Function filter

filter<T>(
predicate: (t: T) => boolean,
): (opt: Option.Option<T>) => Option.Option<T>
Returns Some only if opt is a Some and its value satisfies predicate, otherwise returns None.
Type Parameters
- T
Parameters
- predicate: (t: T) => boolean
  The predicate to filter a value of opt.
Returns (opt: Option.Option<T>) => Option.Option<T>
The filtered optional.

Examples
Example
```
const isEven = filter((x: number) => x % 2 == 0);

expect(isEven(none())).toStrictEqual(none());
expect(isEven(some(3))).toStrictEqual(none());
expect(isEven(some(4))).toStrictEqual(some(4));
```
- Defined in src/option.ts:452