/**
 * @license
 * Copyright 2020-2023 Observable, Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any purpose
 * with or without fee is hereby granted, provided that the above copyright notice
 * and this permission notice appear in all copies.
 */
export declare function arrowPath(x1: number, y1: number, x2: number, y2: number, insetStart: number, insetEnd: number, headAngle: number, headLength: number, bend: number, strokeWidth: number, sweep: SweepFunc): string | null;
export declare function constant<T>(x: T): () => T;
export type SweepFunc = (x1: number, y1: number, x2: number, y2: number) => number;
export declare function keyword(input: string, name: string, allowed: string[]): string;
export type SweepOption = 1 | 0 | -1 | '+x' | '-x' | '+y' | '-y' | SweepFunc;
export declare function maybeSweep(sweep?: SweepOption): SweepFunc | undefined;