refactor(either): rename Exit to Either

Either need not be internal to this project.

BREAKING CHANGE: `Exit` is renamed to `Either`

Author: tusharmath

index.ts

@@ -1,6 +1,6 @@
 /* tslint:disable:file-name-casing */
 export {Await} from './src/main/Await'
-export {Exit} from './src/main/Exit'
+export {Either} from './src/main/Either'
 export {Fiber} from './src/main/Fiber'
 export {FIO, IO, Task, TaskR, UIO} from './src/main/FIO'
 export {FStream, Stream} from './src/main/FStream'

src/internals/Coordinate.ts

@@ -1,5 +1,5 @@
 import {Await} from '../main/Await'
-import {Exit} from '../main/Exit'
+import {Either} from '../main/Either'
 import {Fiber} from '../main/Fiber'
 import {FIO, UIO} from '../main/FIO'
 import {Ref} from '../main/Ref'
@@ -10,22 +10,25 @@ import {Ref} from '../main/Ref'
  * @ignore
  */
 export const coordinate = <E1, A1, E2, A2>(
-  exit: Exit<E1, A1>,
+  exit: Either<E1, A1>,
   fiber: Fiber<E2, A2>,
-  ref: Ref<Exit<E1, A1>>,
+  ref: Ref<Either<E1, A1>>,
   count: Ref<number>,
   await: Await<never, boolean>
 ): UIO<boolean> =>
   ref
     .set(exit)
     .chain(e =>
-      Exit.isFailure(e)
-        ? fiber.abort.and(await.set(FIO.of(true)))
-        : count
+      e.fold(
+        FIO.of(false),
+        () => fiber.abort.and(await.set(FIO.of(true))),
+        () =>
+          count
             .update(_ => _ + 1)
             .and(
               count.read.chain(value =>
                 value === 2 ? await.set(FIO.of(true)) : FIO.of(false)
               )
             )
+      )
     )

src/internals/FiberContext.ts

@@ -4,7 +4,7 @@
 
 import {ICancellable, IScheduler} from 'ts-scheduler'
 
-import {Exit} from '../main/Exit'
+import {Either} from '../main/Either'
 import {Fiber} from '../main/Fiber'
 import {FIO, UIO} from '../main/FIO'
 import {Instruction} from '../main/Instructions'
@@ -84,17 +84,15 @@ export class FiberContext<E = never, A = never> extends Fiber<E, A>
     return this
   }
 
-  public resumeAsync(cb: (exit: Exit<E, A>) => UIO<void>): UIO<void> {
-    const eee = <X>(con: (x: X) => Exit<E, A>) => (data: X) => {
+  public resumeAsync(cb: (exit: Either<E, A>) => UIO<void>): UIO<void> {
+    const eee = <X>(con: (x: X) => Either<E, A>) => (data: X) => {
       // tslint:disable-next-line: no-use-before-declare
       const cancel = () => this.cancellationList.remove(id)
       const id = this.cancellationList.push(
         this.$fork(cb(con(data)).asInstruction).$resume(cancel, cancel)
       )
     }
 
-    return FIO.uio(
-      () => void this.$resume(eee(Exit.failure), eee(Exit.success))
-    )
+    return FIO.uio(() => void this.$resume(eee(Either.left), eee(Either.right)))
   }
 }

src/internals/Id.ts

@@ -0,0 +1,5 @@
+/**
+ * Simple Id function that takes in an input and returns the same value as it is.
+ * @ignore
+ */
+export const Id = <A>(_: A): A => _

src/main/Await.ts

@@ -2,7 +2,7 @@ import {mutable} from 'standard-data-structures'
 
 import {CB} from '../internals/CB'
 
-import {Exit} from './Exit'
+import {Either} from './Either'
 import {FIO, UIO} from './FIO'
 
 /**
@@ -17,16 +17,10 @@ export class Await<E, A> {
   }
   private flag = false
   private readonly Q = mutable.DoublyLinkedList.of<[CB<E>, CB<A>]>()
-  private result: Exit<E, A> = Exit.pending
+  private result: Either<E, A> = Either.neither()
 
   public get get(): FIO<E, A> {
-    return this.getResult().chain(([status, result]) =>
-      status === Exit.Success
-        ? FIO.of(result)
-        : status === Exit.Failure
-        ? FIO.reject(result)
-        : this.wait()
-    ) as FIO<E, A>
+    return this.getResult().chain(e => e.fold(this.wait(), FIO.reject, FIO.of))
   }
 
   public get isSet(): UIO<boolean> {
@@ -40,32 +34,28 @@ export class Await<E, A> {
         : this.setFlag(true)
             .and(
               io
-                .chain(result => this.update(Exit.success(result)))
-                .catch(err => this.update(Exit.failure(err)))
+                .chain(result => this.update(Either.right(result)))
+                .catch(err => this.update(Either.left(err)))
             )
             .const(true)
     )
   }
 
