Backport Raise & error handlers

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/Option.kt

@@ -2,6 +2,8 @@
 package arrow.core
 
 import arrow.core.Either.Right
+import arrow.core.raise.OptionRaise
+import arrow.core.raise.option
 import arrow.typeclasses.Monoid
 import arrow.typeclasses.Semigroup
 import kotlin.contracts.ExperimentalContracts
@@ -12,7 +14,7 @@ import kotlin.jvm.JvmName
 import kotlin.jvm.JvmStatic
 
 /**
- *
+ * <!--- TEST_NAME OptionKnitTest -->
  *
  * If you have worked with Java at all in the past, it is very likely that you have come across a `NullPointerException` at some time (other languages will throw similarly named errors in such a case). Usually this happens because some method returns `null` when you weren't expecting it and, thus, isn't dealing with that possibility in your client code. A value of `null` is often abused to represent an absent optional value.
  * Kotlin tries to solve the problem by getting rid of `null` values altogether, and providing its own special syntax [Null-safety machinery based on `?`](https://kotlinlang.org/docs/reference/null-safety.html).
@@ -457,6 +459,7 @@ public sealed class Option<out A> {
         f()
         this
       }
+
       is Some -> this
     }
   }
@@ -706,6 +709,7 @@ public sealed class Option<out A> {
         None -> None
         is Some -> Some(b.value.rightIor())
       }
+
       is Some -> when (b) {
         None -> Some(this.value.leftIor())
         is Some -> Some(Pair(this.value, b.value).bothIor())
@@ -1017,6 +1021,7 @@ public inline fun <A> Option<A>.ensure(error: () -> Unit, predicate: (A) -> Bool
         error()
         None
       }
+
     is None -> this
   }
 }
@@ -1103,14 +1108,20 @@ public fun <A, B> Option<Validated<A, B>>.separateValidated(): Pair<Option<A>, O
 public fun <A> Option<Iterable<A>>.sequence(): List<Option<A>> =
   traverse(::identity)
 
-@Deprecated("sequenceEither is being renamed to sequence to simplify the Arrow API", ReplaceWith("sequence()", "arrow.core.sequence"))
+@Deprecated(
+  "sequenceEither is being renamed to sequence to simplify the Arrow API",
+  ReplaceWith("sequence()", "arrow.core.sequence")
+)
 public fun <A, B> Option<Either<A, B>>.sequenceEither(): Either<A, Option<B>> =
   sequence()
 
 public fun <A, B> Option<Either<A, B>>.sequence(): Either<A, Option<B>> =
   traverse(::identity)
 
-@Deprecated("sequenceValidated is being renamed to sequence to simplify the Arrow API", ReplaceWith("sequence()", "arrow.core.sequence"))
+@Deprecated(
+  "sequenceValidated is being renamed to sequence to simplify the Arrow API",
+  ReplaceWith("sequence()", "arrow.core.sequence")
+)
 public fun <A, B> Option<Validated<A, B>>.sequenceValidated(): Validated<A, Option<B>> =
   sequence()
 
@@ -1185,6 +1196,7 @@ public fun <A> Option<A>.combine(SGA: Semigroup<A>, b: Option<A>): Option<A> =
       is Some -> Some(SGA.run { value.combine(b.value) })
       None -> this
     }
+
     None -> b
   }
 
