<E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(
self: Effect<A, E, R>
) => Effect<A, E | E2, R2 | R>
<A, E, R, X, E2, R2>(
self: Effect<A, E, R>,
f: (e: E) => Effect<X, E2, R2>
): Effect<A, E | E2, R | R2>Runs an effectful operation when the source effect fails, while preserving the original failure when the operation succeeds.
Details
Use this for logging, metrics, or other failure-side observations. If the
operation passed to tapError fails, that error is also represented in the
returned effect's error channel.
Example (Running effects on failure)
import { Console, Effect } from "effect"
// Simulate a task that fails with an error
const task: Effect.Effect<number, string> = Effect.fail("NetworkError")
// Use tapError to log the error message when the task fails
const tapping = Effect.tapError(
task,
(error) => Console.log(`expected error: ${error}`)
)
Effect.runFork(tapping)
// Output:
// expected error: NetworkErrorexport const const tapError: {
<E, X, E2, R2>(
f: (e: NoInfer<E>) => Effect<X, E2, R2>
): <A, R>(
self: Effect<A, E, R>
) => Effect<A, E | E2, R2 | R>
<A, E, R, X, E2, R2>(
self: Effect<A, E, R>,
f: (e: E) => Effect<X, E2, R2>
): Effect<A, E | E2, R | R2>
}
Runs an effectful operation when the source effect fails, while preserving
the original failure when the operation succeeds.
Details
Use this for logging, metrics, or other failure-side observations. If the
operation passed to tapError fails, that error is also represented in the
returned effect's error channel.
Example (Running effects on failure)
import { Console, Effect } from "effect"
// Simulate a task that fails with an error
const task: Effect.Effect<number, string> = Effect.fail("NetworkError")
// Use tapError to log the error message when the task fails
const tapping = Effect.tapError(
task,
(error) => Console.log(`expected error: ${error}`)
)
Effect.runFork(tapping)
// Output:
// expected error: NetworkError
tapError: {
<function (type parameter) E in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>E, function (type parameter) X in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>X, function (type parameter) E2 in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>E2, function (type parameter) R2 in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>R2>(
f: (e: NoInfer<E>) => Effect<X, E2, R2>f: (e: NoInfer<E>e: type NoInfer<A> = [A][A extends any ? 0 : never]Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) E in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>E>) => interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) X in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>X, function (type parameter) E2 in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>E2, function (type parameter) R2 in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>R2>
): <function (type parameter) A in <A, R>(self: Effect<A, E, R>): Effect<A, E | E2, R2 | R>A, function (type parameter) R in <A, R>(self: Effect<A, E, R>): Effect<A, E | E2, R2 | R>R>(self: Effect<A, E, R>(parameter) self: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A in <A, R>(self: Effect<A, E, R>): Effect<A, E | E2, R2 | R>A, function (type parameter) E in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>E, function (type parameter) R in <A, R>(self: Effect<A, E, R>): Effect<A, E | E2, R2 | R>R>) => interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A in <A, R>(self: Effect<A, E, R>): Effect<A, E | E2, R2 | R>A, function (type parameter) E in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>E | function (type parameter) E2 in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>E2, function (type parameter) R2 in <E, X, E2, R2>(f: (e: NoInfer<E>) => Effect<X, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A, E | E2, R2 | R>R2 | function (type parameter) R in <A, R>(self: Effect<A, E, R>): Effect<A, E | E2, R2 | R>R>
<function (type parameter) A in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>R, function (type parameter) X in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>X, function (type parameter) E2 in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>R2>(
self: Effect<A, E, R>(parameter) self: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>R>,
f: (e: E) => Effect<X, E2, R2>f: (e: Ee: function (type parameter) E in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>E) => interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) X in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>X, function (type parameter) E2 in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>R2>
): interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, X, E2, R2>(self: Effect<A, E, R>, f: (e: E) => Effect<X, E2, R2>): Effect<A, E | E2, R | R2>R2>
} = import internalinternal.const tapError: {
<E, B, E2, R2>(
f: (e: NoInfer<E>) => Effect.Effect<B, E2, R2>
): <A, R>(
self: Effect.Effect<A, E, R>
) => Effect.Effect<A, E | E2, R | R2>
<A, E, R, B, E2, R2>(
self: Effect.Effect<A, E, R>,
f: (e: NoInfer<E>) => Effect.Effect<B, E2, R2>
): Effect.Effect<A, E | E2, R | R2>
}