import type { CustomOptions, CustomValidate } from "../custom/index.ts";
/**
 * Determines whether the input is a Promise.
 *
 * @param input The value being checked.
 * @param validate The validation function.
 * @returns `true` if the input is a File, `false` otherwise.
 */
export declare function isPromise<T extends Promise<any>>(input: unknown, validate?: CustomValidate<T>): input is T;
export type PromiseOptions<T extends Promise<any>> = Omit<CustomOptions<T>, "typecheck">;
/**
 * Verifies that the input is a Promise.
 *
 * @param input The value to check.
 * @param fallback The value to return if the input is not a File. Default is `null`.
 * @param options Customization options.
 * @returns The input if it is a File; the fallback otherwise.
 */
export declare function promise<T extends Promise<any>>(input: unknown, fallback: T, options?: PromiseOptions<T>): T;
export declare function promise<T extends Promise<any>>(input: unknown, fallback?: T | null | undefined, options?: PromiseOptions<T>): T | null;