@@ -1194,3 +1206,53 @@ public operator fun <A : Comparable<A>> Option<A>.compareTo(other: Option<A>): I
     other.fold({ 1 }, { a2 -> a1.compareTo(a2) })
   }
 )
+
+/**
+ * Recover from any [None] if encountered.
+ *
+ * The recover DSL allows you to recover from any [None] value by:
+ *  - Computing a fallback value [A]
+ *  - Shifting a _new error_ of [None] into the [Option].
+ *
+ * ```kotlin
+ * import arrow.core.Option
+ * import arrow.core.none
+ * import arrow.core.Some
+ * import arrow.core.recover
+ * import io.kotest.matchers.shouldBe
+ *
+ * fun test() {
+ *   val error: Option<Int> = none()
+ *   val fallback: Option<Int> = error.recover { 5 }
+ *   fallback shouldBe Some(5)
+ * }
+ * ```
+ * <!--- KNIT example-option-24.kt -->
+ * <!--- TEST lines.isEmpty() -->
+ *
+ * When shifting a new error [None] into the [Option]:
+ *
+ * ```kotlin
+ * import arrow.core.Option
+ * import arrow.core.none
+ * import arrow.core.Some
+ * import arrow.core.recover
+ * import io.kotest.matchers.shouldBe
+ *
+ * fun test() {
+ *   val error: Option<Int> = none()
+ *   fun fallback(): Option<Int> = Some(5)
+ *   fun failure(): Option<Int> = none()
+ *
+ *   error.recover { fallback().bind() } shouldBe Some(5)
+ *   error.recover { failure().bind() } shouldBe none()
+ * }
+ * ```
+ * <!--- KNIT example-option-25.kt -->
+ * <!--- TEST lines.isEmpty() -->
+ */
+public inline fun <A> Option<A>.recover(recover: OptionRaise.(None) -> A): Option<A> =
+  when (this@recover) {
+    is None -> option { recover(this, None) }
+    is Some -> this@recover
+  }

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/computations/either.kt

@@ -11,26 +11,29 @@ import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
 import kotlin.coroutines.RestrictsSuspension
 
