rivo/List/ConcatW.d.ts

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import type { List } from ".";
// @ts-ignore - `Concat` is only used in doc comments
import type { Concat } from "./Concat";
import type { Args, GenericFn, GenericResolver } from "../HKT";

/**
 * Less strict version of {@link Concat}.The **W** suffix (short for **W**idening) means that both
 * {@link List}s can hold different types.
 *
 * Sig: `<T, U>(xs: List<T>, ys: List<U>) => List<T | U>`
 */
export type ConcatW<TS extends List, US extends List> =
  TS extends unknown[] ? [...TS, ...US] : readonly [...TS, ...US];

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

/**
 * [Fn] Less strict version of {@link Concat}. The **W** suffix (short for **W**idening) means that
 * both {@link List}s can hold different types.
 *
 * Sig: `<T, U>(xs: List<T>, ys: List<U>) => List<T | U>`
 */
export default interface ConcatWFn extends GenericFn<Resolver> {
  def: ([xs, ys]: Args<this>) => ConcatW<typeof xs, typeof ys>;
}