import { QuotedToken, Token } from '../tokens';
import type { Context } from '../context';
export declare class Expression {
    readonly postfix: Token[];
    constructor(tokens: Iterable<Token>);
    evaluate(ctx: Context, lenient?: boolean): Generator<unknown, unknown, unknown>;
    valid(): boolean;
}
/**
 * Evaluate `token`, preserving Drops.
 * Operators use this so `Comparable` drops (`empty`, `nil`, `blank`) and custom drops
 * are compared as drops rather than as their `valueOf()` result.
 */
export declare function evalToken(token: Token | undefined, ctx: Context, lenient?: boolean): IterableIterator<unknown>;
/**
 * Evaluate `token` to the value filters and tags consume.
 * Awaits a promise returned by `Drop.valueOf()`.
 */
export declare function evalTokenValue(token: Token | undefined, ctx: Context, lenient?: boolean): IterableIterator<unknown>;
export declare function evalQuotedToken(token: QuotedToken): string;