Add adaptErr to ApplicativeErrorOps (#2698)

* add `adaptErr` to `ApplicativeErrorOps`, make `MonadError#adaptError` an alias for it * revert changes to ApplicativeErrorLaws/MonadErrorLaws * replace cross-dependency with duplication
typelevel · Feb 5, 2019 · d3b57b2 · d3b57b2
1 parent 356e339
commit d3b57b2
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diff --git a/core/src/main/scala/cats/MonadError.scala b/core/src/main/scala/cats/MonadError.scala
@@ -38,9 +38,13 @@ trait MonadError[F[_], E] extends ApplicativeError[F, E] with Monad[F] {
    * scala> 1.asRight[String].adaptError(pf)
    * res2: Either[String,Int] = Right(1)
    * }}}
+   *
+   * The same function is available in `ApplicativeErrorOps` as `adaptErr` - it cannot have the same
+   * name because this would result in ambiguous implicits. `adaptError` will be moved from MonadError to
+   * ApplicativeError in Cats 2.0: see [[https://github.com/typelevel/cats/issues/2685]]
    */
   def adaptError[A](fa: F[A])(pf: PartialFunction[E, E]): F[A] =
-    flatMap(attempt(fa))(_.fold(e => raiseError(pf.applyOrElse[E, E](e, _ => e)), pure))
+    recoverWith(fa)(pf.andThen(raiseError))
 
   /**
    * Inverse of `attempt`

diff --git a/core/src/main/scala/cats/syntax/applicativeError.scala b/core/src/main/scala/cats/syntax/applicativeError.scala
@@ -97,4 +97,31 @@ final class ApplicativeErrorOps[F[_], E, A](private val fa: F[A]) extends AnyVal
 
   def orElse(other: => F[A])(implicit F: ApplicativeError[F, E]): F[A] =
     F.handleErrorWith(fa)(_ => other)
+
+  /**
+   * Transform certain errors using `pf` and rethrow them.
+   * Non matching errors and successful values are not affected by this function.
+   *
+   * Example:
+   * {{{
+   * scala> import cats._, implicits._
+   *
+   * scala> def pf: PartialFunction[String, String] = { case "error" => "ERROR" }
+   *
+   * scala> "error".asLeft[Int].adaptErr(pf)
+   * res0: Either[String,Int] = Left(ERROR)
+   *
+   * scala> "err".asLeft[Int].adaptErr(pf)
+   * res1: Either[String,Int] = Left(err)
+   *
+   * scala> 1.asRight[String].adaptErr(pf)
+   * res2: Either[String,Int] = Right(1)
+   * }}}
+   *
+   * This is the same as `MonadErrorOps#adaptError`. It cannot have the same name because
+   * this would result in ambiguous implicits. `adaptError` will be moved from `MonadError`
+   * to `ApplicativeError` in Cats 2.0: see [[https://github.com/typelevel/cats/issues/2685]]
+   */
+  def adaptErr(pf: PartialFunction[E, E])(implicit F: ApplicativeError[F, E]): F[A] =
+    F.recoverWith(fa)(pf.andThen(F.raiseError))
 }