Tracing in Effect

Although logs and metrics are useful to understand the behavior of individual services, they are not enough to provide a complete overview of the lifetime of a request in a distributed system.

In a distributed system, a request can span multiple services and each service can make multiple requests to other services to fulfill the request. In such a scenario, we need to have a way to track the lifetime of a request across multiple services to diagnose what services are the bottlenecks and where the request is spending most of its time.

Spans

A span represents a single unit of work or operation within a request. It provides a detailed view of what happened during the execution of that specific operation.

Each span typically contains the following information:

Span Component	Description
Name	Describes the specific operation being tracked.
Timing Data	Timestamps indicating when the operation started and its duration.
Log Messages	Structured logs capturing important events during the operation.
Attributes	Metadata providing additional context about the operation.

Spans are key building blocks in tracing, helping you visualize and understand the flow of requests through various services.

Traces

A trace records the paths taken by requests (made by an application or end-user) as they propagate through multi-service architectures, like microservice and serverless applications.

Without tracing, it is challenging to pinpoint the cause of performance problems in a distributed system.

A trace is made of one or more spans. The first span represents the root span. Each root span represents a request from start to finish. The spans underneath the parent provide a more in-depth context of what occurs during a request (or what steps make up a request).

Many Observability back-ends visualize traces as waterfall diagrams that may look something like this:

Trace Waterfall Diagram

Waterfall diagrams show the parent-child relationship between a root span and its child spans. When a span encapsulates another span, this also represents a nested relationship.

Creating Spans

You can add tracing to an effect by creating a span using the Effect.withSpan API. This helps you track specific operations within the effect.

Example (Adding a Span to an Effect)

1
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
2

3
// Define an effect that delays for 100 milliseconds
4
const 
const program: Effect.Effect<void, never, never>
program = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const void: Effect.Effect<void, never, never>
export void
Represents an effect that does nothing and produces no value.
When to Use
Use this effect when you need to represent an effect that does nothing.
This is useful in scenarios where you need to satisfy an effect-based
interface or control program flow without performing any operations. For
example, it can be used in situations where you want to return an effect
from a function but do not need to compute or return any result.
@since ― 2.0.0
void.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const delay: (duration: DurationInput) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R> (+1 overload)
Delays the execution of an effect by a specified Duration.
**Details
This function postpones the execution of the provided effect by the specified
duration. The duration can be provided in various formats supported by the
Duration module.
Internally, this function does not block the thread; instead, it uses an
efficient, non-blocking mechanism to introduce the delay.
@example 
import { Console, Effect } from "effect"

const task = Console.log("Task executed")

const program = Console.log("start").pipe(
  Effect.andThen(
    // Delays the log message by 2 seconds
    task.pipe(Effect.delay("2 seconds"))
  )
)

// Effect.runFork(program)
// Output:
// start
// Task executed
@since ― 2.0.0
delay("100 millis"))
5

6
// Instrument the effect with a span for tracing
7
const 
const instrumented: Effect.Effect<void, never, never>
instrumented = 
const program: Effect.Effect<void, never, never>
program.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const withSpan: (name: string, options?: SpanOptions | undefined) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, ParentSpan>> (+1 overload)
Wraps the effect with a new span for tracing.
@since ― 2.0.0
withSpan("myspan"))

Instrumenting an effect with a span does not change its type. If you start with an Effect<A, E, R>, the result remains an Effect<A, E, R>.

Printing Spans

To print spans for debugging or analysis, you’ll need to install the required tracing tools. Here’s how to set them up for your project.

Installing Dependencies

Choose your package manager and install the necessary libraries:

# Install the main library for integrating OpenTelemetry with Effect
npm install @effect/opentelemetry

# Install the required OpenTelemetry SDKs for tracing and metrics
npm install @opentelemetry/sdk-trace-base
npm install @opentelemetry/sdk-trace-node
npm install @opentelemetry/sdk-trace-web
npm install @opentelemetry/sdk-metrics

# Install the main library for integrating OpenTelemetry with Effect
pnpm add @effect/opentelemetry

# Install the required OpenTelemetry SDKs for tracing and metrics
pnpm add @opentelemetry/sdk-trace-base
pnpm add @opentelemetry/sdk-trace-node
pnpm add @opentelemetry/sdk-trace-web
pnpm add @opentelemetry/sdk-metrics

# Install the main library for integrating OpenTelemetry with Effect
yarn add @effect/opentelemetry

# Install the required OpenTelemetry SDKs for tracing and metrics
yarn add @opentelemetry/sdk-trace-base
yarn add @opentelemetry/sdk-trace-node
yarn add @opentelemetry/sdk-trace-web
yarn add @opentelemetry/sdk-metrics

# Install the main library for integrating OpenTelemetry with Effect
bun add @effect/opentelemetry

# Install the required OpenTelemetry SDKs for tracing and metrics
bun add @opentelemetry/sdk-trace-base
bun add @opentelemetry/sdk-trace-node
bun add @opentelemetry/sdk-trace-web
bun add @opentelemetry/sdk-metrics

Printing a Span to the Console

Once the dependencies are installed, you can set up span printing using OpenTelemetry. Here’s an example showing how to print a span for an effect.

Example (Setting Up and Printing a Span)

1
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
2
import { 
import NodeSdk
NodeSdk } from "@effect/opentelemetry"
3
import {
4
  
class ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter,
5
  
class BatchSpanProcessor
BatchSpanProcessor
6
} from "@opentelemetry/sdk-trace-base"
7

8
// Define an effect that delays for 100 milliseconds
9
const 
const program: Effect.Effect<void, never, never>
program = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const void: Effect.Effect<void, never, never>
export void
Represents an effect that does nothing and produces no value.
When to Use
Use this effect when you need to represent an effect that does nothing.
This is useful in scenarios where you need to satisfy an effect-based
interface or control program flow without performing any operations. For
example, it can be used in situations where you want to return an effect
from a function but do not need to compute or return any result.
@since ― 2.0.0
void.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const delay: (duration: DurationInput) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R> (+1 overload)
Delays the execution of an effect by a specified Duration.
**Details
This function postpones the execution of the provided effect by the specified
duration. The duration can be provided in various formats supported by the
Duration module.
Internally, this function does not block the thread; instead, it uses an
efficient, non-blocking mechanism to introduce the delay.
@example 
import { Console, Effect } from "effect"

const task = Console.log("Task executed")

const program = Console.log("start").pipe(
  Effect.andThen(
    // Delays the log message by 2 seconds
    task.pipe(Effect.delay("2 seconds"))
  )
)

// Effect.runFork(program)
// Output:
// start
// Task executed
@since ― 2.0.0
delay("100 millis"))
10

11
// Instrument the effect with a span for tracing
12
const 
const instrumented: Effect.Effect<void, never, never>
instrumented = 
const program: Effect.Effect<void, never, never>
program.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const withSpan: (name: string, options?: SpanOptions | undefined) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, ParentSpan>> (+1 overload)
Wraps the effect with a new span for tracing.
@since ― 2.0.0
withSpan("myspan"))
13

14
// Set up tracing with the OpenTelemetry SDK
15
const 
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive = 
import NodeSdk
NodeSdk.
const layer: (evaluate: LazyArg<NodeSdk.Configuration>) => Layer<Resource> (+1 overload)@since ― 1.0.0
layer(() => ({
16
  
Configuration.resource?: {
    readonly serviceName: string;
    readonly serviceVersion?: string;
    readonly attributes?: ResourceAttributes;
} | undefined
resource: { 
serviceName: string
serviceName: "example" },
17
  // Export span data to the console
18
  
Configuration.spanProcessor?: SpanProcessor | readonly SpanProcessor[] | undefined
spanProcessor: new 
new BatchSpanProcessor<BufferConfig>(_exporter: SpanExporter, config?: BufferConfig | undefined): BatchSpanProcessor
BatchSpanProcessor(new 
new ConsoleSpanExporter(): ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter())
19
}))
20

21
// Run the effect, providing the tracing layer
22
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const runPromise: <void, never>(effect: Effect.Effect<void, never, never>, options?: {
    readonly signal?: AbortSignal;
} | undefined) => Promise<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.
@see ― runPromiseExit for a version that returns an Exit type instead
of rejecting.
@example 
// Title: Running a Successful Effect as a Promise
import { Effect } from "effect"

