import { BaseRetriever, BaseRetrieverInput } from "@langchain/core/retrievers";
import { Document } from "@langchain/core/documents";
export type BM25RetrieverOptions = {
    docs: Document[];
    k: number;
} & BaseRetrieverInput;
/**
 * A retriever that uses the BM25 algorithm to rank documents based on their
 * similarity to a query. It uses the "okapibm25" package for BM25 scoring.
 * The k parameter determines the number of documents to return for each query.
 */
export declare class BM25Retriever extends BaseRetriever {
    static lc_name(): string;
    lc_namespace: string[];
    static fromDocuments(documents: Document[], options: Omit<BM25RetrieverOptions, "docs">): BM25Retriever;
    docs: Document[];
    k: number;
    constructor(options: BM25RetrieverOptions);
    private preprocessFunc;
    _getRelevantDocuments(query: string): Promise<Document<Record<string, any>>[]>;
}