-@Deprecated(deprecateInFavorOfEffectScope, ReplaceWith("EffectScope<E>", "arrow.core.continuations.EffectScope"))
+@Deprecated(
+  "EitherEffect is replaced with arrow.core.raise.Raise<E>",
+  ReplaceWith("Raise<E>", "arrow.core.raise.Raise")
+)
 public fun interface EitherEffect<E, A> : Effect<Either<E, A>> {
-
+  
   public suspend fun <B> Either<E, B>.bind(): B =
     when (this) {
       is Either.Right -> value
       is Left -> control().shift(this@bind)
     }
-
+  
   public suspend fun <B> Validated<E, B>.bind(): B =
     when (this) {
       is Validated.Valid -> value
       is Validated.Invalid -> control().shift(Left(value))
     }
-
+  
   public suspend fun <B> Result<B>.bind(transform: (Throwable) -> E): B =
     fold(::identity) { throwable ->
       control().shift(transform(throwable).left())
     }
-
+  
   /**
    * Ensure check if the [value] is `true`,
    * and if it is it allows the `either { }` binding to continue.
@@ -85,34 +88,41 @@ public fun interface EitherEffect<E, A> : Effect<Either<E, A>> {
  * ```
  * <!--- KNIT example-either-computations-02.kt -->
  */
-@Deprecated(deprecateInFavorOfEffectScope)
+@Deprecated(
+  "Replaced by Raise, replace arrow.core.computations.ensureNotNull to arrow.core.raise.ensureNotNull",
+  ReplaceWith(
+    "ensureNotNull(value, orLeft)",
+    "import arrow.core.raise.ensureNotNull"
+  )
+)
 @OptIn(ExperimentalContracts::class) // Contracts not available on open functions, so made it top-level.
 public suspend fun <E, B : Any> EitherEffect<E, *>.ensureNotNull(value: B?, orLeft: () -> E): B {
   contract {
     returns() implies (value != null)
   }
-
+  
   return value ?: orLeft().left().bind()
 }
 
-@Deprecated(deprecatedInFavorOfEagerEffectScope, ReplaceWith("EagerEffectScope<E>", "arrow.core.continuations.EagerEffectScope"))
+@Deprecated(
+  "RestrictedEitherEffect is replaced with arrow.core.raise.Raise<E>",
+  ReplaceWith("Raise<E>", "arrow.core.raise.Raise")
+)
 @RestrictsSuspension
 public fun interface RestrictedEitherEffect<E, A> : EitherEffect<E, A>
 
-@Deprecated(deprecateInFavorOfEffectOrEagerEffect, ReplaceWith("either", "arrow.core.continuations.either"))
+@Deprecated(eitherDSLDeprecation, ReplaceWith("either", "arrow.core.raise.either"))
 @Suppress("ClassName")
 public object either {
-  @Deprecated(deprecateInFavorOfEagerEffect, ReplaceWith("either.eager(c)", "arrow.core.continuations.either"))
+  @Deprecated(eitherDSLDeprecation, ReplaceWith("either(c)", "arrow.core.raise.either"))
   public inline fun <E, A> eager(crossinline c: suspend RestrictedEitherEffect<E, *>.() -> A): Either<E, A> =
     Effect.restricted(eff = { RestrictedEitherEffect { it } }, f = c, just = { it.right() })
-
-  @Deprecated(deprecateInFavorOfEffect, ReplaceWith("either(c)", "arrow.core.continuations.either"))
+  
+  @Deprecated(eitherDSLDeprecation, ReplaceWith("either(c)", "arrow.core.raise.either"))
   public suspend inline operator fun <E, A> invoke(crossinline c: suspend EitherEffect<E, *>.() -> A): Either<E, A> =
     Effect.suspended(eff = { EitherEffect { it } }, f = c, just = { it.right() })
 }
 
-internal const val deprecatedInFavorOfEagerEffectScope: String = "Deprecated in favor of Eager Effect DSL: EagerEffectScope"
-internal const val deprecateInFavorOfEffectScope: String = "Deprecated in favor of Effect DSL: EffectScope"
-internal const val deprecateInFavorOfEffect: String = "Deprecated in favor of the Effect Runtime"
-internal const val deprecateInFavorOfEagerEffect: String = "Deprecated in favor of the EagerEffect Runtime"
-internal const val deprecateInFavorOfEffectOrEagerEffect: String = "Deprecated in favor of the Effect or EagerEffect Runtime"
+private const val eitherDSLDeprecation =
+  "The either DSL has been moved to arrow.core.raise.either.\n" +
+    "Replace import arrow.core.computations.* with arrow.core.raise.*"

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/computations/eval.kt

@@ -4,24 +4,28 @@ import arrow.continuations.Effect
 import arrow.core.Eval
 import kotlin.coroutines.RestrictsSuspension
 
-@Deprecated(deprecateInFavorOfEffectScope, ReplaceWith("EffectScope<E>", "arrow.core.continuations.EffectScope"))
+@Deprecated("EvalEffect is redundant. Use Eval#value directly instead")
 public fun interface EvalEffect<A> : Effect<Eval<A>> {
+  @Deprecated(
+    "EvalEffect is redundant. Use Eval#value directly instead",
+    ReplaceWith("this.value()")
+  )
   public suspend fun <B> Eval<B>.bind(): B =
     value()
 }
 
-@Deprecated(deprecatedInFavorOfEagerEffectScope, ReplaceWith("EagerEffectScope<E>", "arrow.core.continuations.EagerEffectScope"))
+@Deprecated("RestrictedEvalEffect is redundant. Use Eval#value directly instead")
 @RestrictsSuspension
 public fun interface RestrictedEvalEffect<A> : EvalEffect<A>
 
-@Deprecated(deprecateInFavorOfEffectOrEagerEffect)
+@Deprecated("EvalEffect is redundant. Use Eval#value directly instead")
 @Suppress("ClassName")
 public object eval {
-  @Deprecated(deprecateInFavorOfEagerEffect, ReplaceWith("eagerEffect(func)", "arrow.core.continuations.eagerEffect"))
+  @Deprecated("EvalEffect is redundant. Use Eval#value directly instead")
   public inline fun <A> eager(crossinline func: suspend RestrictedEvalEffect<A>.() -> A): Eval<A> =
     Effect.restricted(eff = { RestrictedEvalEffect { it } }, f = func, just = Eval.Companion::now)
-
-  @Deprecated(deprecateInFavorOfEffect, ReplaceWith("effect(func)", "arrow.core.continuations.effect"))
+  
+  @Deprecated("EvalEffect is redundant. Use Eval#value) directly instead")
   public suspend inline operator fun <A> invoke(crossinline func: suspend EvalEffect<*>.() -> A): Eval<A> =
     Effect.suspended(eff = { EvalEffect { it } }, f = func, just = Eval.Companion::now)
 }

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/computations/nullable.kt

@@ -7,7 +7,10 @@ import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
 import kotlin.coroutines.RestrictsSuspension
 
-@Deprecated(deprecateInFavorOfEffectScope)
+@Deprecated(
+  "NullableEffect<A> is replaced with arrow.core.raise.NullableRaise",
+  ReplaceWith("NullableRaise", "arrow.core.raise.NullableRaise")
+)
 public fun interface NullableEffect<A> : Effect<A?> {
   public suspend fun <B> B?.bind(): B =
     this ?: control().shift(null)
@@ -68,7 +71,13 @@ public fun interface NullableEffect<A> : Effect<A?> {
  * ```
  * <!--- KNIT example-nullable-computations-02.kt -->
  */
-@Deprecated(deprecateInFavorOfEffectScope, ReplaceWith("ensureNotNull", "arrow.core.continuations.ensureNotNull"))
+@Deprecated(
+  "Replaced by Raise, replace arrow.core.computations.ensureNotNull to arrow.core.raise.ensureNotNull",
+  ReplaceWith(
+    "ensureNotNull(value)",
+    "import arrow.core.raise.ensureNotNull"
+  )
+)
 @OptIn(ExperimentalContracts::class) // Contracts not available on open functions, so made it top-level.
 public suspend fun <B : Any> NullableEffect<*>.ensureNotNull(value: B?): B {
   contract {
@@ -78,18 +87,25 @@ public suspend fun <B : Any> NullableEffect<*>.ensureNotNull(value: B?): B {
   return value ?: control().shift(null)
 }
 