// Effect.runPromise(Effect.succeed(1)).then(console.log)
// Output: 1
@example 
//Example: Handling a Failing Effect as a Rejected Promise
import { Effect } from "effect"
// Effect.runPromise(Effect.fail("my error")).catch(console.error)
// Output:
// (FiberFailure) Error: my error
@since ― 2.0.0
runPromise(
const instrumented: Effect.Effect<void, never, never>
instrumented.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const provide: <Resource, never, never>(layer: Layer<Resource, never, never>) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, Resource>> (+9 overloads)
Provides necessary dependencies to an effect, removing its environmental
requirements.
Details
This function allows you to supply the required environment for an effect.
The environment can be provided in the form of one or more Layers, a
Context, a Runtime, or a ManagedRuntime. Once the environment is
provided, the effect can run without requiring external dependencies.
You can compose layers to create a modular and reusable way of setting up the
environment for effects. For example, layers can be used to configure
databases, logging services, or any other required dependencies.
@see ― provideService for providing a service to an effect.
@example 
import { Context, Effect, Layer } from "effect"

class Database extends Context.Tag("Database")<
  Database,
  { readonly query: (sql: string) => Effect.Effect<Array<unknown>> }
>() {}

const DatabaseLive = Layer.succeed(
  Database,
  {
    // Simulate a database query
    query: (sql: string) => Effect.log(`Executing query: ${sql}`).pipe(Effect.as([]))
  }
)

//      ┌─── Effect<unknown[], never, Database>
//      ▼
const program = Effect.gen(function*() {
  const database = yield* Database
  const result = yield* database.query("SELECT * FROM users")
  return result
})

//      ┌─── Effect<unknown[], never, never>
//      ▼
const runnable = Effect.provide(program, DatabaseLive)

// Effect.runPromise(runnable).then(console.log)
// Output:
// timestamp=... level=INFO fiber=#0 message="Executing query: SELECT * FROM users"
// []
@since ― 2.0.0
provide(
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive)))
23
/*
24
Example Output:
25
{
26
  resource: {
27
    attributes: {
28
      'service.name': 'example',
29
      'telemetry.sdk.language': 'nodejs',
30
      'telemetry.sdk.name': '@effect/opentelemetry',
31
      'telemetry.sdk.version': '1.28.0'
32
    }
33
  },
34
  instrumentationScope: { name: 'example', version: undefined, schemaUrl: undefined },
35
  traceId: '673c06608bd815f7a75bf897ef87e186',
36
  parentId: undefined,
37
  traceState: undefined,
38
  name: 'myspan',
39
  id: '401b2846170cd17b',
40
  kind: 0,
41
  timestamp: 1733220735529855.5,
42
  duration: 102079.958,
43
  attributes: {},
44
  status: { code: 1 },
45
  events: [],
46
  links: []
47
}
48
*/

Understanding the Span Output

The output provides detailed information about the span:

Field	Description
`traceId`	A unique identifier for the entire trace, helping trace requests or operations as they move through an application.
`parentId`	Identifies the parent span of the current span, marked as `undefined` in the output when there is no parent span, making it a root span.
`name`	Describes the name of the span, indicating the operation being tracked (e.g., “myspan”).
`id`	A unique identifier for the current span, distinguishing it from other spans within a trace.
`timestamp`	A timestamp representing when the span started, measured in microseconds since the Unix epoch.
`duration`	Specifies the duration of the span, representing the time taken to complete the operation (e.g., `2895.769` microseconds).
`attributes`	Spans may contain attributes, which are key-value pairs providing additional context or information about the operation. In this output, it’s an empty object, indicating no specific attributes in this span.
`status`	The status field provides information about the span’s status. In this case, it has a code of 1, which typically indicates an OK status (whereas a code of 2 signifies an ERROR status)
`events`	Spans can include events, which are records of specific moments during the span’s lifecycle. In this output, it’s an empty array, suggesting no specific events recorded.
`links`	Links can be used to associate this span with other spans in different traces. In the output, it’s an empty array, indicating no specific links for this span.

Span Capturing an Error

Here’s how a span looks when the effect encounters an error:

Example (Span for an Effect that Fails)

1
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
2
import { 
import NodeSdk
NodeSdk } from "@effect/opentelemetry"
3
import {
4
  
class ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter,
5
  
class BatchSpanProcessor
BatchSpanProcessor
6
} from "@opentelemetry/sdk-trace-base"
7

8
const 
const program: Effect.Effect<never, string, never>
program = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const fail: <string>(error: string) => Effect.Effect<never, string, 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
.
@see ― succeed 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")
)
@since ― 2.0.0
fail("Oh no!").
Pipeable.pipe<Effect.Effect<never, string, never>, Effect.Effect<never, string, never>, Effect.Effect<never, string, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<never, string, never>) => Effect.Effect<...>, bc: (_: Effect.Effect<...>) => Effect.Effect<...>): Effect.Effect<...> (+21 overloads)
pipe(
9
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const delay: (duration: DurationInput) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R> (+1 overload)
Delays the execution of an effect by a specified Duration.
**Details
This function postpones the execution of the provided effect by the specified
duration. The duration can be provided in various formats supported by the
Duration module.
Internally, this function does not block the thread; instead, it uses an
efficient, non-blocking mechanism to introduce the delay.
@example 
import { Console, Effect } from "effect"

const task = Console.log("Task executed")

const program = Console.log("start").pipe(
  Effect.andThen(
    // Delays the log message by 2 seconds
    task.pipe(Effect.delay("2 seconds"))
  )
)

// Effect.runFork(program)
// Output:
// start
// Task executed
@since ― 2.0.0
delay("100 millis"),
10
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const withSpan: (name: string, options?: SpanOptions | undefined) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, ParentSpan>> (+1 overload)
Wraps the effect with a new span for tracing.
@since ― 2.0.0
withSpan("myspan")
11
)
12

13
const 
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive = 
import NodeSdk
NodeSdk.
const layer: (evaluate: LazyArg<NodeSdk.Configuration>) => Layer<Resource> (+1 overload)@since ― 1.0.0
layer(() => ({
14
  
Configuration.resource?: {
    readonly serviceName: string;
    readonly serviceVersion?: string;
    readonly attributes?: ResourceAttributes;
} | undefined
resource: { 
serviceName: string
serviceName: "example" },
15
  
Configuration.spanProcessor?: SpanProcessor | readonly SpanProcessor[] | undefined
spanProcessor: new 
new BatchSpanProcessor<BufferConfig>(_exporter: SpanExporter, config?: BufferConfig | undefined): BatchSpanProcessor
BatchSpanProcessor(new 
new ConsoleSpanExporter(): ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter())
16
}))
17

18
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const runPromiseExit: <never, string>(effect: Effect.Effect<never, string, never>, options?: {
    readonly signal?: AbortSignal;
} | undefined) => Promise<Exit<never, string>>
Runs an effect and returns a Promise that resolves to an Exit,
representing the outcome.
Details
This function executes an effect and resolves to an Exit object. The Exit
type provides detailed information about the result of the effect:

If the effect succeeds, the Exit will be of type Success and include
the value produced by the effect.
If the effect fails, the Exit will be of type Failure and contain a
Cause object, detailing the failure.

Using this function allows you to examine both successful results and failure
cases in a unified way, while still leveraging Promise for handling the
asynchronous behavior of the effect.
When to Use
Use this function when you need to understand the outcome of an effect,
whether it succeeded or failed, and want to work with this result using
Promise syntax. This is particularly useful when integrating with systems
that rely on promises but need more detailed error handling than a simple
rejection.
@example 
// Title: Handling Results as Exit
import { Effect } from "effect"

// Execute a successful effect and get the Exit result as a Promise
// Effect.runPromiseExit(Effect.succeed(1)).then(console.log)
// Output:
// {
//   _id: "Exit",
//   _tag: "Success",
//   value: 1
// }

// Execute a failing effect and get the Exit result as a Promise
// Effect.runPromiseExit(Effect.fail("my error")).then(console.log)
// Output:
// {
//   _id: "Exit",
//   _tag: "Failure",
//   cause: {
//     _id: "Cause",
//     _tag: "Fail",
//     failure: "my error"
//   }
// }
@since ― 2.0.0
runPromiseExit(
const program: Effect.Effect<never, string, never>
program.
Pipeable.pipe<Effect.Effect<never, string, never>, Effect.Effect<never, string, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<never, string, never>) => Effect.Effect<never, string, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const provide: <Resource, never, never>(layer: Layer<Resource, never, never>) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, Resource>> (+9 overloads)
Provides necessary dependencies to an effect, removing its environmental
requirements.
Details
This function allows you to supply the required environment for an effect.
The environment can be provided in the form of one or more Layers, a
Context, a Runtime, or a ManagedRuntime. Once the environment is
provided, the effect can run without requiring external dependencies.
You can compose layers to create a modular and reusable way of setting up the
environment for effects. For example, layers can be used to configure
databases, logging services, or any other required dependencies.
@see ― provideService for providing a service to an effect.
@example 
import { Context, Effect, Layer } from "effect"

class Database extends Context.Tag("Database")<
  Database,
  { readonly query: (sql: string) => Effect.Effect<Array<unknown>> }
>() {}

const DatabaseLive = Layer.succeed(
  Database,
  {
    // Simulate a database query
    query: (sql: string) => Effect.log(`Executing query: ${sql}`).pipe(Effect.as([]))
  }
)

//      ┌─── Effect<unknown[], never, Database>
//      ▼
const program = Effect.gen(function*() {
  const database = yield* Database
  const result = yield* database.query("SELECT * FROM users")
  return result
})

//      ┌─── Effect<unknown[], never, never>
//      ▼
const runnable = Effect.provide(program, DatabaseLive)

// Effect.runPromise(runnable).then(console.log)
// Output:
// timestamp=... level=INFO fiber=#0 message="Executing query: SELECT * FROM users"
// []
@since ― 2.0.0
provide(
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive))).
Promise<Exit<never, string>>.then<void, never>(onfulfilled?: ((value: Exit<never, 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.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
19
  
var console: Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:

A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.

Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

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

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log
20
)
21
/*
22
Example Output:
23
{
24
  resource: {
25
    attributes: {
26
      'service.name': 'example',
27
      'telemetry.sdk.language': 'nodejs',
28
      'telemetry.sdk.name': '@effect/opentelemetry',
29
      'telemetry.sdk.version': '1.28.0'
30
    }
31
  },
32
  instrumentationScope: { name: 'example', version: undefined, schemaUrl: undefined },
33
  traceId: 'eee9619866179f209b7aae277283e71f',
34
  parentId: undefined,
35
  traceState: undefined,
36
  name: 'myspan',
37
  id: '3a5725c91884c9e1',
38
  kind: 0,
39
  timestamp: 1733220830575626,
40
  duration: 106578.042,
41
  attributes: {
42
    'code.stacktrace': 'at <anonymous> (/Users/giuliocanti/Documents/GitHub/website/content/dev/index.ts:10:10)'
43
  },
44
  status: { code: 2, message: 'Oh no!' },
45
  events: [
46
    {
47
      name: 'exception',
48
      attributes: {
49
        'exception.type': 'Error',
50
        'exception.message': 'Oh no!',
51
        'exception.stacktrace': 'Error: Oh no!'
52
      },
53
      time: [ 1733220830, 682204083 ],
54
      droppedAttributesCount: 0
55
    }
56
  ],
57
  links: []
58
}
59
{
60
  _id: 'Exit',
61
  _tag: 'Failure',
62
  cause: { _id: 'Cause', _tag: 'Fail', failure: 'Oh no!' }
63
}
64
*/

In this example, the span’s status code is 2, indicating an error. The message in the status provides more details about the failure.

Adding Annotations

You can provide extra information to a span by utilizing the Effect.annotateCurrentSpan function. This function allows you to attach key-value pairs, offering more context about the execution of the span.

Example (Annotating a Span)

1
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
2
import { 
import NodeSdk
NodeSdk } from "@effect/opentelemetry"
3
import {
4
  
class ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter,
5
  
class BatchSpanProcessor
BatchSpanProcessor
6
} from "@opentelemetry/sdk-trace-base"
7

8
const 
const program: Effect.Effect<void, never, never>
program = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const void: Effect.Effect<void, never, never>
export void
Represents an effect that does nothing and produces no value.
When to Use
Use this effect when you need to represent an effect that does nothing.
This is useful in scenarios where you need to satisfy an effect-based
interface or control program flow without performing any operations. For
example, it can be used in situations where you want to return an effect
from a function but do not need to compute or return any result.
@since ― 2.0.0
void.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>, Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<...>) => Effect.Effect<...>, bc: (_: Effect.Effect<...>) => Effect.Effect<...>, cd: (_: Effect.Effect<...>) => Effect.Effect<...>): Effect.Effect<...> (+21 overloads)
pipe(
9
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const delay: (duration: DurationInput) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R> (+1 overload)
Delays the execution of an effect by a specified Duration.
**Details
This function postpones the execution of the provided effect by the specified
duration. The duration can be provided in various formats supported by the
Duration module.
Internally, this function does not block the thread; instead, it uses an
efficient, non-blocking mechanism to introduce the delay.
@example 
import { Console, Effect } from "effect"

const task = Console.log("Task executed")

const program = Console.log("start").pipe(
  Effect.andThen(
    // Delays the log message by 2 seconds
    task.pipe(Effect.delay("2 seconds"))
  )
)

// Effect.runFork(program)
// Output:
// start
// Task executed
@since ― 2.0.0
delay("100 millis"),
10
  // Annotate the span with a key-value pair
11
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const tap: <void, Effect.Effect<void, never, never>>(f: (a: void) => Effect.Effect<void, never, never>) => <E, R>(self: Effect.Effect<void, E, R>) => Effect.Effect<...> (+7 overloads)
Runs a side effect with the result of an effect without changing the original
value.
Details
This function works similarly to flatMap, but it ignores the result of the
function passed to it. The value from the previous effect remains available
for the next part of the chain. Note that if the side effect fails, the
entire chain will fail too.
When to Use
Use this function when you want to perform a side effect, like logging or
tracking, without modifying the main value. This is useful when you need to
observe or record an action but want the original value to be passed to the
next step.
@see ― flatMap for a version that allows you to change the value.
@example 
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } 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))

const finalAmount = pipe(
  fetchTransactionAmount,
  // Log the fetched transaction amount
  Effect.tap((amount) => Console.log(`Apply a discount to: ${amount}`)),
  // `amount` is still available!
  Effect.flatMap((amount) => applyDiscount(amount, 5))
)

// Effect.runPromise(finalAmount).then(console.log)
// Output:
// Apply a discount to: 100
// 95
@since ― 2.0.0
tap(() => 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const annotateCurrentSpan: (key: string, value: unknown) => Effect.Effect<void> (+1 overload)
Adds annotations to the currently active span for traceability.
Details
This function adds key-value annotations to the currently active span in the
effect's trace. These annotations help provide more context about the
operation being executed at a specific point in time. Unlike
annotateSpans
, which applies to all spans in an effect, this function
focuses solely on the active span.
You can either pass a single key-value pair or a record of key-value pairs to
annotate the span. These annotations are useful for adding metadata to
operations, especially in systems with detailed observability requirements.
@since ― 2.0.0
annotateCurrentSpan("key", "value")),
12
  // Wrap the effect in a span named 'myspan'
13
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const withSpan: (name: string, options?: SpanOptions | undefined) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, ParentSpan>> (+1 overload)
Wraps the effect with a new span for tracing.
@since ― 2.0.0
withSpan("myspan")
14
)
15

16
// Set up tracing with the OpenTelemetry SDK
17
const 
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive = 
import NodeSdk
NodeSdk.
const layer: (evaluate: LazyArg<NodeSdk.Configuration>) => Layer<Resource> (+1 overload)@since ― 1.0.0
layer(() => ({
18
  
Configuration.resource?: {
    readonly serviceName: string;
    readonly serviceVersion?: string;
    readonly attributes?: ResourceAttributes;
} | undefined
resource: { 
serviceName: string
serviceName: "example" },
19
  
Configuration.spanProcessor?: SpanProcessor | readonly SpanProcessor[] | undefined
spanProcessor: new 
new BatchSpanProcessor<BufferConfig>(_exporter: SpanExporter, config?: BufferConfig | undefined): BatchSpanProcessor
BatchSpanProcessor(new 
new ConsoleSpanExporter(): ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter())
20
}))
21

22
// Run the effect, providing the tracing layer
23
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const runPromise: <void, never>(effect: Effect.Effect<void, never, never>, options?: {
    readonly signal?: AbortSignal;
} | undefined) => Promise<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.
@see ― runPromiseExit for a version that returns an Exit type instead
of rejecting.
@example 
// Title: Running a Successful Effect as a Promise
import { Effect } from "effect"

