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Creating Streams

In this section, we’ll explore various methods for creating Effect Streams. These methods will help you generate streams tailored to your needs.

You can create a pure stream by using the Stream.make constructor. This constructor accepts a variable list of values as its arguments.

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
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 ] }

@since2.0.0

make
(1, 2, 3)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

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.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
)).
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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 1, 2, 3 ] }

Sometimes, you may require a stream that doesn’t produce any values. In such cases, you can use Stream.empty. This constructor creates a stream that remains empty.

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
const
const stream: Stream.Stream<never, never, never>
stream
=
import Stream
Stream
.
const empty: Stream.Stream<never, never, never>

The empty stream.

@example

import { Effect, Stream } from "effect"
const stream = Stream.empty
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [] }

@since2.0.0

empty
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const runPromise: <Chunk<never>, never>(effect: Effect.Effect<Chunk<never>, never, never>, options?: {
readonly signal?: AbortSignal;
} | undefined) => Promise<Chunk<never>>

Executes an effect and returns the result as a Promise.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <never, never, never>(self: Stream.Stream<never, never, never>) => Effect.Effect<Chunk<never>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<never, never, never>
stream
)).
Promise<Chunk<never>>.then<void, never>(onfulfilled?: ((value: Chunk<never>) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<never>) | null | undefined): Promise<...>

Attaches callbacks for the resolution and/or rejection of the Promise.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [] }

If you need a stream that contains a single void value, you can use Stream.void. This constructor is handy when you want to represent a stream with a single event or signal.

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
const
const stream: Stream.Stream<void, never, never>
stream
=
import Stream
Stream
.
const void: Stream.Stream<void, never, never>
export void

A stream that contains a single void value.

@example

import { Effect, Stream } from "effect"
const stream = Stream.void
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ undefined ] }

@since2.0.0

void
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const runPromise: <Chunk<void>, never>(effect: Effect.Effect<Chunk<void>, never, never>, options?: {
readonly signal?: AbortSignal;
} | undefined) => Promise<Chunk<void>>

Executes an effect and returns the result as a Promise.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <void, never, never>(self: Stream.Stream<void, never, never>) => Effect.Effect<Chunk<void>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<void, never, never>
stream
)).
Promise<Chunk<void>>.then<void, never>(onfulfilled?: ((value: Chunk<void>) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<never>) | null | undefined): Promise<...>

Attaches callbacks for the resolution and/or rejection of the Promise.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ undefined ] }

To create a stream of integers within a specified range [min, max] (including both endpoints, min and max), you can use Stream.range. This is particularly useful for generating a stream of sequential numbers.

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
// Creating a stream of numbers from 1 to 5
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
const range: (min: number, max: number, chunkSize?: number) => Stream.Stream<number>

Constructs a stream from a range of integers, including both endpoints.

@example

import { Effect, Stream } from "effect"
// A Stream with a range of numbers from 1 to 5
const stream = Stream.range(1, 5)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 1, 2, 3, 4, 5 ] }

@since2.0.0

range
(1, 5)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

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.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
)).
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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 1, 2, 3, 4, 5 ] }

With Stream.iterate, you can generate a stream by applying a function iteratively to an initial value. The initial value becomes the first element produced by the stream, followed by subsequent values produced by f(init), f(f(init)), and so on.

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
// Creating a stream of incrementing numbers
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
const iterate: <number>(value: number, next: (value: number) => number) => Stream.Stream<number, never, never>

The infinite stream of iterative function application: a, f(a), f(f(a)), f(f(f(a))), ...

@example

import { Effect, Stream } from "effect"
// An infinite Stream of numbers starting from 1 and incrementing
const stream = Stream.iterate(1, (n) => n + 1)
// Effect.runPromise(Stream.runCollect(stream.pipe(Stream.take(10)))).then(console.log)
// { _id: 'Chunk', values: [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] }

@since2.0.0

iterate
(1, (
n: number
n
) =>
n: number
n
+ 1) // Produces 1, 2, 3, ...
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

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.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
.
Pipeable.pipe<Stream.Stream<number, never, never>, Stream.Stream<number, never, never>>(this: Stream.Stream<...>, ab: (_: Stream.Stream<number, never, never>) => Stream.Stream<number, never, never>): Stream.Stream<...> (+21 overloads)
pipe
(
import Stream
Stream
.
const take: (n: number) => <A, E, R>(self: Stream.Stream<A, E, R>) => Stream.Stream<A, E, R> (+1 overload)

Takes the specified number of elements from this stream.

@example

import { Effect, Stream } from "effect"
const stream = Stream.take(Stream.iterate(0, (n) => n + 1), 5)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 0, 1, 2, 3, 4 ] }

@since2.0.0

take
(5)))).
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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 1, 2, 3, 4, 5 ] }

Stream.scoped is used to create a single-valued stream from a scoped resource. It can be handy when dealing with resources that require explicit acquisition, usage, and release.

