Add AsyncDoEither class

src/either.ts

@@ -176,3 +176,137 @@ export class DoEither<T extends Record<string, unknown>, E> {
     return new DoEither(right({}))
   }
 }
+
+/**
+ * A class for working with Either in a do-notation style with asynchronous computations
+ * @typeParam T - The type of the accumulated scope
+ * @typeParam E - The error type
+ */
+export class AsyncDoEither<T extends Record<string, unknown>, E> {
+  /**
+   * @param promise - The current Promise of an Either value
+   */
+  constructor(private readonly promise: Promise<Either<T, E>>) {}
+
+  /**
+   * Binds a new value to the scope synchronously
+   * @typeParam K - The key to bind to
+   * @typeParam A - The type of the value to bind
+   * @param key - The property name to bind to
+   * @param fa - The Either value to bind
+   * @returns A new AsyncDoEither instance with the extended scope
+   */
+  bind<K extends string, A>(
+    key: K,
+    fa: Either<A, E>,
+  ): AsyncDoEither<T & Record<K, A>, E> {
+    return this.bindL(key, () => fa)
+  }
+
+  /**
+   * Binds a new value to the scope asynchronously
+   * @typeParam K - The key to bind to
+   * @typeParam A - The type of the value to bind
+   * @param key - The property name to bind to
+   * @param f - Function returning Either or Promise of Either
+   * @returns A new AsyncDoEither instance with the extended scope
+   */
+  bindL<K extends string, A>(
+    key: K,
+    f: (scope: T) => Either<A, E> | Promise<Either<A, E>>,
+  ): AsyncDoEither<T & Record<K, A>, E> {
+    const newPromise = this.promise.then(async (currentEither) => {
+      if (isLeft(currentEither)) {
+        return currentEither as unknown as Either<T & Record<K, A>, E>
+      }
+
+      const scope = currentEither.right
+      try {
+        const nextEither = await f(scope)
+
+        if (isLeft(nextEither)) {
+          return nextEither as unknown as Either<T & Record<K, A>, E>
+        }
+
+        return right({
+          ...scope,
+          [key]: nextEither.right,
+        }) as Either<T & Record<K, A>, E>
+      } catch (err) {
+        return left(err as E) as Either<T & Record<K, A>, E>
+      }
+    })
+
+    return new AsyncDoEither(newPromise)
+  }
+
+  /**
+   * Returns the final result from the scope
+   * @typeParam B - The return type
+   * @param f - The function to transform the scope
+   * @returns A Promise of Either containing the result
+   */
+  return<B>(f: (scope: T) => B): Promise<Either<B, E>> {
+    return this.promise.then(either => {
+      if (isLeft(either)) {
+        return either as unknown as Either<B, E>
+      }
+      return right(f(either.right))
+    })
+  }
+
+  /**
+   * Returns the current scope
+   * @returns A Promise of the current Either scope
+   */
+  done(): Promise<Either<T, E>> {
+    return this.promise
+  }
+
+  /**
+   * Executes an effect without modifying the scope
+   * @param fa - The Either effect to execute
+   * @returns A new AsyncDoEither instance with the same scope
+   */
+  do(fa: Either<unknown, E>): AsyncDoEither<T, E> {
+    return this.doL(() => fa)
+  }
+
+  /**
+   * Executes an effect that depends on the current scope
+   * @param f - Function returning Either or Promise of Either
+   * @returns A new AsyncDoEither instance with the same scope
+   */
+  doL(f:
+    (scope: T) =>
+      | Either<unknown, E>
+      | Promise<Either<unknown, E>>): AsyncDoEither<T, E>
+  {
+    const newPromise = this.promise.then(async (currentEither) => {
+      if (isLeft(currentEither)) {
+        return currentEither
+      }
+
+      const scope = currentEither.right
+      try {
+        const effectEither = await f(scope)
+        if (isLeft(effectEither)) {
+          return effectEither as unknown as Either<T, E>
+        }
+        return currentEither
+      } catch (err) {
+        return left(err as E)
+      }
+    })
+
+    return new AsyncDoEither(newPromise)
+  }
+
+  /**
+   * Starts a new AsyncDoEither chain with an empty scope
+   * @returns A new AsyncDoEither instance with an empty scope
+   */
+  static start<E>(): AsyncDoEither<{}, E> {
+    return new AsyncDoEither(Promise.resolve(right({})))
+  }
+}