// Effect.runPromise(Effect.succeed(1)).then(console.log)
// Output: 1
@example 
//Example: Handling a Failing Effect as a Rejected Promise
import { Effect } from "effect"
// Effect.runPromise(Effect.fail("my error")).catch(console.error)
// Output:
// (FiberFailure) Error: my error
@since ― 2.0.0
runPromise(
const program: Effect.Effect<void, never, never>
program.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const provide: <Resource, never, never>(layer: Layer<Resource, never, never>) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, Resource>> (+9 overloads)
Provides necessary dependencies to an effect, removing its environmental
requirements.
Details
This function allows you to supply the required environment for an effect.
The environment can be provided in the form of one or more Layers, a
Context, a Runtime, or a ManagedRuntime. Once the environment is
provided, the effect can run without requiring external dependencies.
You can compose layers to create a modular and reusable way of setting up the
environment for effects. For example, layers can be used to configure
databases, logging services, or any other required dependencies.
@see ― provideService for providing a service to an effect.
@example 
import { Context, Effect, Layer } from "effect"

class Database extends Context.Tag("Database")<
  Database,
  { readonly query: (sql: string) => Effect.Effect<Array<unknown>> }
>() {}

const DatabaseLive = Layer.succeed(
  Database,
  {
    // Simulate a database query
    query: (sql: string) => Effect.log(`Executing query: ${sql}`).pipe(Effect.as([]))
  }
)

//      ┌─── Effect<unknown[], never, Database>
//      ▼
const program = Effect.gen(function*() {
  const database = yield* Database
  const result = yield* database.query("SELECT * FROM users")
  return result
})

//      ┌─── Effect<unknown[], never, never>
//      ▼
const runnable = Effect.provide(program, DatabaseLive)

// Effect.runPromise(runnable).then(console.log)
// Output:
// timestamp=... level=INFO fiber=#0 message="Executing query: SELECT * FROM users"
// []
@since ― 2.0.0
provide(
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive)))
24
/*
25
Example Output:
26
{
27
  resource: {
28
    attributes: {
29
      'service.name': 'example',
30
      'telemetry.sdk.language': 'nodejs',
31
      'telemetry.sdk.name': '@effect/opentelemetry',
32
      'telemetry.sdk.version': '1.28.0'
33
    }
34
  },
35
  instrumentationScope: { name: 'example', version: undefined, schemaUrl: undefined },
36
  traceId: 'c8120e01c0f1ea83ccc1d388e5cdebd3',
37
  parentId: undefined,
38
  traceState: undefined,
39
  name: 'myspan',
40
  id: '81c430ba4979f1db',
41
  kind: 0,
42
  timestamp: 1733220874356084,
43
  duration: 102821.417,
44
  attributes: { key: 'value' },
45
  status: { code: 1 },
46
  events: [],
47
  links: []
48
}
49
*/

Logs as events

In the context of tracing, logs are converted into “Span Events.” These events offer structured insights into your application’s activities and provide a timeline of when specific operations occurred.

1
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
2
import { 
import NodeSdk
NodeSdk } from "@effect/opentelemetry"
3
import {
4
  
class ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter,
5
  
class BatchSpanProcessor
BatchSpanProcessor
6
} from "@opentelemetry/sdk-trace-base"
7

8
// Define a program that logs a message and delays for 100 milliseconds
9
const 
const program: Effect.Effect<void, never, never>
program = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const log: (...message: ReadonlyArray<any>) => Effect.Effect<void, never, never>
Logs one or more messages or error causes at the current log level.
Details
This function provides a simple way to log messages or error causes during
the execution of your effects. By default, logs are recorded at the INFO
level, but this can be adjusted using other logging utilities
(Logger.withMinimumLogLevel). Multiple items, including Cause instances,
can be logged in a single call. When logging Cause instances, detailed
error information is included in the log output.
The log output includes useful metadata like the current timestamp, log
level, and fiber ID, making it suitable for debugging and tracking purposes.
This function does not interrupt or alter the effect's execution flow.
@example 
import { Cause, Effect } from "effect"

const program = Effect.log(
  "message1",
  "message2",
  Cause.die("Oh no!"),
  Cause.die("Oh uh!")
)

// Effect.runFork(program)
// Output:
// timestamp=... level=INFO fiber=#0 message=message1 message=message2 cause="Error: Oh no!
// Error: Oh uh!"
@since ― 2.0.0
log("Hello").
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<...>, bc: (_: Effect.Effect<...>) => Effect.Effect<...>): Effect.Effect<...> (+21 overloads)
pipe(
10
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const delay: (duration: DurationInput) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R> (+1 overload)
Delays the execution of an effect by a specified Duration.
**Details
This function postpones the execution of the provided effect by the specified
duration. The duration can be provided in various formats supported by the
Duration module.
Internally, this function does not block the thread; instead, it uses an
efficient, non-blocking mechanism to introduce the delay.
@example 
import { Console, Effect } from "effect"

const task = Console.log("Task executed")

const program = Console.log("start").pipe(
  Effect.andThen(
    // Delays the log message by 2 seconds
    task.pipe(Effect.delay("2 seconds"))
  )
)

// Effect.runFork(program)
// Output:
// start
// Task executed
@since ― 2.0.0
delay("100 millis"),
11
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const withSpan: (name: string, options?: SpanOptions | undefined) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, ParentSpan>> (+1 overload)
Wraps the effect with a new span for tracing.
@since ― 2.0.0
withSpan("myspan")
12
)
13

14
// Set up tracing with the OpenTelemetry SDK
15
const 
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive = 
import NodeSdk
NodeSdk.
const layer: (evaluate: LazyArg<NodeSdk.Configuration>) => Layer<Resource> (+1 overload)@since ― 1.0.0
layer(() => ({
16
  
Configuration.resource?: {
    readonly serviceName: string;
    readonly serviceVersion?: string;
    readonly attributes?: ResourceAttributes;
} | undefined
resource: { 
serviceName: string
serviceName: "example" },
17
  
Configuration.spanProcessor?: SpanProcessor | readonly SpanProcessor[] | undefined
spanProcessor: new 
new BatchSpanProcessor<BufferConfig>(_exporter: SpanExporter, config?: BufferConfig | undefined): BatchSpanProcessor
BatchSpanProcessor(new 
new ConsoleSpanExporter(): ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter())
18
}))
19

20
// Run the effect, providing the tracing layer
21
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const runPromise: <void, never>(effect: Effect.Effect<void, never, never>, options?: {
    readonly signal?: AbortSignal;
} | undefined) => Promise<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.
@see ― runPromiseExit for a version that returns an Exit type instead
of rejecting.
@example 
// Title: Running a Successful Effect as a Promise
import { Effect } from "effect"

// Effect.runPromise(Effect.succeed(1)).then(console.log)
// Output: 1
@example 
//Example: Handling a Failing Effect as a Rejected Promise
import { Effect } from "effect"
// Effect.runPromise(Effect.fail("my error")).catch(console.error)
// Output:
// (FiberFailure) Error: my error
@since ― 2.0.0
runPromise(
const program: Effect.Effect<void, never, never>
program.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const provide: <Resource, never, never>(layer: Layer<Resource, never, never>) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, Resource>> (+9 overloads)
Provides necessary dependencies to an effect, removing its environmental
requirements.
Details
This function allows you to supply the required environment for an effect.
The environment can be provided in the form of one or more Layers, a
Context, a Runtime, or a ManagedRuntime. Once the environment is
provided, the effect can run without requiring external dependencies.
You can compose layers to create a modular and reusable way of setting up the
environment for effects. For example, layers can be used to configure
databases, logging services, or any other required dependencies.
@see ― provideService for providing a service to an effect.
@example 
import { Context, Effect, Layer } from "effect"

class Database extends Context.Tag("Database")<
  Database,
  { readonly query: (sql: string) => Effect.Effect<Array<unknown>> }
>() {}

const DatabaseLive = Layer.succeed(
  Database,
  {
    // Simulate a database query
    query: (sql: string) => Effect.log(`Executing query: ${sql}`).pipe(Effect.as([]))
  }
)

//      ┌─── Effect<unknown[], never, Database>
//      ▼
const program = Effect.gen(function*() {
  const database = yield* Database
  const result = yield* database.query("SELECT * FROM users")
  return result
})

//      ┌─── Effect<unknown[], never, never>
//      ▼
const runnable = Effect.provide(program, DatabaseLive)

// Effect.runPromise(runnable).then(console.log)
// Output:
// timestamp=... level=INFO fiber=#0 message="Executing query: SELECT * FROM users"
// []
@since ― 2.0.0
provide(
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive)))
22
/*
23
Example Output:
24
{
25
  resource: {
26
    attributes: {
27
      'service.name': 'example',
28
      'telemetry.sdk.language': 'nodejs',
29
      'telemetry.sdk.name': '@effect/opentelemetry',
30
      'telemetry.sdk.version': '1.28.0'
31
    }
32
  },
33
  instrumentationScope: { name: 'example', version: undefined, schemaUrl: undefined },
34
  traceId: 'b0f4f012b5b13c0a040f7002a1d7b020',
35
  parentId: undefined,
36
  traceState: undefined,
37
  name: 'myspan',
38
  id: 'b9ba8472002715a8',
39
  kind: 0,
40
  timestamp: 1733220905504162.2,
41
  duration: 103790,
42
  attributes: {},
43
  status: { code: 1 },
44
  events: [
45
    {
46
      name: 'Hello',
47
      attributes: { 'effect.fiberId': '#0', 'effect.logLevel': 'INFO' }, // Log attributes
48
      time: [ 1733220905, 607761042 ], // Event timestamp
49
      droppedAttributesCount: 0
50
    }
51
  ],
52
  links: []
53
}
54
*/

Each span can include events, which capture specific moments during the execution of a span. In this example, a log message "Hello" is recorded as an event within the span. Key details of the event include:

Field	Description
`name`	The name of the event, which corresponds to the logged message (e.g., `'Hello'`).
`attributes`	Key-value pairs that provide additional context about the event, such as `fiberId` and log level.
`time`	The timestamp of when the event occurred, shown in a high-precision format.
`droppedAttributesCount`	Indicates how many attributes were discarded, if any. In this case, no attributes were dropped.