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
,
import Console
Console
} from "effect"
// Creating a single-valued stream from a scoped resource
const
const stream: Stream.Stream<void, never, never>
stream
=
import Stream
Stream
.
const scoped: <void, never, never>(effect: Effect.Effect<void, never, never>) => Stream.Stream<void, never, never>

Creates a single-valued stream from a scoped resource.

@example

import { Console, Effect, Stream } from "effect"
// Creating a single-valued stream from a scoped resource
const stream = Stream.scoped(
Effect.acquireRelease(
Console.log("acquire"),
() => Console.log("release")
)
).pipe(
Stream.flatMap(() => Console.log("use"))
)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// acquire
// use
// release
// { _id: 'Chunk', values: [ undefined ] }

@since2.0.0

scoped
(
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const acquireUseRelease: <void, never, never, void, never, never, void, never>(acquire: Effect.Effect<void, never, never>, use: (a: void) => Effect.Effect<void, never, never>, release: (a: void, exit: Exit<void, never>) => Effect.Effect<...>) => Effect.Effect<...> (+1 overload)

Creates a scoped resource and automatically handles the use effect during the scope.

Details

This function is similar to

acquireRelease

, but it introduces an additional use effect. This allows you to automatically execute the use effect while the resource is acquired, and it also ensures that the release effect is performed when the scope is closed.

The acquire effect is used to obtain the resource, the use effect operates while the resource is in use, and the release effect cleans up the resource when the scope ends.

@example

// Title: Automatically Managing Resource Lifetime
import { Effect, Console } from "effect"
// Define an interface for a resource
interface MyResource {
readonly contents: string
readonly close: () => Promise<void>
}
// Simulate resource acquisition
const getMyResource = (): Promise<MyResource> =>
Promise.resolve({
contents: "lorem ipsum",
close: () =>
new Promise((resolve) => {
console.log("Resource released")
resolve()
})
})
// Define how the resource is acquired
const acquire = Effect.tryPromise({
try: () =>
getMyResource().then((res) => {
console.log("Resource acquired")
return res
}),
catch: () => new Error("getMyResourceError")
})
// Define how the resource is released
const release = (res: MyResource) => Effect.promise(() => res.close())
const use = (res: MyResource) => Console.log(`content is ${res.contents}`)
// ┌─── Effect<void, Error, never>
// ▼
const program = Effect.acquireUseRelease(acquire, use, release)
// Effect.runPromise(program)
// Output:
// Resource acquired
// content is lorem ipsum
// Resource released

@since2.0.0

acquireUseRelease
(
import Console
Console
.
const log: (...args: ReadonlyArray<any>) => Effect.Effect<void>

@since2.0.0

log
("acquire"),
() =>
import Console
Console
.
const log: (...args: ReadonlyArray<any>) => Effect.Effect<void>

@since2.0.0

log
("use"),
() =>
import Console
Console
.
const log: (...args: ReadonlyArray<any>) => Effect.Effect<void>

@since2.0.0

log
("release")
)
)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const runPromise: <Chunk<void>, never>(effect: Effect.Effect<Chunk<void>, never, never>, options?: {
readonly signal?: AbortSignal;
} | undefined) => Promise<Chunk<void>>

Executes an effect and returns the result as a Promise.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <void, never, never>(self: Stream.Stream<void, never, never>) => Effect.Effect<Chunk<void>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<void, never, never>
stream
)).
Promise<Chunk<void>>.then<void, never>(onfulfilled?: ((value: Chunk<void>) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<never>) | null | undefined): Promise<...>

Attaches callbacks for the resolution and/or rejection of the Promise.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

console
.
globalThis.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.

@sincev0.1.100

log
)
/*
Output:
acquire
use
release
{ _id: 'Chunk', values: [ undefined ] }
*/

Much like the Effect data type, you can generate a Stream using the fail and succeed functions:

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
// Creating a stream that can emit errors
const
const streamWithError: Stream.Stream<never, string, never>
streamWithError
:
import Stream
Stream
.
interface Stream<out A, out E = never, out R = never>

A Stream<A, E, R> is a description of a program that, when evaluated, may emit zero or more values of type A, may fail with errors of type E, and uses an context of type R. One way to think of Stream is as a Effect program that could emit multiple values.

Stream is a purely functional pull based stream. Pull based streams offer inherent laziness and backpressure, relieving users of the need to manage buffers between operators. As an optimization, Stream does not emit single values, but rather an array of values. This allows the cost of effect evaluation to be amortized.

Stream forms a monad on its A type parameter, and has error management facilities for its E type parameter, modeled similarly to Effect (with some adjustments for the multiple-valued nature of Stream). These aspects allow for rich and expressive composition of streams.

@since2.0.0

@since2.0.0

Stream
<never, string> =
import Stream
Stream
.
const fail: <string>(error: string) => Stream.Stream<never, string, never>

Terminates with the specified error.

