import type { Awaitable } from "./Awaitable";
type Reducer<S, T> = (state: S, x: T, i: number) => Awaitable<S>;
type ReducerWithUndefinedInitialState<T> = (state: T | undefined, x: T, i: number) => Awaitable<T>;
/** return undefined to skip emit */
export declare const reduces: {
    <T>(fn: ReducerWithUndefinedInitialState<T>): TransformStream<T, T>;
    <T>(fn: Reducer<T, T>, initialState: T): TransformStream<T, T>;
    <T, S>(fn: Reducer<S, T>): TransformStream<T, S>;
    <T, S>(fn: Reducer<S, T>, initialState: S): TransformStream<T, S>;
};
export {};