/**
 * Aggregates a sequence into a single result by iteratively combining elements.
 *
 * @typeParam T - Element type produced by the source iterable.
 * @typeParam TOut - Accumulator result type when a distinct seed is supplied.
 * @typeParam TT - Effective accumulator type when `seed` is optional.
 * @param src - Source iterable to be reduced.
 * @param aggFunc - Combiner invoked with the previous accumulator, current element, and current index.
 * @param seed - Optional initial accumulator; falls back to the first element when omitted.
 * @returns The final accumulator produced after the reducer runs over the entire sequence.
 * @throws {Error} If `seed` is omitted and the source iterable is empty.
 * @example
 * ```ts
 * const total = _reduce([1, 2, 3], (prev, curr) => prev + curr);
 * console.log(total); // 6
 *
 * const product = _reduce([1, 2, 3], (prev, curr) => prev * curr, 1);
 * console.log(product); // 6
 * ```
 */
export declare function _reduce<T, TOut>(src: Iterable<T>, aggFunc: (prev: TOut, curr: T, idx: number) => TOut, seed: TOut): TOut;
export declare function _reduce<T>(src: Iterable<T>, aggFunc: (prev: T, curr: T, idx: number) => T): T;
/**
 * Curried version of {@link _reduce}.
 */
export declare function reduce<T, TOut>(aggFunc: (prev: TOut, curr: T, idx: number) => TOut, seed: TOut): (source: Iterable<T>) => TOut;
export declare function reduce<T>(aggFunc: (prev: T, curr: T, idx: number) => T): (source: Iterable<T>) => T;