-@Deprecated(deprecatedInFavorOfEagerEffectScope)
+@Deprecated(
+  "RestrictedNullableEffect<A> is replaced with arrow.core.raise.NullableRaise",
+  ReplaceWith("NullableRaise", "arrow.core.raise.NullableRaise")
+)
 @RestrictsSuspension
 public fun interface RestrictedNullableEffect<A> : NullableEffect<A>
 
-@Deprecated(deprecateInFavorOfEffectOrEagerEffect, ReplaceWith("nullable", "arrow.core.continuations.nullable"))
+@Deprecated(nullableDSLDeprecation, ReplaceWith("nullable", "arrow.core.raise.nullable"))
 @Suppress("ClassName")
 public object nullable {
-  @Deprecated(deprecateInFavorOfEagerEffect, ReplaceWith("nullable.eager(func)", "arrow.core.continuations.nullable"))
+  @Deprecated(nullableDSLDeprecation, ReplaceWith("nullable(func)", "arrow.core.raise.nullable"))
   public inline fun <A> eager(crossinline func: suspend RestrictedNullableEffect<A>.() -> A?): A? =
     Effect.restricted(eff = { RestrictedNullableEffect { it } }, f = func, just = { it })
-
-  @Deprecated(deprecateInFavorOfEffect, ReplaceWith("nullable(func)", "arrow.core.continuations.nullable"))
+  
+  @Deprecated(nullableDSLDeprecation, ReplaceWith("nullable(func)", "arrow.core.raise.nullable"))
   public suspend inline operator fun <A> invoke(crossinline func: suspend NullableEffect<*>.() -> A?): A? =
     Effect.suspended(eff = { NullableEffect { it } }, f = func, just = { it })
 }
+
+private const val nullableDSLDeprecation =
+  "The nullable DSL has been moved to arrow.core.raise.nullable.\n" +
+    "Replace import arrow.core.computations.* with arrow.core.raise.*"

