Introduction

In stream processing, a Sink is a construct designed to consume elements generated by a Stream.

     ┌─── Type of the result produced by the Sink
     |  ┌─── Type of elements consumed by the Sink
     |  |   ┌─── Type of any leftover elements
     │  |   |  ┌─── Type of possible errors
     │  │   |  |  ┌─── Type of required dependencies
     ▼  ▼   ▼  ▼  ▼
Sink<A, In, L, E, R>

Here’s an overview of what a Sink does:

It consumes a varying number of In elements, which may include zero, one, or multiple elements.
It can encounter errors of type E during processing.
It produces a result of type A once processing completes.
It can also return a remainder of type L, representing any leftover elements.

To process a stream using a Sink, you can pass it directly to the Stream.run function:

Example (Using a Sink to Collect Stream Elements)

1
import { import Stream
Stream, import Sink
Sink, import Effect
Effect } from "effect"
2

3
//      ┌─── Stream<number, never, never>
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//      ▼
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const const stream: Stream.Stream<number, never, never>
stream = import Stream
Stream.const make: <[number, number, number]>(as_0: number, as_1: number, as_2: number) => Stream.Stream<number, never, never>Creates a stream from an sequence of values.
make(1, 2, 3)
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// Create a sink to take the first 2 elements of the stream
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//
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//      ┌─── Sink<Chunk<number>, number, number, never, never>
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//      ▼
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const const sink: Sink.Sink<Chunk<number>, number, number, never, never>
sink = import Sink
Sink.const take: <number>(n: number) => Sink.Sink<Chunk<number>, number, number, never, never>A sink that takes the specified number of values.
take<number>(2)
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// Run the stream through the sink to collect the elements
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//
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//      ┌─── Effect<number, never, never>
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//      ▼
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const const sum: Effect.Effect<Chunk<number>, never, never>
sum = import Stream
Stream.const run: <number, never, never, Chunk<number>, never, never>(self: Stream.Stream<number, never, never>, sink: Sink.Sink<Chunk<number>, number, unknown, never, never>) => Effect.Effect<...> (+1 overload)Runs the sink on the stream to produce either the sink's result or an error.
run(const stream: Stream.Stream<number, never, never>
stream, const sink: Sink.Sink<Chunk<number>, number, number, never, never>
sink)
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import Effect
Effect.const runPromise: <Chunk<number>, never>(effect: Effect.Effect<Chunk<number>, never, never>, options?: {
    readonly signal?: AbortSignal;
} | undefined) => Promise<Chunk<number>>Executes an effect and returns a `Promise` that resolves with the result.

Use `runPromise` when working with asynchronous effects and you need to integrate with code that uses Promises.
If the effect fails, the returned Promise will be rejected with the error.
runPromise(const sum: Effect.Effect<Chunk<number>, never, never>
sum).(method) Promise<Chunk<number>>.then<void, never>(onfulfilled?: ((value: Chunk<number>) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<never>) | null | undefined): Promise<...>Attaches callbacks for the resolution and/or rejection of the Promise.
then(namespace console
var console: ConsoleThe `console` module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.

The module exports two specific components:

* A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream.
* A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and
[`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module.

_**Warning**_: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for
more information.

Example using the global `console`:

```js
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
```

Example using the `Console` class:

```js
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
```
console.(method) Console.log(message?: any, ...optionalParams: any[]): voidPrints to `stdout` with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html)
(the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)).

```js
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
```

See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.
log)
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/*
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Output:
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{ _id: 'Chunk', values: [ 1, 2 ] }
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*/

The type of sink is as follows:

       ┌─── result
       |              ┌─── consumed elements
       |              |       ┌─── leftover elements
       │              |       |       ┌─── no errors
       │              │       |       |      ┌─── no dependencies
       ▼              ▼       ▼       ▼      ▼
Sink<Chunk<number>, number, number, never, never>

Here’s the breakdown:

Chunk<number>: The final result produced by the sink after processing elements (in this case, a Chunk of numbers).
number (first occurrence): The type of elements that the sink will consume from the stream.
number (second occurrence): The type of leftover elements, if any, that are not consumed.
never (first occurrence): Indicates that this sink does not produce any errors.
never (second occurrence): Shows that no dependencies are required to operate this sink.