Function optionErr

optionErr<E, T>(res: Result.Result<E, T>): Option.Option<E>
Takes the error value as an optional if the result is an Err, otherwise returns None.
Type Parameters
- E
- T
Parameters
- res: Result.Result<E, T>
  The source result.
Returns Option.Option<E>
The error value if exists.

Examples
Example
```
expect(optionErr(ok(2))).toStrictEqual(none());
expect(optionErr(err("nothing left"))).toStrictEqual(some("nothing left"));
```
- Defined in src/result.ts:555