import { Accumulator } from '@johngw/stream-common/Function';
import { Flushable } from '@johngw/stream-common/Stream';
/**
 * Reduces chunks in to one accumulator. Once the stream is cancelled,
 * the accumulator will be queued.
 *
 * @group Transformers
 * @see {@link accumulate:function}
 * @example
 *
 * --a-------b-------c-----|
 *
 * reduce([], (acc, chunk) => [...acc, chunk])
 *
 * ------------------------[a,b,c]-|
 */
export declare function reduce<I, O>(acc: O, fn: Accumulator<I, O>, options?: Flushable): TransformStream<I, O>;