Nesting Spans

Spans can be nested to represent a hierarchy of operations. This allows you to track how different parts of your application relate to one another during execution. The following example demonstrates how to create and manage nested spans.

Example (Nesting Spans in a Trace)

1
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
2
import { 
import NodeSdk
NodeSdk } from "@effect/opentelemetry"
3
import {
4
  
class ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter,
5
  
class BatchSpanProcessor
BatchSpanProcessor
6
} from "@opentelemetry/sdk-trace-base"
7

8
const 
const child: Effect.Effect<void, never, never>
child = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const void: Effect.Effect<void, never, never>
export void
Represents an effect that does nothing and produces no value.
When to Use
Use this effect when you need to represent an effect that does nothing.
This is useful in scenarios where you need to satisfy an effect-based
interface or control program flow without performing any operations. For
example, it can be used in situations where you want to return an effect
from a function but do not need to compute or return any result.
@since ― 2.0.0
void.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<...>, bc: (_: Effect.Effect<...>) => Effect.Effect<...>): Effect.Effect<...> (+21 overloads)
pipe(
9
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const delay: (duration: DurationInput) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R> (+1 overload)
Delays the execution of an effect by a specified Duration.
**Details
This function postpones the execution of the provided effect by the specified
duration. The duration can be provided in various formats supported by the
Duration module.
Internally, this function does not block the thread; instead, it uses an
efficient, non-blocking mechanism to introduce the delay.
@example 
import { Console, Effect } from "effect"

const task = Console.log("Task executed")

const program = Console.log("start").pipe(
  Effect.andThen(
    // Delays the log message by 2 seconds
    task.pipe(Effect.delay("2 seconds"))
  )
)

// Effect.runFork(program)
// Output:
// start
// Task executed
@since ― 2.0.0
delay("100 millis"),
10
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const withSpan: (name: string, options?: SpanOptions | undefined) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, ParentSpan>> (+1 overload)
Wraps the effect with a new span for tracing.
@since ― 2.0.0
withSpan("child")
11
)
12

13
const 
const parent: Effect.Effect<void, never, never>
parent = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const gen: <YieldWrap<Effect.Effect<void, never, never>>, void>(f: (resume: Effect.Adapter) => Generator<YieldWrap<Effect.Effect<void, never, never>>, void, never>) => Effect.Effect<...> (+1 overload)
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
@example 
import { Effect } from "effect"

const addServiceCharge = (amount: number) => amount + 1

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)

const fetchTransactionAmount = Effect.promise(() => Promise.resolve(100))

const fetchDiscountRate = Effect.promise(() => Promise.resolve(5))

export const program = Effect.gen(function* () {
  const transactionAmount = yield* fetchTransactionAmount
  const discountRate = yield* fetchDiscountRate
  const discountedAmount = yield* applyDiscount(
    transactionAmount,
    discountRate
  )
  const finalAmount = addServiceCharge(discountedAmount)
  return `Final amount to charge: ${finalAmount}`
})
@since ― 2.0.0
gen(function* () {
14
  yield* 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const sleep: (duration: DurationInput) => Effect.Effect<void>
Suspends the execution of an effect for a specified Duration.
Details
This function pauses the execution of an effect for a given duration. It is
asynchronous, meaning that it does not block the fiber executing the effect.
Instead, the fiber is suspended during the delay period and can resume once
the specified time has passed.
The duration can be specified using various formats supported by the
Duration module, such as a string ("2 seconds") or numeric value
representing milliseconds.
@example 
import { Effect } from "effect"

const program = Effect.gen(function*() {
  console.log("Starting task...")
  yield* Effect.sleep("3 seconds") // Waits for 3 seconds
  console.log("Task completed!")
})

// Effect.runFork(program)
// Output:
// Starting task...
// Task completed!
@since ― 2.0.0
sleep("20 millis")
15
  yield* 
const child: Effect.Effect<void, never, never>
child
16
  yield* 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const sleep: (duration: DurationInput) => Effect.Effect<void>
Suspends the execution of an effect for a specified Duration.
Details
This function pauses the execution of an effect for a given duration. It is
asynchronous, meaning that it does not block the fiber executing the effect.
Instead, the fiber is suspended during the delay period and can resume once
the specified time has passed.
The duration can be specified using various formats supported by the
Duration module, such as a string ("2 seconds") or numeric value
representing milliseconds.
@example 
import { Effect } from "effect"

const program = Effect.gen(function*() {
  console.log("Starting task...")
  yield* Effect.sleep("3 seconds") // Waits for 3 seconds
  console.log("Task completed!")
})

// Effect.runFork(program)
// Output:
// Starting task...
// Task completed!
@since ― 2.0.0
sleep("10 millis")
17
}).
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const withSpan: (name: string, options?: SpanOptions | undefined) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, ParentSpan>> (+1 overload)
Wraps the effect with a new span for tracing.
@since ― 2.0.0
withSpan("parent"))
18

19
// Set up tracing with the OpenTelemetry SDK
20
const 
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive = 
import NodeSdk
NodeSdk.
const layer: (evaluate: LazyArg<NodeSdk.Configuration>) => Layer<Resource> (+1 overload)@since ― 1.0.0
layer(() => ({
21
  
Configuration.resource?: {
    readonly serviceName: string;
    readonly serviceVersion?: string;
    readonly attributes?: ResourceAttributes;
} | undefined
resource: { 
serviceName: string
serviceName: "example" },
22
  
Configuration.spanProcessor?: SpanProcessor | readonly SpanProcessor[] | undefined
spanProcessor: new 
new BatchSpanProcessor<BufferConfig>(_exporter: SpanExporter, config?: BufferConfig | undefined): BatchSpanProcessor
BatchSpanProcessor(new 
new ConsoleSpanExporter(): ConsoleSpanExporter
This is implementation of
SpanExporter
that prints spans to the
console. This class can be used for diagnostic purposes.
NOTE: This
SpanExporter
is intended for diagnostics use only, output rendered to the console may change at any time.
ConsoleSpanExporter())
23
}))
24

25
// Run the effect, providing the tracing layer
26
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const runPromise: <void, never>(effect: Effect.Effect<void, never, never>, options?: {
    readonly signal?: AbortSignal;
} | undefined) => Promise<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.
@see ― runPromiseExit for a version that returns an Exit type instead
of rejecting.
@example 
// Title: Running a Successful Effect as a Promise
import { Effect } from "effect"

// Effect.runPromise(Effect.succeed(1)).then(console.log)
// Output: 1
@example 
//Example: Handling a Failing Effect as a Rejected Promise
import { Effect } from "effect"
// Effect.runPromise(Effect.fail("my error")).catch(console.error)
// Output:
// (FiberFailure) Error: my error
@since ― 2.0.0
runPromise(
const parent: Effect.Effect<void, never, never>
parent.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const provide: <Resource, never, never>(layer: Layer<Resource, never, never>) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, Resource>> (+9 overloads)
Provides necessary dependencies to an effect, removing its environmental
requirements.
Details
This function allows you to supply the required environment for an effect.
The environment can be provided in the form of one or more Layers, a
Context, a Runtime, or a ManagedRuntime. Once the environment is
provided, the effect can run without requiring external dependencies.
You can compose layers to create a modular and reusable way of setting up the
environment for effects. For example, layers can be used to configure
databases, logging services, or any other required dependencies.
@see ― provideService for providing a service to an effect.
@example 
import { Context, Effect, Layer } from "effect"

class Database extends Context.Tag("Database")<
  Database,
  { readonly query: (sql: string) => Effect.Effect<Array<unknown>> }
>() {}

const DatabaseLive = Layer.succeed(
  Database,
  {
    // Simulate a database query
    query: (sql: string) => Effect.log(`Executing query: ${sql}`).pipe(Effect.as([]))
  }
)

