Add Either#handleFailureWith (#101)

cashapp · Aug 5, 2024 · e5b6bad · e5b6bad
1 parent a8c6061
commit e5b6bad
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diff --git a/lib/api/lib.api b/lib/api/lib.api
@@ -169,6 +169,7 @@ public final class app/cash/quiver/extensions/EitherKt {
 	public static final fun flatTap (Larrow/core/Either;Lkotlin/jvm/functions/Function1;)Larrow/core/Either;
 	public static final fun forEach (Larrow/core/Either;Lkotlin/jvm/functions/Function1;)V
 	public static final fun getRightUnit ()Larrow/core/Either;
+	public static final fun handleErrorWith (Larrow/core/Either;Lkotlin/jvm/functions/Function1;)Larrow/core/Either;
 	public static final fun leftAsOption (Larrow/core/Either;)Larrow/core/Option;
 	public static final fun leftForEach (Larrow/core/Either;Lkotlin/jvm/functions/Function1;)V
 	public static final fun mapOption (Larrow/core/Either;Lkotlin/jvm/functions/Function1;)Larrow/core/Either;

diff --git a/lib/src/main/kotlin/app/cash/quiver/extensions/Either.kt b/lib/src/main/kotlin/app/cash/quiver/extensions/Either.kt
@@ -8,8 +8,12 @@ import arrow.core.Some
 import arrow.core.flatMap
 import arrow.core.getOrElse
 import arrow.core.identity
+import arrow.core.recover
 import arrow.core.right
 import arrow.core.toOption
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 import kotlin.experimental.ExperimentalTypeInference
 import app.cash.quiver.extensions.traverse as quiverTraverse
 
@@ -287,3 +291,12 @@ inline fun <E, A, B> Either<E, A>.traverseOption(transform: (A) -> Option<B>): O
   quiverTraverse(transform)
 
 fun <E, A> Either<E, Option<A>>.sequence(): Option<Either<E, A>> = quiverTraverse(::identity)
+
+/**
+ * Recovers the left side of an Either with the supplied function
+ */
+@OptIn(ExperimentalContracts::class)
+inline fun <A, B, C> Either<A, B>.handleErrorWith(f: (A) -> Either<C, B>): Either<C, B> {
+  contract { callsInPlace(f, InvocationKind.AT_MOST_ONCE) }
+  return recover { a -> f(a).bind() }
+}
diff --git a/lib/src/test/kotlin/app/cash/quiver/extensions/EitherTest.kt b/lib/src/test/kotlin/app/cash/quiver/extensions/EitherTest.kt
@@ -11,6 +11,8 @@ import io.kotest.assertions.arrow.core.shouldBeLeft
 import io.kotest.assertions.arrow.core.shouldBeRight
 import io.kotest.assertions.arrow.core.shouldBeSome
 import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.result.shouldBeFailure
+import io.kotest.matchers.result.shouldBeSuccess
 import io.kotest.matchers.shouldBe
 import io.kotest.property.Arb
 import io.kotest.property.arbitrary.int
@@ -197,6 +199,19 @@ class EitherTest : StringSpec({
       )
     }
   }
+
+  "handleFailureWith recovers errors" {
+    1.right().handleErrorWith { Either.Left(Throwable("never happens")) }.shouldBeRight(1)
+    Throwable("sad panda").left().handleErrorWith { Throwable("even sadder").left() }
+      .shouldBeLeft().message shouldBe "even sadder"
+
+    Throwable("sad panda").left().handleErrorWith { 1.right() }
+      .shouldBeRight(1)
+
+    Throwable("sad panda").left().handleErrorWith { it.left() }
+      .shouldBeLeft().message shouldBe "sad panda"
+  }
+
 })
 
 fun testParse(s: String): ErrorOr<Int> =