@example

import { Effect, Stream } from "effect"
const stream = Stream.fail("Uh oh!")
Effect.runPromiseExit(Stream.runCollect(stream)).then(console.log)
// {
// _id: 'Exit',
// _tag: 'Failure',
// cause: { _id: 'Cause', _tag: 'Fail', failure: 'Uh oh!' }
// }

@since2.0.0

fail
("Uh oh!")
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const runPromise: <Chunk<never>, string>(effect: Effect.Effect<Chunk<never>, string, never>, options?: {
readonly signal?: AbortSignal;
} | undefined) => Promise<Chunk<never>>

Executes an effect and returns the result as a Promise.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <never, string, never>(self: Stream.Stream<never, string, never>) => Effect.Effect<Chunk<never>, string, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const streamWithError: Stream.Stream<never, string, never>
streamWithError
))
// throws Error: Uh oh!
// Creating a stream that emits a numeric value
const
const streamWithNumber: Stream.Stream<number, never, never>
streamWithNumber
:
import Stream
Stream
.
interface Stream<out A, out E = never, out R = never>

A Stream<A, E, R> is a description of a program that, when evaluated, may emit zero or more values of type A, may fail with errors of type E, and uses an context of type R. One way to think of Stream is as a Effect program that could emit multiple values.

Stream is a purely functional pull based stream. Pull based streams offer inherent laziness and backpressure, relieving users of the need to manage buffers between operators. As an optimization, Stream does not emit single values, but rather an array of values. This allows the cost of effect evaluation to be amortized.

Stream forms a monad on its A type parameter, and has error management facilities for its E type parameter, modeled similarly to Effect (with some adjustments for the multiple-valued nature of Stream). These aspects allow for rich and expressive composition of streams.

@since2.0.0

@since2.0.0

Stream
<number> =
import Stream
Stream
.
const succeed: <number>(value: number) => Stream.Stream<number, never, never>

Creates a single-valued pure stream.

@example

import { Effect, Stream } from "effect"
// A Stream with a single number
const stream = Stream.succeed(3)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 3 ] }

@since2.0.0

succeed
(5)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

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.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const streamWithNumber: Stream.Stream<number, never, never>
streamWithNumber
)).
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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 5 ] }

You can construct a stream from a Chunk like this:

import {
import Stream
Stream
,
import Chunk
Chunk
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
// Creating a stream with values from a single Chunk
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
const fromChunk: <number>(chunk: Chunk.Chunk<number>) => Stream.Stream<number, never, never>

Creates a stream from a Chunk of values.

@example

import { Chunk, Effect, Stream } from "effect"
// Creating a stream with values from a single Chunk
const stream = Stream.fromChunk(Chunk.make(1, 2, 3))
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 1, 2, 3 ] }

@since2.0.0

fromChunk
(
import Chunk
Chunk
.
const make: <[number, number, number]>(as_0: number, as_1: number, as_2: number) => Chunk.NonEmptyChunk<number>

Builds a NonEmptyChunk from an non-empty collection of elements.

@since2.0.0

make
(1, 2, 3))
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const runPromise: <Chunk.Chunk<number>, never>(effect: Effect.Effect<Chunk.Chunk<number>, never, never>, options?: {
readonly signal?: AbortSignal;
} | undefined) => Promise<...>

Executes an effect and returns the result as a Promise.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk.Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
)).
Promise<Chunk<number>>.then<void, never>(onfulfilled?: ((value: Chunk.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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 1, 2, 3 ] }

Moreover, you can create a stream from multiple Chunks as well:

import {
import Stream
Stream
,
import Chunk
Chunk
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
// Creating a stream with values from multiple Chunks
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
const fromChunks: <number>(...chunks: Chunk.Chunk<number>[]) => Stream.Stream<number, never, never>

Creates a stream from an arbitrary number of chunks.

@example

import { Chunk, Effect, Stream } from "effect"
// Creating a stream with values from multiple Chunks
const stream = Stream.fromChunks(Chunk.make(1, 2, 3), Chunk.make(4, 5, 6))
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 1, 2, 3, 4, 5, 6 ] }

@since2.0.0

fromChunks
(
import Chunk
Chunk
.
const make: <[number, number, number]>(as_0: number, as_1: number, as_2: number) => Chunk.NonEmptyChunk<number>

Builds a NonEmptyChunk from an non-empty collection of elements.

@since2.0.0

make
(1, 2, 3),
import Chunk
Chunk
.
const make: <[number, number, number]>(as_0: number, as_1: number, as_2: number) => Chunk.NonEmptyChunk<number>

Builds a NonEmptyChunk from an non-empty collection of elements.

@since2.0.0

make
(4, 5, 6))
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const runPromise: <Chunk.Chunk<number>, never>(effect: Effect.Effect<Chunk.Chunk<number>, never, never>, options?: {
readonly signal?: AbortSignal;
} | undefined) => Promise<...>

Executes an effect and returns the result as a Promise.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk.Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
)).
Promise<Chunk<number>>.then<void, never>(onfulfilled?: ((value: Chunk.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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 1, 2, 3, 4, 5, 6 ] }

You can generate a stream from an Effect workflow by employing the Stream.fromEffect constructor. For instance, consider the following stream, which generates a single random number:

import {
import Stream
Stream
,
import Random
Random
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
const fromEffect: <number, never, never>(effect: Effect.Effect<number, never, never>) => Stream.Stream<number, never, never>

Either emits the success value of this effect or terminates the stream with the failure value of this effect.