//      ┌─── Effect<unknown[], never, Database>
//      ▼
const program = Effect.gen(function*() {
  const database = yield* Database
  const result = yield* database.query("SELECT * FROM users")
  return result
})

//      ┌─── Effect<unknown[], never, never>
//      ▼
const runnable = Effect.provide(program, DatabaseLive)

// Effect.runPromise(runnable).then(console.log)
// Output:
// timestamp=... level=INFO fiber=#0 message="Executing query: SELECT * FROM users"
// []
@since ― 2.0.0
provide(
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive)))
27
/*
28
Example Output:
29
{
30
  resource: {
31
    attributes: {
32
      'service.name': 'example',
33
      'telemetry.sdk.language': 'nodejs',
34
      'telemetry.sdk.name': '@effect/opentelemetry',
35
      'telemetry.sdk.version': '1.28.0'
36
    }
37
  },
38
  instrumentationScope: { name: 'example', version: undefined, schemaUrl: undefined },
39
  traceId: 'a9cd69ad70698a0c7b7b774597c77d39',
40
  parentId: 'a09e5c3fdfdbbc1d', // This indicates the span is a child of 'parent'
41
  traceState: undefined,
42
  name: 'child',
43
  id: '210d2f9b648389a4', // Unique ID for the child span
44
  kind: 0,
45
  timestamp: 1733220970590126.2,
46
  duration: 101579.875,
47
  attributes: {},
48
  status: { code: 1 },
49
  events: [],
50
  links: []
51
}
52
{
53
  resource: {
54
    attributes: {
55
      'service.name': 'example',
56
      'telemetry.sdk.language': 'nodejs',
57
      'telemetry.sdk.name': '@effect/opentelemetry',
58
      'telemetry.sdk.version': '1.28.0'
59
    }
60
  },
61
  instrumentationScope: { name: 'example', version: undefined, schemaUrl: undefined },
62
  traceId: 'a9cd69ad70698a0c7b7b774597c77d39',
63
  parentId: undefined, // Indicates this is the root span
64
  traceState: undefined,
65
  name: 'parent',
66
  id: 'a09e5c3fdfdbbc1d', // Unique ID for the parent span
67
  kind: 0,
68
  timestamp: 1733220970569015.2,
69
  duration: 132612.208,
70
  attributes: {},
71
  status: { code: 1 },
72
  events: [],
73
  links: []
74
}
75
*/

The parent-child relationship is evident in the span output, where the parentId of the child span matches the id of the parent span. This structure helps track how operations are related within a single trace.

Tutorial: Visualizing Traces with Docker, Prometheus, Grafana, and Tempo

In this tutorial, we’ll guide you through simulating and visualizing traces using a sample instrumented Node.js application. We will use Docker, Prometheus, Grafana, and Tempo to create, collect, and visualize traces.

Tools Explained

Let’s understand the tools we’ll be using in simple terms:

Docker: Docker allows us to run applications in containers. Think of a container as a lightweight and isolated environment where your application can run consistently, regardless of the host system. It’s a bit like a virtual machine but more efficient.
Prometheus: Prometheus is a monitoring and alerting toolkit. It collects metrics and data about your applications and stores them for further analysis. This helps in identifying performance issues and understanding the behavior of your applications.
Grafana: Grafana is a visualization and analytics platform. It helps in creating beautiful and interactive dashboards to visualize your application’s data. You can use it to graphically represent metrics collected by Prometheus.
Tempo: Tempo is a distributed tracing system that allows you to trace the journey of a request as it flows through your application. It provides insights into how requests are processed and helps in debugging and optimizing your applications.

Getting Docker

To get Docker, follow these steps:

Visit the Docker website at https://www.docker.com/.
Download Docker Desktop for your operating system (Windows or macOS) and install it.
After installation, open Docker Desktop, and it will run in the background.

Simulating Traces

Now, let’s simulate traces using a sample Node.js application. We’ll provide you with the code and guide you on setting up the necessary components.

Download Docker Files. Download the required Docker files: docker.zip
Set Up docker. Unzip the downloaded file, navigate to the /docker/local directory in your terminal or command prompt and run the following command to start the necessary services:
Terminal window
```
docker-compose up
```

Simulate Traces. Run the following example code in your Node.js environment. This code simulates a set of tasks and generates traces.

Before proceeding, you’ll need to install additional libraries in addition to the latest version of effect. Here are the required libraries:

npm install @effect/opentelemetry
npm install @opentelemetry/exporter-trace-otlp-http
npm install @opentelemetry/sdk-trace-base
npm install @opentelemetry/sdk-trace-web
npm install @opentelemetry/sdk-trace-node

pnpm add @effect/opentelemetry
pnpm add @opentelemetry/exporter-trace-otlp-http
pnpm add @opentelemetry/sdk-trace-base
# For NodeJS applications
pnpm add @opentelemetry/sdk-trace-node
# For browser applications
pnpm add @opentelemetry/sdk-trace-web
# If you also need to export metrics
pnpm add @opentelemetry/sdk-metrics

yarn add @effect/opentelemetry
yarn add @opentelemetry/exporter-trace-otlp-http
yarn add @opentelemetry/sdk-trace-base
# For NodeJS applications
yarn add @opentelemetry/sdk-trace-node
# For browser applications
yarn add @opentelemetry/sdk-trace-web
# If you also need to export metrics
yarn add @opentelemetry/sdk-metrics

bun add @effect/opentelemetry
bun add @opentelemetry/exporter-trace-otlp-http
bun add @opentelemetry/sdk-trace-base
# For NodeJS applications
bun add @opentelemetry/sdk-trace-node
# For browser applications
bun add @opentelemetry/sdk-trace-web
# If you also need to export metrics
bun add @opentelemetry/sdk-metrics

1
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
2
import { 
import NodeSdk
NodeSdk } from "@effect/opentelemetry"
3
import { 
class BatchSpanProcessor
BatchSpanProcessor } from "@opentelemetry/sdk-trace-base"
4
import { 
class OTLPTraceExporter
Collector Trace Exporter for Node
OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-http"
5

6
// Function to simulate a task with possible subtasks
7
const 
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task = (
8
  
name: string
name: string,
9
  
delay: number
delay: number,
10
  
children: readonly Effect.Effect<void, never, never>[]
children: 
interface ReadonlyArray<T>
ReadonlyArray<
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
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.
@since ― 2.0.0
@since ― 2.0.0
Effect<void>> = []
11
) =>
12
  
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const gen: <YieldWrap<Effect.Effect<void, never, never>>, void>(f: (resume: Effect.Adapter) => Generator<YieldWrap<Effect.Effect<void, never, never>>, void, never>) => Effect.Effect<...> (+1 overload)
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
@example 
import { Effect } from "effect"

const addServiceCharge = (amount: number) => amount + 1

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)

const fetchTransactionAmount = Effect.promise(() => Promise.resolve(100))

const fetchDiscountRate = Effect.promise(() => Promise.resolve(5))

export const program = Effect.gen(function* () {
  const transactionAmount = yield* fetchTransactionAmount
  const discountRate = yield* fetchDiscountRate
  const discountedAmount = yield* applyDiscount(
    transactionAmount,
    discountRate
  )
  const finalAmount = addServiceCharge(discountedAmount)
  return `Final amount to charge: ${finalAmount}`
})
@since ― 2.0.0
gen(function* () {
13
    yield* 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const log: (...message: ReadonlyArray<any>) => Effect.Effect<void, never, never>
Logs one or more messages or error causes at the current log level.
Details
This function provides a simple way to log messages or error causes during
the execution of your effects. By default, logs are recorded at the INFO
level, but this can be adjusted using other logging utilities
(Logger.withMinimumLogLevel). Multiple items, including Cause instances,
can be logged in a single call. When logging Cause instances, detailed
error information is included in the log output.
The log output includes useful metadata like the current timestamp, log
level, and fiber ID, making it suitable for debugging and tracking purposes.
This function does not interrupt or alter the effect's execution flow.
@example 
import { Cause, Effect } from "effect"

const program = Effect.log(
  "message1",
  "message2",
  Cause.die("Oh no!"),
  Cause.die("Oh uh!")
)

