example.ts

import {type Box, all, flat, map, nah, or, pipe, tap, yep} from './lib.js';

class HttpError extends Error {}
class ParseError extends Error {}

const req = (url: string): Box<Response, HttpError> =>
  fetch(url)
    .then(yep)
    .catch(() => nah(new HttpError('http error')));

const parse = <T>(res: Response): Box<T, ParseError> =>
  res
    .json()
    .then((json) => yep(json as T))
    .catch(() => nah(new ParseError('json parse error')));

const checkStatus = (res: Response) =>
  res.status >= 400 ? nah(new HttpError('status error')) : yep(res);

const getPokemon = (name: string) =>
  pipe(
    yep(`https://pokeapi.co/api/v2/pokemon/${name}`),
    flat(req),
    tap((res) =>
      console.log(`Requested ${name} with response status ${res.status}`),
    ),
    flat(checkStatus),
    flat(parse<{weight: number; name: string}>),
  );

const program = pipe(
  yep(['ditto', 'onix']),
  flat((names) => all(names.map(getPokemon))),
  map(([v, w]) =>
    v.weight < w.weight
      ? `${w.name} heavier then ${v.name}`
      : `${v.name} heavier then ${w.name}`,
  ),
  or((e) => yep(`recovered err: ${e.message}`)),
);

program.then(console.log);