@example

import { Effect, Random, Stream } from "effect"
const stream = Stream.fromEffect(Random.nextInt)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// Example Output: { _id: 'Chunk', values: [ 922694024 ] }

@since2.0.0

fromEffect
(
import Random
Random
.
const nextInt: Effect.Effect<number, never, never>

Returns the next integer value from the pseudo-random number generator.

@since2.0.0

nextInt
)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

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.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
)).
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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// Example Output: { _id: 'Chunk', values: [ 1042302242 ] }

This method allows you to seamlessly transform the output of an Effect into a stream, providing a straightforward way to work with asynchronous operations within your streams.

Imagine you have an asynchronous function that relies on callbacks. If you want to capture the results emitted by those callbacks as a stream, you can use the Stream.async function. This function is designed to adapt functions that invoke their callbacks multiple times and emit the results as a stream.

Let’s break down how to use it in the following example:

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
,
import Chunk
Chunk
,
import Option

@since2.0.0

@since2.0.0

Option
,
import StreamEmit
StreamEmit
} from "effect"
const
const events: number[]
events
= [1, 2, 3, 4]
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
async<number, never, never>(register: (emit: StreamEmit.Emit<never, never, number, void>) => void | Effect.Effect<void, never, never>, bufferSize?: number | "unbounded" | {
readonly bufferSize?: number | undefined;
readonly strategy?: "dropping" | "sliding" | "suspend" | undefined;
} | undefined): Stream.Stream<...>
export async

Creates a stream from an asynchronous callback that can be called multiple times. The optionality of the error type E in Emit can be used to signal the end of the stream by setting it to None.

The registration function can optionally return an Effect, which will be executed if the Fiber executing this Effect is interrupted.

@example

import type { StreamEmit } from "effect"
import { Chunk, Effect, Option, Stream } from "effect"
const events = [1, 2, 3, 4]
const stream = Stream.async(
(emit: StreamEmit.Emit<never, never, number, void>) => {
events.forEach((n) => {
setTimeout(() => {
if (n === 3) {
emit(Effect.fail(Option.none())) // Terminate the stream
} else {
emit(Effect.succeed(Chunk.of(n))) // Add the current item to the stream
}
}, 100 * n)
})
}
)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 1, 2 ] }

@since2.0.0

async
(
(
emit: StreamEmit.Emit<never, never, number, void>
emit
:
import StreamEmit
StreamEmit
.
interface Emit<in R, in E, in A, out B>

An Emit<R, E, A, B> represents an asynchronous callback that can be called multiple times. The callback can be called with a value of type Effect<Chunk<A>, Option<E>, R>, where succeeding with a Chunk<A> indicates to emit those elements, failing with Some<E> indicates to terminate with that error, and failing with None indicates to terminate with an end of stream signal.

@since2.0.0

Emit
<never, never, number, void>) => {
const events: number[]
events
.
Array<number>.forEach(callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any): void

Performs the specified action for each element in an array.

@paramcallbackfn A function that accepts up to three arguments. forEach calls the callbackfn function one time for each element in the array.

@paramthisArg An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.

forEach
((
n: number
n
) => {
function setTimeout<[]>(callback: () => void, ms?: number): NodeJS.Timeout (+1 overload)

Schedules execution of a one-time callback after delay milliseconds.

The callback will likely not be invoked in precisely delay milliseconds. Node.js makes no guarantees about the exact timing of when callbacks will fire, nor of their ordering. The callback will be called as close as possible to the time specified.

When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.

If callback is not a function, a TypeError will be thrown.

This method has a custom variant for promises that is available using timersPromises.setTimeout().

@sincev0.0.1

@paramcallback The function to call when the timer elapses.

@paramdelay The number of milliseconds to wait before calling the callback.

@paramargs Optional arguments to pass when the callback is called.

setTimeout
(() => {
if (
n: number
n
=== 3) {
// Terminate the stream
emit: StreamEmit.Emit
(f: Effect.Effect<Chunk.Chunk<number>, Option.Option<never>, never>) => Promise<void>
emit
(
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const fail: <Option.Option<never>>(error: Option.Option<never>) => Effect.Effect<never, Option.Option<never>, never>

Creates an Effect that represents a recoverable error.

When to Use

Use this function to explicitly signal an error in an Effect. The error will keep propagating unless it is handled. You can handle the error with functions like

catchAll

or

catchTag

.

@seesucceed to create an effect that represents a successful value.

@example

// Title: Creating a Failed Effect
import { Effect } from "effect"
// ┌─── Effect<never, Error, never>
// ▼
const failure = Effect.fail(
new Error("Operation failed due to network error")
)

@since2.0.0

fail
(
import Option

@since2.0.0

@since2.0.0

Option
.
const none: <never>() => Option.Option<never>

Represents the absence of a value by creating an empty Option.

Option.none returns an Option<never>, which is a subtype of Option<A>. This means you can use it in place of any Option<A> regardless of the type A.

@seesome for the opposite operation.

