<E, E2>(f: (e: E) => E2): <A, R>(
self: Effect<A, E, R>
) => Effect<A, E2, R>
<A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>Transforms the failure value of an effect without changing its success value.
When to use
Use to translate an Effect's typed failures while leaving successful values
unchanged.
Details
Only the failure channel is transformed. The success channel and requirements are preserved.
Example (Transforming the error channel)
import { Data, Effect } from "effect"
class TaskError extends Data.TaggedError("TaskError")<{ readonly message: string }> {}
// ┌─── Effect<number, string, never>
// ▼
const simulatedTask = Effect.fail("Oh no!").pipe(Effect.as(1))
// ┌─── Effect<number, TaskError, never>
// ▼
const mapped = Effect.mapError(
simulatedTask,
(message) => new TaskError({ message })
)export const const mapError: {
<E, E2>(f: (e: E) => E2): <A, R>(
self: Effect<A, E, R>
) => Effect<A, E2, R>
<A, E, R, E2>(
self: Effect<A, E, R>,
f: (e: E) => E2
): Effect<A, E2, R>
}
Transforms the failure value of an effect without changing its success value.
When to use
Use to translate an Effect's typed failures while leaving successful values
unchanged.
Details
Only the failure channel is transformed. The success channel and requirements
are preserved.
Example (Transforming the error channel)
import { Data, Effect } from "effect"
class TaskError extends Data.TaggedError("TaskError")<{ readonly message: string }> {}
// ┌─── Effect<number, string, never>
// ▼
const simulatedTask = Effect.fail("Oh no!").pipe(Effect.as(1))
// ┌─── Effect<number, TaskError, never>
// ▼
const mapped = Effect.mapError(
simulatedTask,
(message) => new TaskError({ message })
)
mapError: {
<function (type parameter) E in <E, E2>(f: (e: E) => E2): <A, R>(self: Effect<A, E, R>) => Effect<A, E2, R>E, function (type parameter) E2 in <E, E2>(f: (e: E) => E2): <A, R>(self: Effect<A, E, R>) => Effect<A, E2, R>E2>(f: (e: E) => E2f: (e: Ee: function (type parameter) E in <E, E2>(f: (e: E) => E2): <A, R>(self: Effect<A, E, R>) => Effect<A, E2, R>E) => function (type parameter) E2 in <E, E2>(f: (e: E) => E2): <A, R>(self: Effect<A, E, R>) => Effect<A, E2, R>E2): <function (type parameter) A in <A, R>(self: Effect<A, E, R>): Effect<A, E2, R>A, function (type parameter) R in <A, R>(self: Effect<A, E, R>): Effect<A, E2, 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, E2, R>A, function (type parameter) E in <E, E2>(f: (e: E) => E2): <A, R>(self: Effect<A, E, R>) => Effect<A, E2, R>E, function (type parameter) R in <A, R>(self: Effect<A, E, R>): Effect<A, E2, 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, E2, R>A, function (type parameter) E2 in <E, E2>(f: (e: E) => E2): <A, R>(self: Effect<A, E, R>) => Effect<A, E2, R>E2, function (type parameter) R in <A, R>(self: Effect<A, E, R>): Effect<A, E2, R>R>
<function (type parameter) A in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>A, function (type parameter) E in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>E, function (type parameter) R in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>R, function (type parameter) E2 in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>E2>(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, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>A, function (type parameter) E in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>E, function (type parameter) R in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>R>, f: (e: E) => E2f: (e: Ee: function (type parameter) E in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>E) => function (type parameter) E2 in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>E2): 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, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>A, function (type parameter) E2 in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>E2, function (type parameter) R in <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>R>
} = import internalinternal.const mapError: {
<E, E2>(f: (e: E) => E2): <A, R>(
self: Effect.Effect<A, E, R>
) => Effect.Effect<A, E2, R>
<A, E, R, E2>(
self: Effect.Effect<A, E, R>,
f: (e: E) => E2
): Effect.Effect<A, E2, R>
}