feat(boundaries): add a result boundary

src/main/scala/io/github/tassiLuca/boundaries/BoundaryExamples.scala

@@ -2,10 +2,15 @@ package io.github.tassiLuca.boundaries
 
 import scala.util.boundary
 import scala.util.boundary.break
+import optional.*
 
 object BoundaryExamples extends App:
 
   def firstIndex[T](xs: List[T], elem: T): Int =
     boundary:
       for (x, i) <- xs.zipWithIndex do if x == elem then break(i)
       -1
+
+  def firstColumn[T](xss: List[List[T]]): Option[List[T]] =
+    optional:
+      xss.map(_.headOption.?)

src/main/scala/io/github/tassiLuca/boundaries/ResultExamples.scala

@@ -0,0 +1,22 @@
+package io.github.tassiLuca.boundaries
+
+import io.github.tassiLuca.boundaries.result.{Ok, Result, Error}
+
+object ResultExamples extends App:
+
+  type User = String
+  type Address = String
+
+  def getUser(id: String): Result[User] =
+    Ok("Mario Rossi")
+
+  def getAddress(user: User): Result[Address] =
+    Error("The user doesn't exists")
+
+  def together(): Result[String] =
+    result:
+      val user = getUser("101").?
+      val address = getAddress(user).?
+      user + address
+
+  println(together())

src/main/scala/io/github/tassiLuca/boundaries/optional.scala

@@ -0,0 +1,12 @@
+package io.github.tassiLuca.boundaries
+
+import scala.util.boundary
+import scala.util.boundary.{Label, break}
+
+object optional:
+  inline def apply[T](inline body: Label[None.type] ?=> T): Option[T] =
+    boundary(Some(body))
+
+  extension [T](o: Option[T])
+    inline def ?(using label: Label[None.type]): T =
+      o.getOrElse(break(None))

src/main/scala/io/github/tassiLuca/boundaries/result.scala

@@ -0,0 +1,18 @@
+package io.github.tassiLuca.boundaries
+
+import scala.util.boundary
+import scala.util.boundary.{Label, break}
+
+object result:
+
+  sealed trait Result[+T]
+  case class Ok[+T](t: T) extends Result[T]
+  case class Error(e: String) extends Result[Nothing]
+
+  inline def apply[T](inline body: Label[Error] ?=> T): Result[T] =
+    boundary(Ok(body))
+
+  extension [T](r: Result[T])
+    inline def ?(using Label[Error]): T = r match
+      case Ok(t) => t
+      case e @ Error(_) => break(e)

src/test/scala/io/github/tassiLuca/boundaries/BoundaryExamplesTest.scala

@@ -1,6 +1,6 @@
 package io.github.tassiLuca.boundaries
 
-import io.github.tassiLuca.boundaries.BoundaryExamples.firstIndex
+import io.github.tassiLuca.boundaries.BoundaryExamples.{firstColumn, firstIndex}
 import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.matchers.should.Matchers.shouldBe
 
@@ -9,3 +9,8 @@ class BoundaryExamplesTest extends AnyFlatSpec:
     firstIndex(List(1, 2, 3, 4), 4) shouldBe 3
     firstIndex(List(1, 2, 3, 4), 0) shouldBe -1
   }
+
+  "BoundaryExamples.firstColumn" should "return a List with the first element of each List given in input" in {
+    firstColumn(List(List(1, 2, 3), List(3))) shouldBe Some(List(1, 3))
+    firstColumn(List(List(), List(1))) shouldBe None
+  }