@example

// Title: Creating an Option with No Value
import { Option } from "effect"
// An Option holding no value
//
// ┌─── Option<never>
// ▼
const noValue = Option.none()
console.log(noValue)
// Output: { _id: 'Option', _tag: 'None' }

@since2.0.0

none
()))
} else {
// Add the current item to the stream
emit: StreamEmit.Emit
(f: Effect.Effect<Chunk.Chunk<number>, Option.Option<never>, never>) => Promise<void>
emit
(
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const succeed: <Chunk.NonEmptyChunk<number>>(value: Chunk.NonEmptyChunk<number>) => Effect.Effect<Chunk.NonEmptyChunk<number>, never, never>

Creates an Effect that always succeeds with a given value.

When to Use

Use this function when you need an effect that completes successfully with a specific value without any errors or external dependencies.

@seefail to create an effect that represents a failure.

@example

// Title: Creating a Successful Effect
import { Effect } from "effect"
// Creating an effect that represents a successful scenario
//
// ┌─── Effect<number, never, never>
// ▼
const success = Effect.succeed(42)

@since2.0.0

succeed
(
import Chunk
Chunk
.
const of: <number>(a: number) => Chunk.NonEmptyChunk<number>

Builds a NonEmptyChunk from a single element.

@since2.0.0

of
(
n: number
n
)))
}
}, 100 *
n: number
n
)
})
}
)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const runPromise: <Chunk.Chunk<number>, never>(effect: Effect.Effect<Chunk.Chunk<number>, never, never>, options?: {
readonly signal?: AbortSignal;
} | undefined) => Promise<...>

Executes an effect and returns the result as a Promise.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk.Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
)).
Promise<Chunk<number>>.then<void, never>(onfulfilled?: ((value: Chunk.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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 1, 2 ] }

The StreamEmit.Emit<R, E, A, void> type represents an asynchronous callback that can be called multiple times. This callback takes a value of type Effect<Chunk<A>, Option<E>, R>. Here’s what each of the possible outcomes means:

  • When the value provided to the callback results in a Chunk<A> upon success, it signifies that the specified elements should be emitted as part of the stream.

  • If the value passed to the callback results in a failure with Some<E>, it indicates the termination of the stream with the specified error.

  • When the value passed to the callback results in a failure with None, it serves as a signal for the end of the stream, essentially terminating it.

To put it simply, this type allows you to specify how your asynchronous callback interacts with the stream, determining when to emit elements, when to terminate with an error, or when to signal the end of the stream.

You can create a pure stream from an Iterable of values using the Stream.fromIterable constructor. It’s a straightforward way to convert a collection of values into a stream.

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
const
const numbers: number[]
numbers
= [1, 2, 3]
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
const fromIterable: <number>(iterable: Iterable<number>) => Stream.Stream<number, never, never>

Creates a new Stream from an iterable collection of values.

@example

import { Effect, Stream } from "effect"
const numbers = [1, 2, 3]
const stream = Stream.fromIterable(numbers)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 1, 2, 3 ] }

@since2.0.0

fromIterable
(
const numbers: number[]
numbers
)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

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.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
)).
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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 1, 2, 3 ] }

When you have an effect that produces a value of type Iterable, you can employ the Stream.fromIterableEffect constructor to generate a stream from that effect.

For instance, let’s say you have a database operation that retrieves a list of users. Since this operation involves effects, you can utilize Stream.fromIterableEffect to convert the result into a Stream:

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
,
import Context

@since2.0.0

@since2.0.0

Context
} from "effect"
class
class Database
Database
extends
import Context

@since2.0.0

@since2.0.0

Context
.
const Tag: <"Database">(id: "Database") => <Self, Shape>() => Context.TagClass<Self, "Database", Shape>

@example

import { Context, Layer } from "effect"
class MyTag extends Context.Tag("MyTag")<
MyTag,
{ readonly myNum: number }
>() {
static Live = Layer.succeed(this, { myNum: 108 })
}

@since2.0.0

Tag
("Database")<
class Database
Database
,
{ readonly
getUsers: Effect.Effect<string[], never, never>
getUsers
:
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
interface Effect<out A, out E = never, out R = never>

The Effect interface defines a value that describes a workflow or job, which can succeed or fail.

Details

The Effect interface represents a computation that can model a workflow involving various types of operations, such as synchronous, asynchronous, concurrent, and parallel interactions. It operates within a context of type R, and the result can either be a success with a value of type A or a failure with an error of type E. The Effect is designed to handle complex interactions with external resources, offering advanced features such as fiber-based concurrency, scheduling, interruption handling, and scalability. This makes it suitable for tasks that require fine-grained control over concurrency and error management.

To execute an Effect value, you need a Runtime, which provides the environment necessary to run and manage the computation.

