export declare const BOOMERANG_RETURN: unique symbol;
/**
 * Iterate over an array and return when a certain point is met
 *  - Asynchronously iterate over an array of items until the
 *  return symbol is returned, which causes the boomerang to
 *  walk backwards over the list again
 */
export declare function boomerang<B>(arr: Array<B>, cb: (item: B, index: number, backwards?: boolean) => Promise<void | Symbol>): Promise<void>;