import type { Args, GenericFn, GenericResolver } from "../HKT";

/**
 * Get the element at index 0 of a tuple.
 *
 * Sig: `<TS extends readonly [unknown, ...unknown[]]>(xs: TS) => TS[0]`
 */
export type _0<TS extends readonly unknown[]> = TS[0];

interface Resolver extends GenericResolver<[readonly [unknown, ...unknown[]]], unknown> {
  on1: ([xs]: Args<this>) => [[], (typeof xs)[0]];
}

/**
 * [Fn] Get the element at index 0 of a tuple.
 *
 * Sig: `<TS extends readonly [unknown, ...unknown[]]>(xs: TS) => TS[0]`
 */
export default interface _0Fn extends GenericFn<Resolver> {
  def: ([xs]: Args<this>) => _0<typeof xs>;
}