<A, E>(queue: Queue.Dequeue<A, E>): Channel<A, Exclude<E, Cause.Done>>Creates a channel from a queue.
Example (Creating channels from queues)
import { Channel, Data, Effect, Queue } from "effect"
class QueueError extends Data.TaggedError("QueueError")<{
readonly reason: string
}> {}
const program = Effect.gen(function*() {
// Create a bounded queue
const queue = yield* Queue.bounded<string, QueueError>(10)
// Add some items to the queue
yield* Queue.offer(queue, "item1")
yield* Queue.offer(queue, "item2")
yield* Queue.offer(queue, "item3")
// Create a channel from the queue
const channel = Channel.fromQueue(queue)
// The channel will read items from the queue one by one
return channel
})
// Sliding queue example
const slidingProgram = Effect.gen(function*() {
const slidingQueue = yield* Queue.sliding<number, QueueError>(5)
yield* Queue.offerAll(slidingQueue, [1, 2, 3, 4, 5, 6])
return Channel.fromQueue(slidingQueue)
})export const const fromQueue: <A, E>(
queue: Queue.Dequeue<A, E>
) => Channel<A, Exclude<E, Cause.Done>>
Creates a channel from a queue.
Example (Creating channels from queues)
import { Channel, Data, Effect, Queue } from "effect"
class QueueError extends Data.TaggedError("QueueError")<{
readonly reason: string
}> {}
const program = Effect.gen(function*() {
// Create a bounded queue
const queue = yield* Queue.bounded<string, QueueError>(10)
// Add some items to the queue
yield* Queue.offer(queue, "item1")
yield* Queue.offer(queue, "item2")
yield* Queue.offer(queue, "item3")
// Create a channel from the queue
const channel = Channel.fromQueue(queue)
// The channel will read items from the queue one by one
return channel
})
// Sliding queue example
const slidingProgram = Effect.gen(function*() {
const slidingQueue = yield* Queue.sliding<number, QueueError>(5)
yield* Queue.offerAll(slidingQueue, [1, 2, 3, 4, 5, 6])
return Channel.fromQueue(slidingQueue)
})
fromQueue = <function (type parameter) A in <A, E>(queue: Queue.Dequeue<A, E>): Channel<A, Exclude<E, Cause.Done>>A, function (type parameter) E in <A, E>(queue: Queue.Dequeue<A, E>): Channel<A, Exclude<E, Cause.Done>>E>(
queue: Queue.Dequeue<A, E>(parameter) queue: {
strategy: "suspend" | "dropping" | "sliding";
dispatcher: SchedulerDispatcher;
capacity: number;
messages: MutableList.MutableList<any>;
state: Queue.State<any, any>;
scheduleRunning: boolean;
toString: () => string;
toJSON: () => unknown;
}
import QueueQueue.interface Dequeue<out A, out E = never>A Dequeue is a queue that can be taken from.
Details
This interface represents the read-only part of a Queue, allowing you to take
elements from the queue but not offer elements to it.
Example (Taking through dequeue handles)
import { Effect, Queue } from "effect"
const program = Effect.gen(function*() {
const queue = yield* Queue.bounded<string, never>(10)
// A Dequeue can only take elements
const dequeue: Queue.Dequeue<string> = queue
// Pre-populate the queue
yield* Queue.offerAll(queue, ["a", "b", "c"])
// Take elements using dequeue interface
const item = yield* Queue.take(dequeue)
console.log(item) // "a"
})
Companion namespace containing type-level metadata for the Dequeue
read-only queue interface.
Dequeue<function (type parameter) A in <A, E>(queue: Queue.Dequeue<A, E>): Channel<A, Exclude<E, Cause.Done>>A, function (type parameter) E in <A, E>(queue: Queue.Dequeue<A, E>): Channel<A, Exclude<E, Cause.Done>>E>
): 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) A in <A, E>(queue: Queue.Dequeue<A, E>): Channel<A, Exclude<E, Cause.Done>>A, type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) E in <A, E>(queue: Queue.Dequeue<A, E>): Channel<A, Exclude<E, Cause.Done>>E, import CauseCause.type Cause.Done = /*unresolved*/ anyDone>> => 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 QueueQueue.const take: <A, E>(
self: Dequeue<A, E>
) => Effect<A, E>
Takes a single message from the queue, or wait for a message to be
available.
Details
If the queue is done, it will fail with Done. If the
queue fails, the Effect will fail with the error.
Example (Taking one value)
import { Cause, Effect, Queue } from "effect"
const program = Effect.gen(function*() {
const queue = yield* Queue.bounded<string, Cause.Done>(3)
// Add some messages
yield* Queue.offer(queue, "first")
yield* Queue.offer(queue, "second")
// Take messages one by one
const msg1 = yield* Queue.take(queue)
const msg2 = yield* Queue.take(queue)
console.log(msg1, msg2) // "first", "second"
// End the queue
yield* Queue.end(queue)
// Taking from an ended queue fails with Done
const result = yield* Effect.match(Queue.take(queue), {
onFailure: (error: Cause.Done) => true,
onSuccess: (value: string) => false
})
console.log("Queue ended:", result) // true
})
take(queue: Queue.Dequeue<A, E>(parameter) queue: {
strategy: "suspend" | "dropping" | "sliding";
dispatcher: SchedulerDispatcher;
capacity: number;
messages: MutableList.MutableList<any>;
state: Queue.State<any, any>;
scheduleRunning: boolean;
toString: () => string;
toJSON: () => unknown;
}