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@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
2

3
//      ┌─── Stream<number, never, never>
4
//      ▼
5
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.
@example 
import { Effect, Stream } from "effect"

const stream = Stream.make(1, 2, 3)

// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 1, 2, 3 ] }
@since ― 2.0.0
make(1, 2, 3)
6

7
// Create a sink to take the first 2 elements of the stream
8
//
9
//      ┌─── Sink<Chunk<number>, number, number, never, never>
10
//      ▼
11
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.
@since ― 2.0.0
take<number>(2)
12

13
// Run the stream through the sink to collect the elements
14
//
15
//      ┌─── Effect<number, never, never>
16
//      ▼
17
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.
@since ― 2.0.0
run(
const stream: Stream.Stream<number, never, never>
stream, 
const sink: Sink.Sink<Chunk<number>, number, number, never, never>
sink)
18

19
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
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 the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example 
// Title: Running a Successful Effect as a Promise
import { Effect } from "effect"

Effect.runPromise(Effect.succeed(1)).then(console.log)
// Output: 1
@example 
//Example: Handling a Failing Effect as a Rejected Promise
import { Effect } from "effect"
Effect.runPromise(Effect.fail("my error")).catch(console.error)
// Output:
// (FiberFailure) Error: my error
@since ― 2.0.0
runPromise(
const sum: Effect.Effect<Chunk<number>, never, never>
sum).
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.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
var console: Console
The 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 and
process.stderr. 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 for
more information.
Example using the global console:
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:
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
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
Prints 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)
(the arguments are all passed to util.format()).
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() for more information.
@since ― v0.1.100
log)
20
/*
21
Output:
22
{ _id: 'Chunk', values: [ 1, 2 ] }
23
*/

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.