Function filter

filter<V>(predicate: (item: V) => Awaitable<boolean | undefined>): Task<V>
Creates a task retaining only the items matching a predicate.

Items are tested lazily, one at a time, and emitted in source order.
Type Parameters
- V
  The type of items in the feed
Parameters
- predicate: (item: V) => Awaitable<boolean | undefined>
  The function testing each item; an undefined result is treated as false and the item is discarded
Returns Task<V>
A task yielding the items matching predicate
Example
```
await pipe(
  (items(1, 2, 3, 4, 5))
  (filter(n => n%2 === 0))
  (toArray())
);  // [2, 4]
```
- Defined in tasks/filter.ts:43