-  private getResult(): UIO<Exit<E, A>> {
+  private getResult(): UIO<Either<E, A>> {
     return FIO.uio(() => this.result)
   }
 
   private setFlag(value: boolean): UIO<void> {
     return FIO.uio(() => void (this.flag = value))
   }
 
-  private update(result: Exit<E, A>): UIO<void> {
+  private update(result: Either<E, A>): UIO<void> {
     return FIO.uio(() => {
       this.result = result
 
       while (this.Q.length > 0) {
         const cb = this.Q.shift() as [CB<E>, CB<A>]
-        if (result[0] === Exit.Success) {
-          cb[1](result[1])
-        } else if (result[0] === Exit.Failure) {
-          cb[0](result[1])
-        }
+        result.fold(undefined, ...cb)
       }
     })
   }

src/main/Either.ts

@@ -0,0 +1,140 @@
+/* tslint:disable:prefer-function-over-method */
+
+/**
+ * Created by tushar on 07/09/19
+ */
+
+export abstract class Either<L1, R1> {
+  public static left<L>(left: L): Either<L, never> {
+    return new Left(left)
+  }
+  public static neither(): Either<never, never> {
+    return new Neither()
+  }
+  public static right<R>(right: R): Either<never, R> {
+    return new Right(right)
+  }
+
+  public abstract biChain<L2, R2>(
+    LL: (l: L1) => Either<L2, R2>,
+    RR: (r: R1) => Either<L2, R2>
+  ): Either<L2, R2>
+
+  public biMap<L2, R2>(LL: (l: L1) => L2, RR: (r: R1) => R2): Either<L2, R2> {
+    return this.mapL(LL).mapR(RR)
+  }
+
+  public chain<R2>(ab: (r: R1) => Either<L1, R2>): Either<L1, R2> {
+    return this.chainR(ab)
+  }
+  public chainL<L2>(ab: (l: L1) => Either<L2, R1>): Either<L2, R1> {
+    return this.biChain(ab, Either.right)
+  }
+  public chainR<R2>(ab: (r: R1) => Either<L1, R2>): Either<L1, R2> {
+    return this.biChain(Either.left, ab)
+  }
+
+  public abstract fold<S>(
+    seed: S,
+    LL: (l: L1, s: S) => S,
+    RR: (r: R1, s: S) => S
+  ): S
+
+  public abstract getLeftOrElse(left: L1): L1
+  public abstract getRightOrElse(right: R1): R1
+  public map<R2>(ab: (r: R1) => R2): Either<L1, R2> {
+    return this.mapR(ab)
+  }
+  public mapL<L2>(ab: (r: L1) => L2): Either<L2, R1> {
+    return this.chainL(r => Either.left(ab(r)))
+  }
+
+  public mapR<R2>(ab: (r: R1) => R2): Either<L1, R2> {
+    return this.chainR(r => Either.right(ab(r)))
+  }
+}
+
+class Left<L1> extends Either<L1, never> {
+  public readonly isLeft = true
+  public readonly isNeither = false
+  public readonly isRight = false
+
+  public constructor(public readonly left: L1) {
+    super()
+  }
+
+  public biChain<L2, R2>(
+    LL: (l: L1) => Either<L2, R2>,
+    RR: (r: never) => Either<L2, R2>
+  ): Either<L2, R2> {
+    return LL(this.left)
+  }
+
+  public fold<S>(S: S, LL: (l: L1, s: S) => S, RR: (r: never, s: S) => S): S {
+    return LL(this.left, S)
+  }
+
+  public getLeftOrElse(left: L1): L1 {
+    return this.left
+  }
+
+  public getRightOrElse(right: never): never {
+    return right
+  }
+}
+
+class Right<R1> extends Either<never, R1> {
+  public readonly isLeft = false
+  public readonly isNeither = false
+  public readonly isRight = true
+
+  public constructor(public readonly right: R1) {
+    super()
+  }
+
+  public biChain<L2, R2>(
+    LL: (l: never) => Either<L2, R2>,
+    RR: (r: R1) => Either<L2, R2>
+  ): Either<L2, R2> {
+    return RR(this.right)
+  }
+  public fold<S>(S: S, LL: (l: never, s: S) => S, RR: (r: R1, s: S) => S): S {
+    return RR(this.right, S)
+  }
+
+  public getLeftOrElse(left: never): never {
+    return left
+  }
+  public getRightOrElse(right: R1): R1 {
+    return this.right
+  }
+}
+
+class Neither extends Either<never, never> {
+  public readonly isLeft = false
+  public readonly isNeither = true
+  public readonly isRight = false
+
+  public biChain<L2, R2>(
+    LL: (l: never) => Either<L2, R2>,
+    RR: (r: never) => Either<L2, R2>
+  ): Either<L2, R2> {
+    return this
+  }
+
+  public fold<S>(
+    S: S,
+    LL: (l: never, s: S) => S,
+    RR: (r: never, s: S) => S
+  ): S {
+    return S
+  }
+
+  public getLeftOrElse(left: never): never {
+    return left
+  }
+
+  public getRightOrElse(right: never): never {
+    return right
+  }
+}