@since2.0.0

@since2.0.0

Effect
<
interface Array<T>
Array
<string>> }
>() {}
const
const getUsers: Effect.Effect<string[], never, Database>
getUsers
=
class Database
Database
.
Pipeable.pipe<typeof Database, Effect.Effect<string[], never, Database>>(this: typeof Database, ab: (_: typeof Database) => Effect.Effect<string[], never, Database>): Effect.Effect<...> (+21 overloads)
pipe
(
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const andThen: <{
readonly getUsers: Effect.Effect<Array<string>>;
}, Effect.Effect<string[], never, never>>(f: (a: {
readonly getUsers: Effect.Effect<Array<string>>;
}) => Effect.Effect<string[], never, never>) => <E, R>(self: Effect.Effect<...>) => Effect.Effect<...> (+3 overloads)

Chains two actions, where the second action can depend on the result of the first.

Syntax

const transformedEffect = pipe(myEffect, Effect.andThen(anotherEffect))
// or
const transformedEffect = Effect.andThen(myEffect, anotherEffect)
// or
const transformedEffect = myEffect.pipe(Effect.andThen(anotherEffect))

When to Use

Use andThen when you need to run multiple actions in sequence, with the second action depending on the result of the first. This is useful for combining effects or handling computations that must happen in order.

Details

The second action can be:

  • A constant value (similar to

as

)

  • A function returning a value (similar to

map

)

  • A Promise
  • A function returning a Promise
  • An Effect
  • A function returning an Effect (similar to

flatMap

)

Note: andThen works well with both Option and Either types, treating them as effects.

@example

// Title: Applying a Discount Based on Fetched Amount
import { pipe, Effect } from "effect"
// Function to apply a discount safely to a transaction amount
const applyDiscount = (
total: number,
discountRate: number
): Effect.Effect<number, Error> =>
discountRate === 0
? Effect.fail(new Error("Discount rate cannot be zero"))
: Effect.succeed(total - (total * discountRate) / 100)
// Simulated asynchronous task to fetch a transaction amount from database
const fetchTransactionAmount = Effect.promise(() => Promise.resolve(100))
// Using Effect.map and Effect.flatMap
const result1 = pipe(
fetchTransactionAmount,
Effect.map((amount) => amount * 2),
Effect.flatMap((amount) => applyDiscount(amount, 5))
)
// Effect.runPromise(result1).then(console.log)
// Output: 190
// Using Effect.andThen
const result2 = pipe(
fetchTransactionAmount,
Effect.andThen((amount) => amount * 2),
Effect.andThen((amount) => applyDiscount(amount, 5))
)
// Effect.runPromise(result2).then(console.log)
// Output: 190

@since2.0.0

andThen
((
_: {
readonly getUsers: Effect.Effect<Array<string>>;
}
_
) =>
_: {
readonly getUsers: Effect.Effect<Array<string>>;
}
_
.
getUsers: Effect.Effect<string[], never, never>
getUsers
))
const
const stream: Stream.Stream<string, never, Database>
stream
=
import Stream
Stream
.
const fromIterableEffect: <string, never, Database>(effect: Effect.Effect<Iterable<string>, never, Database>) => Stream.Stream<string, never, Database>

Creates a stream from an effect producing a value of type Iterable<A>.

@example

import { Context, Effect, Stream } from "effect"
class Database extends Context.Tag("Database")<
Database,
{ readonly getUsers: Effect.Effect<Array<string>> }
>() {}
const getUsers = Database.pipe(Effect.andThen((_) => _.getUsers))
const stream = Stream.fromIterableEffect(getUsers)
// Effect.runPromise(
// Stream.runCollect(stream.pipe(Stream.provideService(Database, { getUsers: Effect.succeed(["user1", "user2"]) })))
// ).then(console.log)
// { _id: 'Chunk', values: [ 'user1', 'user2' ] }

@since2.0.0

fromIterableEffect
(
const getUsers: Effect.Effect<string[], never, Database>
getUsers
)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const runPromise: <Chunk<string>, never>(effect: Effect.Effect<Chunk<string>, never, never>, options?: {
readonly signal?: AbortSignal;
} | undefined) => Promise<Chunk<string>>

Executes an effect and returns the result as a Promise.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <string, never, never>(self: Stream.Stream<string, never, never>) => Effect.Effect<Chunk<string>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<string, never, Database>
stream
.
Pipeable.pipe<Stream.Stream<string, never, Database>, Stream.Stream<string, never, never>>(this: Stream.Stream<...>, ab: (_: Stream.Stream<string, never, Database>) => Stream.Stream<...>): Stream.Stream<...> (+21 overloads)
pipe
(
import Stream
Stream
.
const provideService: <typeof Database>(tag: typeof Database, resource: {
readonly getUsers: Effect.Effect<Array<string>>;
}) => <A, E, R>(self: Stream.Stream<A, E, R>) => Stream.Stream<...> (+1 overload)

Provides the stream with the single service it requires. If the stream requires more than one service use Stream.provideContext instead.

@since2.0.0

provideService
(
class Database
Database
, {
getUsers: Effect.Effect<string[], never, never>
getUsers
:
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const succeed: <string[]>(value: string[]) => Effect.Effect<string[], never, never>

Creates an Effect that always succeeds with a given value.

When to Use

Use this function when you need an effect that completes successfully with a specific value without any errors or external dependencies.

