coproduto

const reverse = (array) =>
  array.reduce((acc, elem) => [elem].concat(acc), []);

const map = (array, fun) =>
  reverse(array.reduce((acc, elem) => [fun(elem)].concat(acc), []));

const filter = (array, pred) =>
  reverse(array.reduce((acc, elem) => pred(elem) ? [elem].concat(acc) : acc, []));