method R.isErrimport { R } from "https://deno.land/x/ahh@v0.10.3/src/result/mod.ts"; isErr<T, E extends Error>(res: Result<T, E>): res is Err<E>Returns whether res is an Err. ExamplesExample 1 import { R } from "./mod.ts"; console.log(R.isErr(1)); // false console.log(R.isErr(Error())); // true Type ParametersTE extends ErrorParametersres: Result<T, E>Returnsres is Err<E>