isLeft
import { isLeft } from "https://github.gh-proxy.cn/raw.githubusercontent.com/baetheus/fun/main/these.ts";Check if a These is a Left (complete failure).
@example
import { isLeft, left, right, both } from "./these.ts";
console.log(isLeft(left("Error"))); // true
console.log(isLeft(right(42))); // false
console.log(isLeft(both("Warning", 42))); // false