<OutElem, A, E, R>(
onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>
): <OutErr, OutDone, InElem, InErr, InDone, Env>(
self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>
) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>
<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(
self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>,
onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>
): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Runs an effect the first time the channel emits an output element.
When to use
Use when initialization depends on the first output element rather than only on channel startup.
Details
The effect receives the first emitted element. The first element is still emitted unchanged. The effect is not run if the channel completes without emitting an element.
hooks
Source effect/Channel.ts:705023 lines
export const const onFirst: {
<OutElem, A, E, R>(
onFirst: (
element: Types.NoInfer<OutElem>
) => Effect.Effect<A, E, R>
): <
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
OutElem,
OutErr | E,
OutDone,
InElem,
InErr,
InDone,
Env | R
>
<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
A,
E,
R
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
onFirst: (
element: Types.NoInfer<OutElem>
) => Effect.Effect<A, E, R>
): Channel<
OutElem,
OutErr | E,
OutDone,
InElem,
InErr,
InDone,
Env | R
>
}
Runs an effect the first time the channel emits an output element.
When to use
Use when initialization depends on the first output element rather than only
on channel startup.
Details
The effect receives the first emitted element. The first element is still
emitted unchanged. The effect is not run if the channel completes without
emitting an element.
onFirst: {
<function (type parameter) OutElem in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem, function (type parameter) A in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>A, function (type parameter) E in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>E, function (type parameter) R in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>R>(
onFirst: (
element: Types.NoInfer<OutElem>
) => Effect.Effect<A, E, R>
element: Types.NoInfer<OutElem>element: import TypesTypes.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) OutElem in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem>) => import EffectEffect.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 <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>A, function (type parameter) E in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>E, function (type parameter) R in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>R>
): <function (type parameter) OutErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutErr, function (type parameter) OutDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutDone, function (type parameter) InElem in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InElem, function (type parameter) InErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InErr, function (type parameter) InDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InDone, function (type parameter) Env in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Env>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(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; <…;
}
interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem, function (type parameter) OutErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutErr, function (type parameter) OutDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutDone, function (type parameter) InElem in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InElem, function (type parameter) InErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InErr, function (type parameter) InDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InDone, function (type parameter) Env in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Env>
) => interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem, function (type parameter) OutErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutErr | function (type parameter) E in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>E, function (type parameter) OutDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutDone, function (type parameter) InElem in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InElem, function (type parameter) InErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InErr, function (type parameter) InDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InDone, function (type parameter) Env in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Env | function (type parameter) R in <OutElem, A, E, R>(onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>R>
<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Env, function (type parameter) A in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>A, function (type parameter) E in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>E, function (type parameter) R in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>R>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(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; <…;
}
interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Env>,
onFirst: (
element: Types.NoInfer<OutElem>
) => Effect.Effect<A, E, R>
element: Types.NoInfer<OutElem>element: import TypesTypes.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) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem>) => import EffectEffect.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 <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>A, function (type parameter) E in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>E, function (type parameter) R in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>R>
): interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutErr | function (type parameter) E in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>E, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Env | function (type parameter) R in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>R>
} = dual<(...args: Array<any>) => any, <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>>(arity: 2, body: <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>): ((...args: Array<any>) => any) & (<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>) => Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>) (+1 overload)Creates a function that can be called in data-first style or data-last
(pipe-friendly) style.
When to use
Use to expose one implementation through both direct and pipe-friendly
call styles.
Details
Pass either the arity of the uncurried function or a predicate that decides
whether the current call is data-first. Arity is the common case. Use a
predicate when optional arguments make arity ambiguous.
Example (Selecting data-first or data-last style by arity)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(2, (self, that) => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Defining overloads with call signatures)
import { Function, pipe } from "effect"
const sum: {
(that: number): (self: number) => number
(self: number, that: number): number
} = Function.dual(2, (self: number, that: number): number => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Selecting data-first or data-last style with a predicate)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(
(args) => args.length === 2,
(self, that) => self + that
)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
dual(2, <function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Env, function (type parameter) A in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>A, function (type parameter) E in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>E, function (type parameter) R in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>R>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(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; <…;
}
interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Env>,
onFirst: (
element: Types.NoInfer<OutElem>
) => Effect.Effect<A, E, R>
element: Types.NoInfer<OutElem>element: import TypesTypes.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) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem>) => import EffectEffect.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 <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>A, function (type parameter) E in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>E, function (type parameter) R in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>R>
): interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutErr | function (type parameter) E in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>E, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>Env | function (type parameter) R in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, A, E, R>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, onFirst: (element: Types.NoInfer<OutElem>) => Effect.Effect<A, E, R>): Channel<OutElem, OutErr | E, OutDone, InElem, InErr, InDone, Env | R>R> =>
const transformPull: <
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
OutElem2,
OutErr2,
OutDone2,
Env2,
OutErrX,
EnvX
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
f: (
pull: Pull.Pull<OutElem, OutErr, OutDone>,
scope: Scope.Scope
) => Effect.Effect<
Pull.Pull<OutElem2, OutErr2, OutDone2, Env2>,
OutErrX,
EnvX
>
) => Channel<
OutElem2,
Pull.ExcludeDone<OutErr2> | OutErrX,
OutDone2,
InElem,
InErr,
InDone,
Env | Env2 | EnvX
>
Transforms a Channel by applying a function to its Pull implementation.
