rivo/List/ToUnion.d.ts

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

/**
 * Convert a {@link List} to a union type.
 *
 * Sig: `<T>(xs: List<T>) => T`
 */
export type ToUnion<TS extends List> = TS[number];

interface Resolver extends GenericResolver<[List], unknown> {
  on1: ([xs]: Args<this>) => [[], (typeof xs)[number]];
}

/**
 * [Fn] Convert a {@link List} to a union type.
 *
 * Sig: `<T>(xs: List<T>) => T`
 */
export default interface ToUnionFn extends GenericFn<Resolver> {
  def: ([xs]: Args<this>) => ToUnion<typeof xs>;
}