interface Matcher<Input> {
    (input: Input): boolean;
}
export interface ErrorContentFunction<Input> {
    (input: Input): string;
}
export declare type ErrorContent<Input> = string | ErrorContentFunction<Input>;
interface Options {
    skipOnEmpty?: boolean;
}
/**
 * A factory for creating reusable validation functions.
 *
 * ```tsx
 *  const isAColor = validator((input) => ['red', 'blue', 'green', 'yellow'].includes(input));
 *
 *  // the returned function takes an error string or a function to generate errors
 *  const colorField = useField({
 *    value: 'green',
 *    validates: isAColor((input) => `${input} is not a color`);
 *  })
 * ```
 *
 * By default validators will return true automatically if the value is empty (`null`, `undefined` or `''`). You can circumvent this by using the `skipOnEmpty` option.
 *
 * ```tsx
 *  const isAColor = validator(
 *    (input) => ['red', 'blue', 'green', 'yellow'].includes(input),
 *    {skipOnEmpty: false},
 *  );
 * ```
 *
 * @param matcher - a function that takes in an input and returns `true` if the value is valid, or `false` if it is not.
 * @param options - an optional configuration object.
 */
export declare function validator<Input = string>(matcher: Matcher<Input>, { skipOnEmpty }?: Options): (errorContent: ErrorContent<Input>) => (input: Input) => string | undefined;
export {};