introduce retry on Either.Left

arrow-libs/resilience/arrow-resilience/src/commonMain/kotlin/arrow/resilience/ScheduleEither.kt

@@ -0,0 +1,30 @@
+import arrow.core.Either
+import arrow.core.raise.Raise
+import arrow.core.raise.either
+import arrow.resilience.Schedule
+import arrow.resilience.ScheduleStep
+import kotlinx.coroutines.currentCoroutineContext
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.ensureActive
+import kotlin.time.Duration
+
+public suspend fun <Error, Result, Output> Schedule<Error, Output>.retry(
+  action: suspend Raise<Error>.() -> Result,
+): Either<Error, Result> {
+  var step: ScheduleStep<Error, Output> = step
+
+  while (true) {
+    currentCoroutineContext().ensureActive()
+    when (val result = either { action() }) {
+      is Either.Right -> return result
+      is Either.Left -> when (val decision = step(result.value)) {
+        is Schedule.Decision.Continue -> {
+          if (decision.delay != Duration.ZERO) delay(decision.delay)
+          step = decision.step
+        }
+
+        is Schedule.Decision.Done -> return result
+      }
+    }
+  }
+}

arrow-libs/resilience/arrow-resilience/src/commonTest/kotlin/arrow/resilience/ScheduleEitherKtTest.kt

@@ -0,0 +1,36 @@
+package arrow.resilience
+
+import arrow.atomic.AtomicLong
+import arrow.core.Either
+import kotlinx.coroutines.test.TestResult
+import kotlinx.coroutines.test.runTest
+import retry
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class ScheduleEitherKtTest {
+
+  @Test
+  fun retryIsStackSafe(): TestResult = runTest {
+    val count = AtomicLong(0)
+    val iterations = 20_000L
+
+    val result = Schedule.recurs<CustomError>(iterations).retry {
+      count.incrementAndGet()
+      raise(CustomError)
+    }
+
+    assertTrue { result is Either.Left }
+    assertEquals(iterations + 1, count.get())
+  }
+
+  @Test
+  fun retrySucceedsIfRightIsReturned(): TestResult = runTest {
+    val result = Schedule.recurs<CustomError>(0).retry { 1 }
+
+    assertTrue { result is Either.Right && result.value == 1 }
+  }
+}
+
+private object CustomError