import type { ToIntersection } from "./ToIntersection";
import type { Arg0, Fn } from "../HKT";

/**
 * Check whether a type is a union type.
 *
 * Sig: `(x: unknown) => boolean`
 */
export type IsUnion<U> = [U] extends [ToIntersection<U>] ? false : true;

/**
 * [Fn] Check whether a type is a union type.
 *
 * Sig: `(x: unknown) => boolean`
 */
export interface IsUnionFn extends Fn<[unknown], boolean> {
  def: () => IsUnion<Arg0<this>>;
}