import type { FlatAsyncIterable, FlatIterable } from "../../types/iterable/flat-iterable";
import type { AnyIterable } from "../../types";
/**
 * Flattens an input iterable up to a specified depth.
 * Returns a new asynchronous iterable.
 *
 * @group Lazy helpers
 * @template T - The type of elements in the input iterable.
 * @template D - The depth of flattening.
 * @param depth - The depth of flattening, defaults to 1.
 * @returns A function that accepts an input iterable and returns a new asynchronous iterable.
 *
 * @example
 * ```ts
 * const input = [1, [2, 3], [4, [5]]];
 * const flatIterable = flat<number>(1)(input);
 *
 * (async () => {
 *   for await (const x of flatIterable) {
 *     console.log(x); // Logs 1, 2, 3, 4, [5]
 *   }
 * })();
 * ```
 */
export declare const flat: <T, D extends number = 1>(depth?: D | undefined) => (input: AnyIterable<T>) => FlatAsyncIterable<T, D>;
/**
 * Flattens an input sync iterable up to a specified depth.
 * Returns a new synchronous iterable.
 *
 * @group Lazy helpers
 * @template T - The type of elements in the input sync iterable.
 * @template D - The depth of flattening.
 * @param depth - The depth of flattening, defaults to 1.
 * @returns A function that accepts an input sync iterable and returns a new synchronous iterable.
 *
 * @example
 * ```ts
 * const input = [1, [2, 3], [4, [5]]];
 * const flatSyncIterable = flatSync<number>(1)(input);
 *
 * for (const x of flatSyncIterable) {
 *   console.log(x); // Logs 1, 2, 3, 4, [5]
 * }
 * ```
 *
 * @remarks
 * Available as `flat` when imported from `peter-piper/sync`.
 */
export declare const flatSync: <T, D extends number = 1>(depth?: D | undefined) => (input: Iterable<T>) => FlatIterable<T, D>;