// Effect.runFork(program)
// Output:
// timestamp=... level=INFO fiber=#0 message=message1 message=message2 cause="Error: Oh no!
// Error: Oh uh!"
@since ― 2.0.0
log(
name: string
name)
14
    yield* 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const sleep: (duration: DurationInput) => Effect.Effect<void>
Suspends the execution of an effect for a specified Duration.
Details
This function pauses the execution of an effect for a given duration. It is
asynchronous, meaning that it does not block the fiber executing the effect.
Instead, the fiber is suspended during the delay period and can resume once
the specified time has passed.
The duration can be specified using various formats supported by the
Duration module, such as a string ("2 seconds") or numeric value
representing milliseconds.
@example 
import { Effect } from "effect"

const program = Effect.gen(function*() {
  console.log("Starting task...")
  yield* Effect.sleep("3 seconds") // Waits for 3 seconds
  console.log("Task completed!")
})

// Effect.runFork(program)
// Output:
// Starting task...
// Task completed!
@since ― 2.0.0
sleep(`${
delay: number
delay} millis`)
15
    for (const 
const child: Effect.Effect<void, never, never>
child of 
children: readonly Effect.Effect<void, never, never>[]
children) {
16
      yield* 
const child: Effect.Effect<void, never, never>
child
17
    }
18
    yield* 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const sleep: (duration: DurationInput) => Effect.Effect<void>
Suspends the execution of an effect for a specified Duration.
Details
This function pauses the execution of an effect for a given duration. It is
asynchronous, meaning that it does not block the fiber executing the effect.
Instead, the fiber is suspended during the delay period and can resume once
the specified time has passed.
The duration can be specified using various formats supported by the
Duration module, such as a string ("2 seconds") or numeric value
representing milliseconds.
@example 
import { Effect } from "effect"

const program = Effect.gen(function*() {
  console.log("Starting task...")
  yield* Effect.sleep("3 seconds") // Waits for 3 seconds
  console.log("Task completed!")
})

// Effect.runFork(program)
// Output:
// Starting task...
// Task completed!
@since ― 2.0.0
sleep(`${
delay: number
delay} millis`)
19
  }).
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<void, never, never>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const withSpan: (name: string, options?: SpanOptions | undefined) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, ParentSpan>> (+1 overload)
Wraps the effect with a new span for tracing.
@since ― 2.0.0
withSpan(
name: string
name))
20

21
const 
const poll: Effect.Effect<void, never, never>
poll = 
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("/poll", 1)
22

23
// Create a program with tasks and subtasks
24
const 
const program: Effect.Effect<void, never, never>
program = 
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("client", 2, [
25
  
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("/api", 3, [
26
    
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("/authN", 4, [
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("/authZ", 5)]),
27
    
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("/payment Gateway", 6, [
28
      
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("DB", 7),
29
      
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("Ext. Merchant", 8)
30
    ]),
31
    
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("/dispatch", 9, [
32
      
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("/dispatch/search", 10),
33
      
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const all: <readonly [Effect.Effect<void, never, never>, Effect.Effect<void, never, never>, Effect.Effect<void, never, never>], {
    concurrency: "inherit";
}>(arg: readonly [Effect.Effect<void, never, never>, Effect.Effect<...>, Effect.Effect<...>], options?: {
    concurrency: "inherit";
} | undefined) => Effect.Effect<...>
Combines multiple effects into one, returning results based on the input
structure.
Details
Use this function when you need to run multiple effects and combine their
results into a single output. It supports tuples, iterables, structs, and
records, making it flexible for different input types.
For instance, if the input is a tuple:
//         ┌─── a tuple of effects
//         ▼
Effect.all([effect1, effect2, ...])
the effects are executed sequentially, and the result is a new effect
containing the results as a tuple. The results in the tuple match the order
of the effects passed to Effect.all.
Concurrency
You can control the execution order (e.g., sequential vs. concurrent) using
the concurrency option.
Short-Circuiting Behavior
This function stops execution on the first error it encounters, this is
called "short-circuiting". If any effect in the collection fails, the
remaining effects will not run, and the error will be propagated. To change
this behavior, you can use the mode option, which allows all effects to run
and collect results as Either or Option.
The mode option
The { mode: "either" } option changes the behavior of Effect.all to
ensure all effects run, even if some fail. Instead of stopping on the first
failure, this mode collects both successes and failures, returning an array
of Either instances where each result is either a Right (success) or a
Left (failure).
Similarly, the { mode: "validate" } option uses Option to indicate
success or failure. Each effect returns None for success and Some with
the error for failure.
@see ― forEach for iterating over elements and applying an effect.
@see ― allWith for a data-last version of this function.
@example 
// Title: Combining Effects in Tuples
import { Effect, Console } from "effect"

const tupleOfEffects = [
  Effect.succeed(42).pipe(Effect.tap(Console.log)),
  Effect.succeed("Hello").pipe(Effect.tap(Console.log))
] as const

//      ┌─── Effect<[number, string], never, never>
//      ▼
const resultsAsTuple = Effect.all(tupleOfEffects)

// Effect.runPromise(resultsAsTuple).then(console.log)
// Output:
// 42
// Hello
// [ 42, 'Hello' ]
@example 
// Title: Combining Effects in Iterables
import { Effect, Console } from "effect"
const iterableOfEffects: Iterable<Effect.Effect> = [1, 2, 3].map(
(n) => Effect.succeed(n).pipe(Effect.tap(Console.log))
)
//      ┌─── Effect<number[], never, never>
//      ▼
const resultsAsArray = Effect.all(iterableOfEffects)
// Effect.runPromise(resultsAsArray).then(console.log)
// Output:
// 1
// 2
// 3
// [ 1, 2, 3 ]
@example 
// Title: Combining Effects in Structs
import { Effect, Console } from "effect"
const structOfEffects = {
a: Effect.succeed(42).pipe(Effect.tap(Console.log)),
b: Effect.succeed("Hello").pipe(Effect.tap(Console.log))
}
//      ┌─── Effect<{ a: number; b: string; }, never, never>
//      ▼
const resultsAsStruct = Effect.all(structOfEffects)
// Effect.runPromise(resultsAsStruct).then(console.log)
// Output:
// 42
// Hello
// { a: 42, b: 'Hello' }
@example 
// Title: Combining Effects in Records
import { Effect, Console } from "effect"
const recordOfEffects: Record<string, Effect.Effect> = {
key1: Effect.succeed(1).pipe(Effect.tap(Console.log)),
key2: Effect.succeed(2).pipe(Effect.tap(Console.log))
}
//      ┌─── Effect<{ [x: string]: number; }, never, never>
//      ▼
const resultsAsRecord = Effect.all(recordOfEffects)
// Effect.runPromise(resultsAsRecord).then(console.log)
// Output:
// 1
// 2
// { key1: 1, key2: 2 }
@example 
// Title: Short-Circuiting Behavior
import { Effect, Console } from "effect"
const program = Effect.all([
Effect.succeed("Task1").pipe(Effect.tap(Console.log)),
Effect.fail("Task2: Oh no!").pipe(Effect.tap(Console.log)),
// Won't execute due to earlier failure
Effect.succeed("Task3").pipe(Effect.tap(Console.log))
])
// Effect.runPromiseExit(program).then(console.log)
// Output:
// Task1
// {
//   _id: 'Exit',
//   _tag: 'Failure',
//   cause: { _id: 'Cause', _tag: 'Fail', failure: 'Task2: Oh no!' }
// }
@example 
// Title: Collecting Results with mode: "either"
import { Effect, Console } from "effect"
const effects = [
Effect.succeed("Task1").pipe(Effect.tap(Console.log)),
Effect.fail("Task2: Oh no!").pipe(Effect.tap(Console.log)),
Effect.succeed("Task3").pipe(Effect.tap(Console.log))
]
const program = Effect.all(effects, { mode: "either" })
// Effect.runPromiseExit(program).then(console.log)
// Output:
// Task1
// Task3
// {
//   _id: 'Exit',
//   _tag: 'Success',
//   value: [
//     { _id: 'Either', _tag: 'Right', right: 'Task1' },
//     { _id: 'Either', _tag: 'Left', left: 'Task2: Oh no!' },
//     { _id: 'Either', _tag: 'Right', right: 'Task3' }
//   ]
// }
@example 
//Example: Collecting Results with mode: "validate"
import { Effect, Console } from "effect"
const effects = [
Effect.succeed("Task1").pipe(Effect.tap(Console.log)),
Effect.fail("Task2: Oh no!").pipe(Effect.tap(Console.log)),
Effect.succeed("Task3").pipe(Effect.tap(Console.log))
]
const program = Effect.all(effects, { mode: "validate" })
// Effect.runPromiseExit(program).then((result) => console.log("%o", result))
// Output:
// Task1
// Task3
// {
//   _id: 'Exit',
//   _tag: 'Failure',
//   cause: {
//     _id: 'Cause',
//     _tag: 'Fail',
//     failure: [
//       { _id: 'Option', _tag: 'None' },
//       { _id: 'Option', _tag: 'Some', value: 'Task2: Oh no!' },
//       { _id: 'Option', _tag: 'None' }
//     ]
//   }
// }
@since ― 2.0.0
all([
const poll: Effect.Effect<void, never, never>
poll, 
const poll: Effect.Effect<void, never, never>
poll, 
const poll: Effect.Effect<void, never, never>
poll], { 
concurrency: "inherit"
concurrency: "inherit" }),
34
      
const task: (name: string, delay: number, children?: ReadonlyArray<Effect.Effect<void>>) => Effect.Effect<void, never, never>
task("/pollDriver/{id}", 11)
35
    ])
36
  ])
37
])
38