@seefail to create an effect that represents a failure.

@example

// Title: Creating a Successful Effect
import { Effect } from "effect"
// Creating an effect that represents a successful scenario
//
// ┌─── Effect<number, never, never>
// ▼
const success = Effect.succeed(42)

@since2.0.0

succeed
(["user1", "user2"])
})
)
)
).
Promise<Chunk<string>>.then<void, never>(onfulfilled?: ((value: Chunk<string>) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<never>) | null | undefined): Promise<...>

Attaches callbacks for the resolution and/or rejection of the Promise.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 'user1', 'user2' ] }

This enables you to work seamlessly with effects and convert their results into streams for further processing.

Async iterables are another type of data source that can be converted into a stream. With the Stream.fromAsyncIterable constructor, you can work with asynchronous data sources and handle potential errors gracefully.

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
const
const myAsyncIterable: () => AsyncGenerator<1 | 2, void, unknown>
myAsyncIterable
= async function* () {
yield 1
yield 2
}
const
const stream: Stream.Stream<1 | 2, Error, never>
stream
=
import Stream
Stream
.
const fromAsyncIterable: <1 | 2, Error>(iterable: AsyncIterable<1 | 2>, onError: (e: unknown) => Error) => Stream.Stream<1 | 2, Error, never>

Creates a stream from an AsyncIterable.

@example

import { Effect, Stream } from "effect"
const myAsyncIterable = async function*() {
yield 1
yield 2
}
const stream = Stream.fromAsyncIterable(
myAsyncIterable(),
(e) => new Error(String(e)) // Error Handling
)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 1, 2 ] }

@since2.0.0

fromAsyncIterable
(
const myAsyncIterable: () => AsyncGenerator<1 | 2, void, unknown>
myAsyncIterable
(),
(
e: unknown
e
) => new
var Error: ErrorConstructor
new (message?: string) => Error
Error
(
var String: StringConstructor
(value?: any) => string

Allows manipulation and formatting of text strings and determination and location of substrings within strings.

String
(
e: unknown
e
)) // Error Handling
)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
.
const runPromise: <Chunk<1 | 2>, Error>(effect: Effect.Effect<Chunk<1 | 2>, Error, never>, options?: {
readonly signal?: AbortSignal;
} | undefined) => Promise<...>

Executes an effect and returns the result as a Promise.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <1 | 2, Error, never>(self: Stream.Stream<1 | 2, Error, never>) => Effect.Effect<Chunk<1 | 2>, Error, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<1 | 2, Error, never>
stream
)).
Promise<Chunk<1 | 2>>.then<void, never>(onfulfilled?: ((value: Chunk<1 | 2>) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<never>) | null | undefined): Promise<...>

Attaches callbacks for the resolution and/or rejection of the Promise.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 1, 2 ] }

In this code, we define an async iterable and then create a stream named stream from it. Additionally, we provide an error handler function to manage any potential errors that may occur during the conversion.

You can create a stream that endlessly repeats a specific value using the Stream.repeatValue constructor:

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
} from "effect"
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
const repeatValue: <number>(value: number) => Stream.Stream<number, never, never>

Repeats the provided value infinitely.

@example

import { Effect, Stream } from "effect"
const stream = Stream.repeatValue(0)
// Effect.runPromise(Stream.runCollect(stream.pipe(Stream.take(5)))).then(console.log)
// { _id: 'Chunk', values: [ 0, 0, 0, 0, 0 ] }

@since2.0.0

repeatValue
(0)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

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.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
.
Pipeable.pipe<Stream.Stream<number, never, never>, Stream.Stream<number, never, never>>(this: Stream.Stream<...>, ab: (_: Stream.Stream<number, never, never>) => Stream.Stream<number, never, never>): Stream.Stream<...> (+21 overloads)
pipe
(
import Stream
Stream
.
const take: (n: number) => <A, E, R>(self: Stream.Stream<A, E, R>) => Stream.Stream<A, E, R> (+1 overload)

Takes the specified number of elements from this stream.

@example

import { Effect, Stream } from "effect"
const stream = Stream.take(Stream.iterate(0, (n) => n + 1), 5)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 0, 1, 2, 3, 4 ] }

@since2.0.0

take
(5)))).
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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 0, 0, 0, 0, 0 ] }

Stream.repeat allows you to create a stream that repeats a specified stream’s content according to a schedule. This can be useful for generating recurring events or values.

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
,
import Schedule
Schedule
} from "effect"
// Creating a stream that repeats a value indefinitely
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
const repeat: <number, never, never, number, never>(self: Stream.Stream<number, never, never>, schedule: Schedule.Schedule<number, unknown, never>) => Stream.Stream<number, never, never> (+1 overload)

Repeats the entire stream using the specified schedule. The stream will execute normally, and then repeat again according to the provided schedule.

@example

import { Effect, Schedule, Stream } from "effect"
const stream = Stream.repeat(Stream.succeed(1), Schedule.forever)
// Effect.runPromise(Stream.runCollect(stream.pipe(Stream.take(5)))).then(console.log)
// { _id: 'Chunk', values: [ 1, 1, 1, 1, 1 ] }

@since2.0.0

repeat
(
import Stream
Stream
.
const succeed: <number>(value: number) => Stream.Stream<number, never, never>

Creates a single-valued pure stream.

