add Option syntax

Author: satorg

core/src/main/scala/cats/mtl/syntax/all.scala

@@ -27,3 +27,4 @@ trait AllSyntax
     with TellSyntax
     with HandleSyntax
     with ChronicleSyntax
+    with OptionSyntax

core/src/main/scala/cats/mtl/syntax/option.scala

@@ -0,0 +1,106 @@
+/*
+ * Copyright 2021 Typelevel
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cats
+package mtl
+package syntax
+
+object option extends OptionSyntax
+
+private[mtl] trait OptionSyntax {
+  implicit def catsMtsSyntaxToOptionOps[A](oa: Option[A]): OptionOps[A] = new OptionOps[A](oa)
+}
+
+final class OptionOps[A] private[mtl] (private val self: Option[A]) extends AnyVal {
+  import OptionOps.*
+
+  /**
+   * Lifts `Option[A]` to `F[A]` as long as there's `Raise[F, E]` in the scope and `F` is an
+   * `Applicative`, with `E` used as the error value when the `Option` is empty.
+   *
+   * @note
+   *   method `.rescue` in the example requires `ApplicativeError[F, E]` instance.
+   *
+   * @example
+   *   (Scala 3)
+   *   {{{
+   *   import scala.util.*
+   *   import cats.mtl.*, syntax.option.*
+   *
+   *   case class MyErr(err: String) extends Exception(err)
+   *
+   *   val res1 =
+   *     Handle.allow:
+   *       Some(123).liftTo[Try]("OOPS")
+   *     .rescue: err =>
+   *       Failure(MyErr(err))
+   *
+   *   assertEquals(res1, Success(123))
+   *
+   *   val res2 =
+   *     Handle.allow:
+   *       None.liftTo[Try]("OOPS")
+   *     .rescue: err =>
+   *       Failure(MyErr(err))
+   *
+   *   assertEquals(res2, Failure(MyErr("OOPS")))
+   *   }}}
+   */
+  def liftTo[F[_]]: LiftToPartiallyApplied[F, A] =
+    new LiftToPartiallyApplied(self)
+
+  /**
+   * Raises `Option[A]` to `F[Unit]` as an error when present as long as there's `Raise[F, A]`
+   * in the scope and `F` is an `Applicative`
+   *
+   * @note
+   *   method `.rescue` in the example requires `ApplicativeError[F, E]` instance.
+   *
+   * @example
+   *   (Scala 3)
+   *   {{{
+   *   import scala.util.*
+   *   import cats.mtl.*, syntax.option.*
+   *
+   *   case class MyErr(err: String) extends Exception(err)
+   *
+   *   val res1 =
+   *     Handle.allow:
+   *       Some("OOPS").raiseTo[Try]
+   *     .rescue: err =>
+   *       Failure(MyErr(err))
+   *
+   *   assertEquals(res1, Failure(MyErr("OOPS")))
+   *
+   *   val res2 =
+   *     Handle.allow:
+   *       (None: Option[String]).raiseTo[Try]
+   *     .rescue: err =>
+   *       Failure(MyErr(err))
+   *
+   *   assertEquals(res2, Success(()))
+   *   }}}
+   */
+  def raiseTo[F[_]](implicit F: Applicative[F], raise: Raise[F, A]): F[Unit] =
+    self.fold(F.unit)(raise.raise)
+}
+
+object OptionOps {
+  final class LiftToPartiallyApplied[F[_], A](private val self: Option[A]) extends AnyVal {
+    def apply[E](ifEmpty: => E)(implicit F: Applicative[F], raise: Raise[F, E]): F[A] =
+      raise.fromOption(self)(ifEmpty)
+  }
+}

tests/shared/src/test/scala/cats/mtl/tests/Syntax.scala

@@ -70,6 +70,20 @@ final class Syntax extends BaseSuite {
         bar[F] *> Bar(42).raise
 
       val _ = foo[Either[Foo, *]]
+
+      def fooWithApplicativeError[F[_]](implicit
+          // `Applicative` is required by `liftTo`.
+          // `ApplicativeError` is used to enforce checks for non-ambiguity.
+          F: ApplicativeError[F, Foo],
+          raise: Raise[F, Foo]): Unit = {
+
+        val _ = (
+          Some("abc").liftTo[F](Bar(123)): F[String],
+          Some(Bar(456)).raiseTo[F]: F[Unit]
+        )
+      }
+
+      fooWithApplicativeError[Either[Foo, *]]
     }
 
     test("Handle") {