/// <reference types="node" />
import * as stream from "stream";
export declare class ReduceTransform<TState = any, TEvent = any> extends stream.Transform {
    private readonly fn;
    private state;
    constructor(fn: (previous: TState, event: TEvent) => TState, initialState: TState);
    constructor(fn: (state?: TState, event?: TEvent) => TState, initialState?: TState);
    _transform(chunk: any, encoding: string, callback: (error?: Error, data?: any) => void): void;
}