import { type AsymmetricMatcher } from './shared/predicates';
import type { MatcherResult } from './shared/types';
declare global {
    namespace jest {
        interface Matchers<R> {
            toEqualLeft(expected: unknown): R;
        }
    }
}
/**
 * Asserts that the left side of an `Either` equals an expected value or
 * asymmetric matcher.
 *
 * @typeParam L Type of the expected left value.
 *
 * @param expected Value or asymmetric matcher that should equal the left side.
 *
 * @example
 * ```typescript
 * import { left } from 'fp-ts/lib/Either'
 *
 * test('passes when left of Either equals a value', () => {
 *   const actual = left(Error('message'))
 *   expect(actual).toEqualLeft(Error('message'))
 * })
 *
 * test('passes when left of Either does not equal a value', () => {
 *   const actual = left(Error('unexpected'))
 *   expect(actual).not.toEqualLeft(Error('message'))
 * })
 * ```
 */
export declare function toEqualLeft<L>(actual: unknown, expected: L | AsymmetricMatcher): MatcherResult;