rivo
Version:
🤖 The ultimate library you need for composable type-level programming in TypeScript, powered by HKT.
25 lines (21 loc) • 693 B
TypeScript
import type { List } from ".";
import type { Args, GenericFn, GenericResolver } from "../HKT";
import type { None, Option, Some } from "../Option";
/**
* Get the first element in a {@link List}.
*
* Sig: `<T>(xs: List<T>) => Option<T>`
*/
export type Head<TS extends List> =
TS extends readonly [infer Head, ...unknown[]] ? Some<Head> : None;
interface Resolver extends GenericResolver<[List], Option<unknown>> {
on1: ([xs]: Args<this>) => [[], Option<(typeof xs)[number]>];
}
/**
* Get the first element in a {@link List}.
*
* Sig: `<T>(xs: List<T>) => Option<T>`
*/
export default interface HeadFn extends GenericFn<Resolver> {
def: ([xs]: Args<this>) => Head<typeof xs>;
}