
+      C: Contravariant[F],
+      R: RefType[R],
+      F: F[A]
+  ): F[R[A, B]] = C.contramap(F)(R.unwrap)
+
+  /**
+   * Instances for typeclasses with a `MonadError[?, String]`, i.e. a
+   * disjunction kleisli arrow applied to the typeclass. e.g. decoders.
+   */
+  implicit def refTypeMonadError[R[_, _], F[_], A, B](
+      implicit
+      M: MonadError[F, String],
+      R: RefType[R],
+      V: Validate[A, B],
+      F: F[A]
+  ): F[R[A, B]] =
+    M.bind(F) { f =>
+      R.refine(f) match {
+        case Left(s)  => M.raiseError(s)
+        case Right(v) => M.pure(v)
+      }
+    }
+
 }

modules/scalaz/shared/src/test/scala-2.12/eu/timepit/refined/scalaz/RefTypeSpecScalazMonadError.scala

@@ -0,0 +1,57 @@
+// Copyright: 2018 Sam Halliday
+// License: https://opensource.org/licenses/MIT
+
+package eu.timepit.refined.scalaz
+
+import _root_.scalaz.{@@, \/, IsomorphismMonadError, MonadError, ReaderT}
+import _root_.scalaz.Isomorphism.{<~>, IsoFunctorTemplate}
+import _root_.scalaz.syntax.either._
+import eu.timepit.refined.api._
+import eu.timepit.refined.collection._
+import org.scalacheck._
+import org.scalacheck.Prop._
+
+trait Decoder[A] {
+  def decode(s: String): String \/ A
+}
+object Decoder {
+  @inline def apply[A](implicit A: Decoder[A]): Decoder[A] = A
+  @inline def instance[A](f: String => String \/ A): Decoder[A] =
+    new Decoder[A] {
+      override def decode(s: String): String \/ A = f(s)
+    }
+
+  implicit val string: Decoder[String] = instance(_.right)
+
+  type Out[a] = String \/ a
+  type MT[a] = ReaderT[Out, String, a]
+  implicit val isoReaderT: Decoder <~> MT =
+    new IsoFunctorTemplate[Decoder, MT] {
+      def from[A](fa: MT[A]) = instance(fa.run(_))
+      def to[A](fa: Decoder[A]) = ReaderT[Out, String, A](fa.decode)
+    }
+  // will be cleaner after https://github.com/scalaz/scalaz/pull/1661
+  private[this] val ME = MonadError[MT, String]
+  implicit def monad: MonadError[Decoder, String] =
+    new IsomorphismMonadError[Decoder, MT, String] {
+      override implicit val G: MonadError[MT, String] = ME
+      override val iso: Decoder <~> MT = isoReaderT
+    }
+}
+
+class RefTypeSpecScalazMonadError extends Properties("scalaz.Contravariant") {
+  // annoying that this import is needed!
+  // https://github.com/scala/bug/issues/10753#issuecomment-369592913
+  import Decoder.monad
+
+  property("Refined via scalaz.MonadError[?, String]") = secure {
+    val decoder = Decoder[String Refined NonEmpty]
+    decoder.decode("").isLeft && decoder.decode("hello world").isRight
+  }
+
+  property("@@ via scalaz.MonadError[?, String]") = secure {
+    val decoder = Decoder[String @@ NonEmpty]
+    decoder.decode("").isLeft && decoder.decode("hello world").isRight
+  }
+
+}

modules/scalaz/shared/src/test/scala/eu/timepit/refined/scalaz/RefTypeSpecScalazContravariant.scala

@@ -0,0 +1,51 @@
+// Copyright: 2018 Sam Halliday
+// License: https://opensource.org/licenses/MIT
+
+package eu.timepit.refined.scalaz
+
+import _root_.scalaz.{@@, Contravariant}
+import eu.timepit.refined.api._
+import eu.timepit.refined.collection._
+import org.scalacheck._
+import org.scalacheck.Prop._
+
+trait Encoder[A] {
+  def encode(a: A): String
+}
+object Encoder {
+  @inline def apply[A](implicit A: Encoder[A]): Encoder[A] = A
+  @inline def instance[A](f: A => String): Encoder[A] = new Encoder[A] {
+    override def encode(a: A): String = f(a)
+  }
+
+  implicit val string: Encoder[String] = instance(identity)
+
+  implicit val contravariant: Contravariant[Encoder] =
+    new Contravariant[Encoder] {
+      override def contramap[A, B](fa: Encoder[A])(f: B => A): Encoder[B] =
+        instance(b => fa.encode(f(b)))
+    }
+}
+
+class RefTypeSpecScalazContravariant extends Properties("scalaz.Contravariant") {
+  // annoying that this import is needed!
+  // https://github.com/scala/bug/issues/10753#issuecomment-369592913
+  import Encoder._
+
+  property("Refined via scalaz.Contravariant") = secure {
+    import eu.timepit.refined.auto._
+
+    val x: String Refined NonEmpty = "hello world"
+
+    Encoder[String Refined NonEmpty].encode(x) == "hello world"
+  }
+
+  property("@@ via scalaz.Contravariant") = secure {
+    import eu.timepit.refined.scalaz.auto._
+
+    val x: String @@ NonEmpty = "hello world"
+
+    Encoder[String @@ NonEmpty].encode(x) == "hello world"
+  }
+
+}