import { int, nat } from "things";
import { GrammarSymbols } from "./grammar_symbols.js";
export declare class Rule {
    lhs: nat;
    rhs: int[];
    constructor(lhs: nat, rhs: int[]);
    asString(symbols: GrammarSymbols): string;
}
/** Nonterminals are > 0, terminals are < 0, 0 is the end of the input. */
export declare class Grammar {
    start: nat;
    rules: Rule[];
    constructor(start: nat, rules: Rule[]);
}
export declare function computeProductiveNonterminals(rules: (Rule | null)[]): Set<nat>;
export declare function removeUnproductiveNonterminals(rules: Rule[]): Rule[];