rivo/List/Contains.d.ts

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import type { List } from ".";
import type { Args, GenericFn, GenericResolver } from "../HKT";
import type { Broaden, Eq } from "../helpers";

/**
 * Check if a {@link List} contains a specific element.
 *
 * Sig: `<T>(x: T, xs: List<T>) => boolean`
 */
export type Contains<T extends TS[number], TS extends List> =
  unknown extends T ? boolean
  : number extends TS["length"] ?
    Eq<T, TS[number]> extends true ?
      true
    : boolean
  : TS extends readonly [infer Head, ...infer Tail] ?
    Eq<T, Head> extends true ? true
    : T extends Head ?
      Contains<T, Tail> extends true ?
        true
      : boolean
    : Contains<T, Tail>
  : false;

interface Resolver extends GenericResolver<[unknown, List], boolean> {
  on1_: ([x]: Args<this>) => [[List<Broaden<typeof x>>], boolean];
  on_1: ([, xs]: Args<this>) => [[Broaden<(typeof xs)[number]>], boolean];
  on11: ([x, xs]: Args<this>) => [[], boolean];
}

/**
 * [Fn] Check if a {@link List} contains a specific element.
 *
 * Sig: `<T>(x: T, xs: List<T>) => boolean`
 */
export default interface ContainsFn extends GenericFn<Resolver> {
  def: ([x, xs]: Args<this>) => Contains<typeof x, typeof xs>;
}