Function effectify

src/effected.ts:2515–2544

(promise: Promise<T>)

 * ```
 */
export function effectify<T>(promise: Promise<T>): Effected<never, T> {
  return effected(() => {
    let state = 0;
    return {
      next: (...args) => {
        switch (state) {
          case 0:
            state++;
            return {
              done: false,
              value: {
                _effectAsync: true,
                onComplete: (
                  ...args: [onComplete: (value: T) => void, onThrow?: (value: unknown) => void]
                ) => promise.then(...args),
              } as never,
            };
          case 1:
            state++;
            return {
              done: true,
              ...(args.length > 0 ? { value: args[0] } : {}),
            } as IteratorReturnResult<T>;
          default:
            return { done: true } as IteratorReturnResult<T>;
        }
      },
    };
  });
}

/**
 * Run an effected program synchronously and return its result.