39
const 
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive = 
import NodeSdk
NodeSdk.
const layer: (evaluate: LazyArg<NodeSdk.Configuration>) => Layer<Resource> (+1 overload)@since ― 1.0.0
layer(() => ({
40
  
Configuration.resource?: {
    readonly serviceName: string;
    readonly serviceVersion?: string;
    readonly attributes?: ResourceAttributes;
} | undefined
resource: { 
serviceName: string
serviceName: "example" },
41
  
Configuration.spanProcessor?: SpanProcessor | readonly SpanProcessor[] | undefined
spanProcessor: new 
new BatchSpanProcessor<BufferConfig>(_exporter: SpanExporter, config?: BufferConfig | undefined): BatchSpanProcessor
BatchSpanProcessor(new 
new OTLPTraceExporter(config?: OTLPExporterNodeConfigBase): OTLPTraceExporter
Collector Trace Exporter for Node
OTLPTraceExporter())
42
}))
43

44
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const runPromise: <void, never>(effect: Effect.Effect<void, never, never>, options?: {
    readonly signal?: AbortSignal;
} | undefined) => Promise<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.
@see ― runPromiseExit for a version that returns an Exit type instead
of rejecting.
@example 
// Title: Running a Successful Effect as a Promise
import { Effect } from "effect"

// Effect.runPromise(Effect.succeed(1)).then(console.log)
// Output: 1
@example 
//Example: Handling a Failing Effect as a Rejected Promise
import { Effect } from "effect"
// Effect.runPromise(Effect.fail("my error")).catch(console.error)
// Output:
// (FiberFailure) Error: my error
@since ― 2.0.0
runPromise(
45
  
const program: Effect.Effect<void, never, never>
program.
Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<void, never, never>, Effect.Effect<void, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<...>, bc: (_: Effect.Effect<...>) => Effect.Effect<...>): Effect.Effect<...> (+21 overloads)
pipe(
46
    
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const provide: <Resource, never, never>(layer: Layer<Resource, never, never>) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, Resource>> (+9 overloads)
Provides necessary dependencies to an effect, removing its environmental
requirements.
Details
This function allows you to supply the required environment for an effect.
The environment can be provided in the form of one or more Layers, a
Context, a Runtime, or a ManagedRuntime. Once the environment is
provided, the effect can run without requiring external dependencies.
You can compose layers to create a modular and reusable way of setting up the
environment for effects. For example, layers can be used to configure
databases, logging services, or any other required dependencies.
@see ― provideService for providing a service to an effect.
@example 
import { Context, Effect, Layer } from "effect"

class Database extends Context.Tag("Database")<
  Database,
  { readonly query: (sql: string) => Effect.Effect<Array<unknown>> }
>() {}

const DatabaseLive = Layer.succeed(
  Database,
  {
    // Simulate a database query
    query: (sql: string) => Effect.log(`Executing query: ${sql}`).pipe(Effect.as([]))
  }
)

//      ┌─── Effect<unknown[], never, Database>
//      ▼
const program = Effect.gen(function*() {
  const database = yield* Database
  const result = yield* database.query("SELECT * FROM users")
  return result
})

//      ┌─── Effect<unknown[], never, never>
//      ▼
const runnable = Effect.provide(program, DatabaseLive)

// Effect.runPromise(runnable).then(console.log)
// Output:
// timestamp=... level=INFO fiber=#0 message="Executing query: SELECT * FROM users"
// []
@since ― 2.0.0
provide(
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive),
47
    
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const catchAllCause: <never, void, never, never>(f: (cause: Cause<never>) => Effect.Effect<void, never, never>) => <A, R>(self: Effect.Effect<A, never, R>) => Effect.Effect<void | A, never, R> (+1 overload)
Handles both recoverable and unrecoverable errors by providing a recovery
effect.
When to Use
The catchAllCause function allows you to handle all errors, including
unrecoverable defects, by providing a recovery effect. The recovery logic is
based on the Cause of the error, which provides detailed information about
the failure.
When to Recover from Defects
Defects are unexpected errors that typically shouldn't be recovered from, as
they often indicate serious issues. However, in some cases, such as
dynamically loaded plugins, controlled recovery might be needed.
@example 
// Title: Recovering from All Errors
import { Cause, Effect } from "effect"

// Define an effect that may fail with a recoverable or unrecoverable error
const program = Effect.fail("Something went wrong!")

// Recover from all errors by examining the cause
const recovered = program.pipe(
  Effect.catchAllCause((cause) =>
    Cause.isFailType(cause)
      ? Effect.succeed("Recovered from a regular error")
      : Effect.succeed("Recovered from a defect")
  )
)

// Effect.runPromise(recovered).then(console.log)
// Output: "Recovered from a regular error"
@since ― 2.0.0
catchAllCause(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const logError: (...message: ReadonlyArray<any>) => Effect.Effect<void, never, never>
Logs messages at the ERROR log level.
Details
This function logs messages at the ERROR level, suitable for reporting
application errors or failures. These logs are typically used for unexpected
issues that need immediate attention.
@since ― 2.0.0
logError)
48
  )
49
)
50
/*
51
Output:
52
timestamp=... level=INFO fiber=#0 message=client
53
timestamp=... level=INFO fiber=#0 message=/api
54
timestamp=... level=INFO fiber=#0 message=/authN
55
timestamp=... level=INFO fiber=#0 message=/authZ
56
timestamp=... level=INFO fiber=#0 message="/payment Gateway"
57
timestamp=... level=INFO fiber=#0 message=DB
58
timestamp=... level=INFO fiber=#0 message="Ext. Merchant"
59
timestamp=... level=INFO fiber=#0 message=/dispatch
60
timestamp=... level=INFO fiber=#0 message=/dispatch/search
61
timestamp=... level=INFO fiber=#3 message=/poll
62
timestamp=... level=INFO fiber=#4 message=/poll
63
timestamp=... level=INFO fiber=#5 message=/poll
64
timestamp=... level=INFO fiber=#0 message=/pollDriver/{id}
65
*/

Visualize Traces. Now, open your web browser and go to http://localhost:3000/explore. You will see a generated Trace ID on the web page. Click on it to see the details of the trace.

Integrations

Sentry

To send span data directly to Sentry for analysis, replace the default span processor with Sentry’s implementation. This allows you to use Sentry as a backend for tracing and debugging.

Example (Configuring Sentry for Tracing)

1
import { 
import NodeSdk
NodeSdk } from "@effect/opentelemetry"
2
import { 
class SentrySpanProcessor
Converts OpenTelemetry Spans to Sentry Spans and sends them to Sentry via
the Sentry SDK.
SentrySpanProcessor } from "@sentry/opentelemetry"
3

4
const 
const NodeSdkLive: Layer<Resource, never, never>
NodeSdkLive = 
import NodeSdk
NodeSdk.
const layer: (evaluate: LazyArg<NodeSdk.Configuration>) => Layer<Resource> (+1 overload)@since ― 1.0.0
layer(() => ({
5
  
Configuration.resource?: {
    readonly serviceName: string;
    readonly serviceVersion?: string;
    readonly attributes?: ResourceAttributes;
} | undefined
resource: { 
serviceName: string
serviceName: "example" },
6
  
Configuration.spanProcessor?: SpanProcessor | readonly SpanProcessor[] | undefined
spanProcessor: new 
new SentrySpanProcessor(options?: {
    timeout?: number;
}): SentrySpanProcessor
Converts OpenTelemetry Spans to Sentry Spans and sends them to Sentry via
the Sentry SDK.
SentrySpanProcessor()
7
}))