import type { Arg0, Fn } from "../HKT";
import type { AssertStr, IsNever } from "../helpers";

/**
 * Convert `undefined` to a string.
 *
 * Sig: `(u: undefined) => string`
 */
export type ToStr<U extends undefined> = AssertStr<IsNever<U> extends true ? never : "undefined">;

/**
 * [Fn] Convert `undefined` to a string.
 *
 * Sig: `(u: undefined) => string`
 */
export default interface ToStrFn extends Fn<[undefined], string> {
  def: () => ToStr<Arg0<this>>;
}