Add loop test with exit and continue

Author: odersky

tests/run/loops.scala

@@ -0,0 +1,37 @@
+import scala.util.{boundary, break}
+
+object loop:
+
+  // We could use a boolean instead, but with `Ctrl` label types in using clauses are
+  // more specific.
+  enum Ctrl:
+    case Exit, Continue
+
+  inline def apply(inline op: boundary.Label[Ctrl] ?=> Unit) =
+    while boundary { op; Ctrl.Continue } == Ctrl.Continue do ()
+
+  inline def exit()(using boundary.Label[Ctrl]): Unit =
+    break(Ctrl.Exit)
+
+  inline def continue()(using boundary.Label[Ctrl]): Unit =
+    break(Ctrl.Continue)
+end loop
+
+def testLoop(xs: List[Int]) =
+  var current = xs
+  var sum = 0
+  loop:
+    if current.isEmpty then loop.exit()
+    val hd = current.head
+    current = current.tail
+    if hd == 0 then loop.exit()
+    if hd < 0 then loop.continue()
+    sum += hd
+  sum
+
+@main def Test =
+  assert(testLoop(List(1, 2, 3, -2, 4, -3, 0, 1, 2, 3)) == 10)
+  assert(testLoop(List()) == 0)
+  assert(testLoop(List(-2, -3, 0, 1)) == 0)
+
+