src/main/Exit.ts

@@ -8,16 +8,17 @@ import {ICancellable, IScheduler} from 'ts-scheduler'
 
 import {CB} from '../internals/CB'
 import {coordinate} from '../internals/Coordinate'
+import {Id} from '../internals/Id'
 import {IRuntime} from '../runtimes/IRuntime'
 
 import {Await} from './Await'
-import {Exit} from './Exit'
+import {Either} from './Either'
 import {Fiber} from './Fiber'
 import {Instruction, Tag} from './Instructions'
 import {Ref} from './Ref'
 
-const Id = <A>(_: A): A => _
-const ExitRef = <E = never, A = never>() => Ref.of<Exit<E, A>>(Exit.pending)
+const ExitRef = <E = never, A = never>() =>
+  Ref.of<Either<E, A>>(Either.neither())
 
 export type NoEnv = unknown
 
@@ -224,14 +225,10 @@ export class FIO<E1 = unknown, A1 = unknown, R1 = NoEnv> {
   }
 
   /**
-   * Creates an IO from [[Exit]]
+   * Creates an IO from [[Either]]
    */
-  public static fromExit<E, A>(exit: Exit<E, A>): FIO<E, A> {
-    return Exit.isSuccess(exit)
-      ? FIO.of(exit[1])
-      : Exit.isFailure(exit)
-      ? FIO.reject(exit[1])
-      : FIO.never()
+  public static fromExit<E, A>(exit: Either<E, A>): IO<E, A> {
+    return exit.fold<IO<E, A>>(FIO.never(), FIO.reject, FIO.of)
   }
 
   /**
@@ -541,8 +538,8 @@ export class FIO<E1 = unknown, A1 = unknown, R1 = NoEnv> {
    */
   public raceWith<E2, A2, R2>(
     that: FIO<E2, A2, R2>,
-    cb1: (exit: Exit<E1, A1>, fiber: Fiber<E2, A2>) => UIO<void>,
-    cb2: (exit: Exit<E2, A2>, fiber: Fiber<E1, A1>) => UIO<void>
+    cb1: (exit: Either<E1, A1>, fiber: Fiber<E2, A2>) => UIO<void>,
+    cb2: (exit: Either<E2, A2>, fiber: Fiber<E1, A1>) => UIO<void>
   ): FIO<never, void, R1 & R2> {
     return this.fork.zip(that.fork).chain(({0: f1, 1: f2}) => {
       const resume1 = f1.resumeAsync(exit => cb1(exit, f2))
@@ -553,10 +550,10 @@ export class FIO<E1 = unknown, A1 = unknown, R1 = NoEnv> {
   }
 
   /**
-   * Runs the [[FIO]] instance asynchronously and calls the callback passed with an [[Exit]] object.
+   * Runs the [[FIO]] instance asynchronously and calls the callback passed with an [[Either]] object.
    */
   public resumeAsync(
-    cb: (exit: Exit<E1, A1>) => UIO<void>
+    cb: (exit: Either<E1, A1>) => UIO<void>
   ): FIO<never, void, R1> {
     return this.fork.chain(_ => _.resumeAsync(cb))
   }

src/main/FIO.ts

@@ -2,7 +2,7 @@ import {ICancellable} from 'ts-scheduler'
 
 import {FIO, UIO} from '../main/FIO'
 
-import {Exit} from './Exit'
+import {Either} from './Either'
 
 /**
  * Fibers are data structures that provide you a handle to control the execution of its `IO`.
@@ -24,5 +24,5 @@ export abstract class Fiber<E, A> implements ICancellable {
   public cancel(): void {
     this.$abort()
   }
-  public abstract resumeAsync(cb: (exit: Exit<E, A>) => UIO<void>): UIO<void>
+  public abstract resumeAsync(cb: (exit: Either<E, A>) => UIO<void>): UIO<void>
 }