rivo/List/ExtendW.d.ts

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import type { List } from ".";
// @ts-ignore - Only used in doc comments
import type { Extend } from "./Extend";
// @ts-ignore - Only used in doc comments
import type ExtendFn from "./Extend";
// @ts-ignore - Only used in doc comments
import type { ExtendLeftW } from "./ExtendLeftW";
// @ts-ignore - Only used in doc comments
import type ExtendLeftWFn from "./ExtendLeftW";
import type { Args, GenericFn, GenericResolver } from "../HKT";

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

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

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