traverse and sequence for View

js7-base/shared/src/main/scala/js7/base/utils/CatsUtils.scala

@@ -149,6 +149,28 @@ object CatsUtils:
       : G[F[B]] =
         fa.traverse(f).map(_.flatten)
 
+    extension [L, R](view: View[Either[L, R]])
+      /** A fail-fast specialization of sequence for View: */
+      def sequence: Either[L, Vector[R]] =
+        val builder = Vector.newBuilder[R]
+        val it = view.iterator
+        while it.hasNext do
+          it.next() match
+            case Left(l) => return Left(l)
+            case Right(r) => builder += r
+        Right(builder.result())
+
+    extension [A](view: View[A])
+      /** A fail-fast specialization of traverse for View: */
+      def traverse[L, R](f: A => Either[L, R]): Either[L, Vector[R]] =
+        val builder = Vector.newBuilder[R]
+        val it = view.iterator
+        while it.hasNext do
+          f(it.next()) match
+            case Left(l) => return Left(l)
+            case Right(r) => builder += r
+        Right(builder.result())
+
     extension [A](nonEmptyList: NonEmptyList[A])
       def view: View[A] = nonEmptyList.toList.view
 

js7-base/shared/src/test/scala/js7/base/problem/ProblemTest.scala

@@ -1,6 +1,7 @@
 package js7.base.problem
 
 import cats.syntax.semigroup.*
+import cats.syntax.traverse.*
 import js7.base.circeutils.CirceUtils.*
 import js7.base.problem.ProblemTest.*
 import js7.base.test.OurTestSuite
@@ -241,6 +242,15 @@ final class ProblemTest extends OurTestSuite:
       case Problem.IsThrowable(_: IllegalStateException) => fail()
       case _ =>
 
+  "sequence" in:
+    val listOfChecked = List(Right(1), Left(Problem("FIRST")), Right(2), Left(Problem("MORE")))
+    assert(listOfChecked.sequence == List(Left(Problem("FIRST"))))
+
+  "traverse" in:
+    def f(i: Int) = if i % 2 != 0 then Left(Problem(s"$i is not even")) else Right(100 * i)
+    val list = List(1, 2, 3, 4, 5)
+    assert(list.traverse(f) == Left(Problem("1 is not even")))
+
   private def catch_(problem: Problem): String =
     intercept[ProblemException] { throw problem.throwable } .toStringWithCauses
 

js7-base/shared/src/test/scala/js7/base/utils/CatsTest.scala

@@ -0,0 +1,11 @@
+package js7.base.utils
+
+import cats.syntax.traverse.*
+import js7.base.test.OurTestSuite
+import js7.base.utils.ScalaUtils.syntax.*
+
+final class CatsTest extends OurTestSuite:
+
+  "sequence" in:
+    val list = List(Left(1), Right(2), Left(3), Right(4))
+    assert(list.sequence == Left(1))

js7-base/shared/src/test/scala/js7/base/utils/CatsUtilsTest.scala

@@ -9,7 +9,6 @@ import js7.base.catsutils.CatsEffectExtensions.joinStd
 import js7.base.problem.{Problem, ProblemException}
 import js7.base.test.OurAsyncTestSuite
 import js7.base.utils.CatsUtils.*
-import js7.base.utils.CatsUtils.syntax.traverseFlat
 
 /**
   * @author Joacim Zschimmer
@@ -54,6 +53,8 @@ final class CatsUtilsTest extends OurAsyncTestSuite:
 
   "F[A]" - {
     "traverseFlat(f) == traverse(f).map(_.flatten)" in:
+      import js7.base.utils.CatsUtils.syntax.traverseFlat
+
       def f(i: Int): Either[String, List[Int]] =
         if i < 0 then
           Left("NEGATIVE")
@@ -83,3 +84,28 @@ final class CatsUtilsTest extends OurAsyncTestSuite:
       assertDoesNotCompile("List(1, 2, 3).traverseFlat(g)")
       assert(List(1, 2, 3).traverse(g).map(_.flatten) == Right(List(1, 2, 2, 3, 3, 3)))
   }
+
+  "View[Either[L, R]]" - {
+    def f(i: Int): Either[String, Int] =
+      if i % 2 == 1 then Left(s"$i is not even") else Right(100 * i)
+
+    "sequence" in:
+      import js7.base.utils.CatsUtils.syntax.sequence
+
+      val lazyList = LazyList.from(1).map(f)
+      assert(lazyList.sequence == Left("1 is not even"))
+
+      val list = List(Left(1), Right(2), Left(3), Right(4))
+      assert(list.view.sequence == Left(1))
+      assert(list.sequence == Left(1))
+
+    "traverse" in:
+      import js7.base.utils.CatsUtils.syntax.traverse
+
+      val lazyList = LazyList.from(1)
+      assert(lazyList.traverse(f) == Left("1 is not even"))
+
+      val list = List(1, 2, 3, 4)
+      assert(list.view.traverse(f) == Left("1 is not even"))
+      assert(list.traverse(f) == Left("1 is not even"))
+  }