@example

import { Effect, Stream } from "effect"
// A Stream with a single number
const stream = Stream.succeed(3)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 3 ] }

@since2.0.0

succeed
(1),
import Schedule
Schedule
.
const forever: Schedule.Schedule<number, unknown, never>

A schedule that always recurs, producing a count of repeats: 0, 1, 2.

@since2.0.0

forever
)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

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.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
.
Pipeable.pipe<Stream.Stream<number, never, never>, Stream.Stream<number, never, never>>(this: Stream.Stream<...>, ab: (_: Stream.Stream<number, never, never>) => Stream.Stream<number, never, never>): Stream.Stream<...> (+21 overloads)
pipe
(
import Stream
Stream
.
const take: (n: number) => <A, E, R>(self: Stream.Stream<A, E, R>) => Stream.Stream<A, E, R> (+1 overload)

Takes the specified number of elements from this stream.

@example

import { Effect, Stream } from "effect"
const stream = Stream.take(Stream.iterate(0, (n) => n + 1), 5)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 0, 1, 2, 3, 4 ] }

@since2.0.0

take
(5)))).
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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
// { _id: 'Chunk', values: [ 1, 1, 1, 1, 1 ] }

Imagine you have an effectful API call, and you want to use the result of that call to create a stream. You can achieve this by creating a stream from the effect and repeating it indefinitely.

Here’s an example of generating a stream of random numbers:

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
,
import Random
Random
} from "effect"
const
const stream: Stream.Stream<number, never, never>
stream
=
import Stream
Stream
.
const repeatEffect: <number, never, never>(effect: Effect.Effect<number, never, never>) => Stream.Stream<number, never, never>

Creates a stream from an effect producing a value of type A which repeats forever.

@example

import { Effect, Random, Stream } from "effect"
const stream = Stream.repeatEffect(Random.nextInt)
// Effect.runPromise(Stream.runCollect(stream.pipe(Stream.take(5)))).then(console.log)
// Example Output: { _id: 'Chunk', values: [ 3891571149, 4239494205, 2352981603, 2339111046, 1488052210 ] }

@since2.0.0

repeatEffect
(
import Random
Random
.
const nextInt: Effect.Effect<number, never, never>

Returns the next integer value from the pseudo-random number generator.

@since2.0.0

nextInt
)
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

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.

Details

This function runs an effect and converts its result into a Promise. If the effect succeeds, the Promise will resolve with the successful result. If the effect fails, the Promise will reject with an error, which includes the failure details of the effect.

The optional options parameter allows you to pass an AbortSignal for cancellation, enabling more fine-grained control over asynchronous tasks.

When to Use

Use this function when you need to execute an effect and work with its result in a promise-based system, such as when integrating with third-party libraries that expect Promise results.

@seerunPromiseExit 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

@since2.0.0

runPromise
(
import Stream
Stream
.
const runCollect: <number, never, never>(self: Stream.Stream<number, never, never>) => Effect.Effect<Chunk<number>, never, never>

Runs the stream and collects all of its elements to a chunk.

@since2.0.0

runCollect
(
const stream: Stream.Stream<number, never, never>
stream
.
Pipeable.pipe<Stream.Stream<number, never, never>, Stream.Stream<number, never, never>>(this: Stream.Stream<...>, ab: (_: Stream.Stream<number, never, never>) => Stream.Stream<number, never, never>): Stream.Stream<...> (+21 overloads)
pipe
(
import Stream
Stream
.
const take: (n: number) => <A, E, R>(self: Stream.Stream<A, E, R>) => Stream.Stream<A, E, R> (+1 overload)

Takes the specified number of elements from this stream.

@example

import { Effect, Stream } from "effect"
const stream = Stream.take(Stream.iterate(0, (n) => n + 1), 5)
// Effect.runPromise(Stream.runCollect(stream)).then(console.log)
// { _id: 'Chunk', values: [ 0, 1, 2, 3, 4 ] }

@since2.0.0

take
(5)))).
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.

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA 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

@seesource

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.

@sincev0.1.100

log
)
/*
Example Output:
{
_id: 'Chunk',
values: [ 1666935266, 604851965, 2194299958, 3393707011, 4090317618 ]
}
*/

You can repeatedly evaluate a given effect and terminate the stream based on specific conditions.

In this example, we’re draining an Iterator to create a stream from it:

import {
import Stream
Stream
,
import Effect

@since2.0.0

@since2.0.0

@since2.0.0

Effect
,
import Option

@since2.0.0

@since2.0.0

Option
} from "effect"
const
const drainIterator: <A>(it: Iterator<A>) => Stream.Stream<A>
drainIterator
= <
function (type parameter) A in <A>(it: Iterator<A>): Stream.Stream<A>
A
>(
it: Iterator<A, any, any>
it
:
interface Iterator<T, TReturn = any, TNext