import { type Asyncerator } from '../asyncerator.ts';
/**
 * Calls the specified callback function for all the elements in a stream. The return value of the callback function
 * is the accumulated result, and is provided as an argument in the next call to the callback function.
 * Equivalent to the Javascript Array.reduce() method.
 *
 * @param reduceFunction The reduce method calls the reduceFunction function one time for each element in the stream.
 * @param initialValue If initialValue is specified, it is used as the previousValue to start the accumulation.
 * Otherwise, the initial previousValue will be undefined.
 */
export type ReduceFunction<Input, Output> = (previousValue: Output, currentValue: Input, currentIndex: number) => Output;
export default function <Input>(reduceFunction: ReduceFunction<Input, Input>, initialValue?: Input): (iterator: Asyncerator<Input>) => Promise<Input | undefined>;
export default function <Input, Output>(reduceFunction: ReduceFunction<Input, Output>, initialValue?: Output): (iterator: Asyncerator<Input>) => Promise<Output | undefined>;