Example (Transforming pull behavior)
import { Channel, Effect } from "effect"
// Transform a channel by modifying its pull behavior
const originalChannel = Channel.fromIterable([1, 2, 3])
const transformedChannel = Channel.transformPull(
originalChannel,
(pull, scope) =>
Effect.succeed(
Effect.map(pull, (value) => value * 2)
)
)
// Outputs: 2, 4, 6
transformPull(self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(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; <…;
}
pull: Pull.Pull<
OutElem,
OutErr,
OutDone,
never
>
(parameter) pull: {
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;
}
import EffectEffect.const sync: <A>(
thunk: LazyArg<A>
) => Effect<A>
Creates an Effect that represents a synchronous side-effectful computation.
When to use
Use when you need to wrap a synchronous side-effectful operation that is not
expected to throw.
Details
The provided function is evaluated lazily when the effect runs.
Gotchas
The function must not throw. If it throws, the thrown value is treated as a
defect, not as a typed failure. Use try when throwing is expected.
Example (Capturing synchronous logging in an Effect)
import { Effect } from "effect"
const log = (message: string) =>
Effect.sync(() => {
console.log(message) // side effect
})
// ┌─── Effect<void, never, never>
// ▼
const program = log("Hello, World!")
sync(() => {
let let isFirst: booleanisFirst = true
const const pullFirst: Effect.Effect<
OutElem,
OutErr | E | Cause.Done<OutDone>,
R
>
const pullFirst: {
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;
}
import EffectEffect.const tap: {
<A, B, E2, R2>(
f: (a: NoInfer<A>) => Effect<B, E2, R2>
): <E, R>(
self: Effect<A, E, R>
) => Effect<A, E | E2, R | R2>
<B, E2, R2>(f: Effect<B, E2, R2>): <A, E, R>(
self: Effect<A, E, R>
) => Effect<A, E | E2, R | R2>
<A, E, R, B, E2, R2>(
self: Effect<A, E, R>,
f: (a: NoInfer<A>) => Effect<B, E2, R2>
): Effect<A, E | E2, R | R2>
<A, E, R, B, E2, R2>(
self: Effect<A, E, R>,
f: Effect<B, E2, R2>
): Effect<A, E | E2, R | R2>
}
pull: Pull.Pull<
OutElem,
OutErr,
OutDone,
never
>
(parameter) pull: {
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;
}
element: Types.NoInfer<OutElem>element) => {
let isFirst: booleanisFirst = false
return onFirst: (
element: Types.NoInfer<OutElem>
) => Effect.Effect<A, E, R>
element: Types.NoInfer<OutElem>element)
})
return import EffectEffect.const suspend: <A, E, R>(
effect: LazyArg<Effect<A, E, R>>
) => Effect<A, E, R>
Creates an Effect lazily, delaying construction until it is needed.
When to use
Use when you need to defer the evaluation of an effect until it is required.
Details
suspend takes a thunk that represents an effect and delays creating it
until the suspended effect is evaluated. This is useful for optimizing
expensive computations, managing circular dependencies such as recursive
functions, and helping TypeScript unify return types when branches construct
different effects. Any side effects or scoped captures inside the thunk are
re-executed on each invocation.
Example (Lazily evaluating side effects)
import { Effect } from "effect"
let i = 0
const bad = Effect.succeed(i++)
const good = Effect.suspend(() => Effect.succeed(i++))
console.log(Effect.runSync(bad)) // Output: 0
console.log(Effect.runSync(bad)) // Output: 0
console.log(Effect.runSync(good)) // Output: 1
console.log(Effect.runSync(good)) // Output: 2
Example (Suspending recursive Fibonacci evaluation)
import { Effect } from "effect"
const blowsUp = (n: number): Effect.Effect<number> =>
n < 2
? Effect.succeed(1)
: Effect.zipWith(blowsUp(n - 1), blowsUp(n - 2), (a, b) => a + b)
// console.log(Effect.runSync(blowsUp(32)))
// crash: JavaScript heap out of memory
const allGood = (n: number): Effect.Effect<number> =>
n < 2
? Effect.succeed(1)
: Effect.zipWith(
Effect.suspend(() => allGood(n - 1)),
Effect.suspend(() => allGood(n - 2)),
(a, b) => a + b
)
console.log(Effect.runSync(allGood(32)))
// Output: 3524578
Example (Helping TypeScript infer recursive effect types)
import { Effect } from "effect"
// Without suspend, TypeScript may struggle with type inference.
// Inferred type:
// (a: number, b: number) =>
// Effect<never, Error, never> | Effect<number, never, never>
const withoutSuspend = (a: number, b: number) =>
b === 0
? Effect.fail(new Error("Cannot divide by zero"))
: Effect.succeed(a / b)
// Using suspend to unify return types.
// Inferred type:
// (a: number, b: number) => Effect<number, Error, never>
const withSuspend = (a: number, b: number) =>
Effect.suspend(() =>
b === 0
? Effect.fail(new Error("Cannot divide by zero"))
: Effect.succeed(a / b)
)
suspend(() => let isFirst: booleanisFirst ? const pullFirst: Effect.Effect<
OutElem,
OutErr | E | Cause.Done<OutDone>,
R
>
const pullFirst: {
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;
}
pull: Pull.Pull<
OutElem,
OutErr,
OutDone,
never
>
(parameter) pull: {
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;
}
Referenced by 2 symbols