rivo/Option/Map.d.ts

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import type { None, Option, Some } from ".";
import type { Args, Call1, Fn1, GenericFn, GenericResolver, Param0, Return } from "../HKT";

/**
 * Apply a function to an {@link Option} value if it is {@link Some}, otherwise return {@link None}.
 *
 * Sig: `<T, U>(f: (x: T) => U, o: Option<T>) => Option<U>`
 */
export type Map<F extends Fn1, O extends Option<unknown>> =
  O extends Some<infer T extends Param0<F>> ? Some<Call1<F, T>> : None;

interface Resolver extends GenericResolver<[Fn1, Option<unknown>], Option<unknown>> {
  on1_: ([f]: Args<this>) => [[Option<Param0<typeof f>>], Option<Return<typeof f>>];
  on_1: ([, o]: Args<this>) => [
    [Fn1<typeof o extends Option<infer T> ? T : never>],
    Option<unknown>,
  ];
  on11: ([f, o]: Args<this>) => [[], Option<Return<typeof f>>];
}

/**
 * [Fn] Apply a function to an {@link Option} value if it is {@link Some}, otherwise return
 * {@link None}.
 *
 * Sig: `<T, U>(f: (x: T) => U, o: Option<T>) => Option<U>`
 */
export default interface MapFn extends GenericFn<Resolver> {
  def: ([f, o]: Args<this>) => Map<typeof f, typeof o>;
}