<A, E, R>(effect: Effect.Effect<A, E, R>): Channel<
never,
Pull.ExcludeDone<E>,
A,
unknown,
unknown,
unknown,
R
>Creates a channel that evaluates an effect and uses its successful value as the channel's done value without emitting any output elements.
Details
If the effect fails, the channel fails with the effect's error.
export const const fromEffectDone: <A, E, R>(
effect: Effect.Effect<A, E, R>
) => Channel<
never,
Pull.ExcludeDone<E>,
A,
unknown,
unknown,
unknown,
R
>
Creates a channel that evaluates an effect and uses its successful value as
the channel's done value without emitting any output elements.
Details
If the effect fails, the channel fails with the effect's error.
fromEffectDone = <function (type parameter) A in <A, E, R>(effect: Effect.Effect<A, E, R>): Channel<never, Pull.ExcludeDone<E>, A, unknown, unknown, unknown, R>A, function (type parameter) E in <A, E, R>(effect: Effect.Effect<A, E, R>): Channel<never, Pull.ExcludeDone<E>, A, unknown, unknown, unknown, R>E, function (type parameter) R in <A, E, R>(effect: Effect.Effect<A, E, R>): Channel<never, Pull.ExcludeDone<E>, A, unknown, unknown, unknown, R>R>(
effect: Effect.Effect<A, E, R>(parameter) effect: {
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.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>(effect: Effect.Effect<A, E, R>): Channel<never, Pull.ExcludeDone<E>, A, unknown, unknown, unknown, R>A, function (type parameter) E in <A, E, R>(effect: Effect.Effect<A, E, R>): Channel<never, Pull.ExcludeDone<E>, A, unknown, unknown, unknown, R>E, function (type parameter) R in <A, E, R>(effect: Effect.Effect<A, E, R>): Channel<never, Pull.ExcludeDone<E>, A, unknown, unknown, unknown, 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<never, import PullPull.type ExcludeDone<E> =
E extends Cause.Done<any> ? never : E
Excludes Cause.Done completion signals from an error type union.
When to use
Use to describe the ordinary error type that remains after Cause.Done
completion signals have been handled or filtered out of an error union.
ExcludeDone<function (type parameter) E in <A, E, R>(effect: Effect.Effect<A, E, R>): Channel<never, Pull.ExcludeDone<E>, A, unknown, unknown, unknown, R>E>, function (type parameter) A in <A, E, R>(effect: Effect.Effect<A, E, R>): Channel<never, Pull.ExcludeDone<E>, A, unknown, unknown, unknown, R>A, unknown, unknown, unknown, function (type parameter) R in <A, E, R>(effect: Effect.Effect<A, E, R>): Channel<never, Pull.ExcludeDone<E>, A, unknown, unknown, unknown, R>R> =>
const fromPull: <
OutElem,
OutErr,
OutDone,
EX,
EnvX,
Env
>(
effect: Effect.Effect<
Pull.Pull<OutElem, OutErr, OutDone, EnvX>,
EX,
Env
>
) => Channel<
OutElem,
Pull.ExcludeDone<OutErr> | EX,
OutDone,
unknown,
unknown,
unknown,
Env | EnvX
>
Creates a Channel from an Effect that produces a Pull.
Example (Creating channels from pulls)
import { Channel, Effect } from "effect"
const channel = Channel.fromPull(
Effect.succeed(Effect.succeed(42))
)
fromPull(import EffectEffect.const succeed: <A>(value: A) => Effect<A>Creates an Effect that always succeeds with a given value.
When to use
Use when an effect should complete successfully with a specific value without any errors
or external dependencies.
Example (Creating a successful effect)
import { Effect } from "effect"
// Creating an effect that represents a successful scenario
//
// ┌─── Effect<number, never, never>
// ▼
const success = Effect.succeed(42)
succeed(import EffectEffect.const flatMap: {
<A, B, E1, R1>(
f: (a: A) => Effect<B, E1, R1>
): <E, R>(
self: Effect<A, E, R>
) => Effect<B, E1 | E, R1 | R>
<A, E, R, B, E1, R1>(
self: Effect<A, E, R>,
f: (a: A) => Effect<B, E1, R1>
): Effect<B, E | E1, R | R1>
}
effect: Effect.Effect<A, E, R>(parameter) effect: {
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 CauseCause.done)))