import * as p_di from "../../schema.js";
export type Option<T extends p_di.Value> = readonly [string, T];
/**
 * used to make the value T the context variable ('$')
 * given a tuple of a string and a value T,
 * the function takes the value T and calls back the callback ($)
 * notice that the string part is never used
 *
 * example:
 *
 * switch ($.state[0]) {
 *     case 'on': return p_.option($.state, ($) => $.value)
 *     case 'off': return p_.option($.state, ($) => null)
 *     default: return p_.exhaustive($.state[0])
 * }
 */
export declare function option<T extends p_di.Value, RT extends p_di.Value>(option: Option<T>, $c: ($: T) => RT): RT;
export declare function exhaustive<RT>(_x: never): RT;