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/computations/option.kt

@@ -8,7 +8,10 @@ import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
 import kotlin.coroutines.RestrictsSuspension
 
-@Deprecated(deprecateInFavorOfEffectScope, ReplaceWith("EffectScope<E>", "arrow.core.continuations.EffectScope"))
+@Deprecated(
+  "OptionEffect<A> is replaced with arrow.core.raise.OptionRaise",
+  ReplaceWith("OptionRaise", "arrow.core.raise.OptionRaise")
+)
 public fun interface OptionEffect<A> : Effect<Option<A>> {
   public suspend fun <B> Option<B>.bind(): B =
     fold({ control().shift(None) }, ::identity)
@@ -66,7 +69,13 @@ public fun interface OptionEffect<A> : Effect<Option<A>> {
  * ```
  * <!--- KNIT example-option-computations-02.kt -->
  */
-@Deprecated(deprecateInFavorOfEffectScope)
+@Deprecated(
+  "Replaced by Raise, replace arrow.core.computations.ensureNotNull to arrow.core.raise.ensureNotNull",
+  ReplaceWith(
+    "ensureNotNull(value)",
+    "import arrow.core.raise.ensureNotNull"
+  )
+)
 @OptIn(ExperimentalContracts::class) // Contracts not available on open functions, so made it top-level.
 public suspend fun <B : Any> OptionEffect<*>.ensureNotNull(value: B?): B {
   contract {
@@ -76,18 +85,32 @@ public suspend fun <B : Any> OptionEffect<*>.ensureNotNull(value: B?): B {
   return value ?: (this as OptionEffect<Any?>).control().shift(None)
 }
 
-@Deprecated(deprecatedInFavorOfEagerEffectScope, ReplaceWith("EagerEffectScope<E>", "arrow.core.continuations.EagerEffectScope"))
-@RestrictsSuspension
+@Deprecated(
+  "RestrictedEitherEffect is replaced with arrow.core.raise.OptionRaise",
+  ReplaceWith("OptionRaise", "arrow.core.raise.OptionRaise")
+)@RestrictsSuspension
 public fun interface RestrictedOptionEffect<A> : OptionEffect<A>
 
-@Deprecated(deprecateInFavorOfEffectOrEagerEffect, ReplaceWith("option", "arrow.core.continuations.option"))
+@Deprecated(
+  optionDSLDeprecation,
+  ReplaceWith("option", "arrow.core.raise.option")
+)
 @Suppress("ClassName")
 public object option {
-  @Deprecated(deprecateInFavorOfEagerEffect, ReplaceWith("option.eager(func)", "arrow.core.continuations.option"))
+  @Deprecated(
+    optionDSLDeprecation,
+    ReplaceWith("option(func)", "arrow.core.raise.option")
+  )
   public inline fun <A> eager(crossinline func: suspend RestrictedOptionEffect<A>.() -> A): Option<A> =
     Effect.restricted(eff = { RestrictedOptionEffect { it } }, f = func, just = { Option.fromNullable(it) })
-
-  @Deprecated(deprecateInFavorOfEffect, ReplaceWith("option(func)", "arrow.core.continuations.option"))
-  public suspend inline operator fun <A> invoke(crossinline func: suspend OptionEffect<*>.() -> A?): Option<A> =
+
+  @Deprecated(
+    optionDSLDeprecation,
+    ReplaceWith("option(func)", "arrow.core.raise.option")
+  )  public suspend inline operator fun <A> invoke(crossinline func: suspend OptionEffect<*>.() -> A?): Option<A> =
     Effect.suspended(eff = { OptionEffect { it } }, f = func, just = { Option.fromNullable(it) })
 }
+
+private const val optionDSLDeprecation =
+  "The option DSL has been moved to arrow.core.raise.option.\n" +
+    "Replace import arrow.core.computations.* with arrow.core.raise.*"