<A>(pubsub: PubSub.PubSub<A>): Channel<A>Creates a channel from a PubSub that outputs individual values.
Details
This constructor creates a channel that reads from a PubSub by automatically subscribing to it. The channel outputs individual values as they are published to the PubSub, making it ideal for real-time streaming scenarios.
Example (Creating channels from PubSubs)
import { Channel, Data, Effect, PubSub } from "effect"
class StreamError extends Data.TaggedError("StreamError")<{
readonly message: string
}> {}
const program = Effect.gen(function*() {
const pubsub = yield* PubSub.bounded<number>(16)
// Create a channel that reads individual values
const channel = Channel.fromPubSub(pubsub)
// Publish some values
yield* PubSub.publish(pubsub, 1)
yield* PubSub.publish(pubsub, 2)
yield* PubSub.publish(pubsub, 3)
// The channel will output: 1, 2, 3 (individual values)
return channel
})Example (Streaming PubSub notifications)
import { Channel, Effect, PubSub } from "effect"
const notificationService = Effect.gen(function*() {
const notificationPubSub = yield* PubSub.bounded<string>(50)
// Create a channel for real-time notifications
const notificationChannel = Channel.fromPubSub(notificationPubSub)
// Transform notifications to add timestamps
const receivedAt = "2024-01-01T00:00:00.000Z"
const timestampedChannel = Channel.map(notificationChannel, (message) => ({
message,
receivedAt,
id: `notification:${message}`
}))
return timestampedChannel
})Example (Processing PubSub events)
import { Channel, Effect, PubSub } from "effect"
interface DomainEvent {
readonly type: string
readonly payload: unknown
readonly timestamp: number
}
const eventProcessor = Effect.gen(function*() {
const eventPubSub = yield* PubSub.bounded<DomainEvent>(100)
// Create a channel for processing domain events
const eventChannel = Channel.fromPubSub(eventPubSub)
// Filter and transform events
const processedChannel = Channel.map(eventChannel, (event) => {
if (event.type === "user.created") {
return {
...event,
processed: true,
processedAt: event.timestamp + 1
}
}
return event
})
return processedChannel
})constructors
Source effect/Channel.ts:15193 lines
export const const fromPubSub: <A>(
pubsub: PubSub.PubSub<A>
) => Channel<A>
Creates a channel from a PubSub that outputs individual values.
Details
This constructor creates a channel that reads from a PubSub by automatically
subscribing to it. The channel outputs individual values as they are published
to the PubSub, making it ideal for real-time streaming scenarios.
Example (Creating channels from PubSubs)
import { Channel, Data, Effect, PubSub } from "effect"
class StreamError extends Data.TaggedError("StreamError")<{
readonly message: string
}> {}
const program = Effect.gen(function*() {
const pubsub = yield* PubSub.bounded<number>(16)
// Create a channel that reads individual values
const channel = Channel.fromPubSub(pubsub)
// Publish some values
yield* PubSub.publish(pubsub, 1)
yield* PubSub.publish(pubsub, 2)
yield* PubSub.publish(pubsub, 3)
// The channel will output: 1, 2, 3 (individual values)
return channel
})
Example (Streaming PubSub notifications)
import { Channel, Effect, PubSub } from "effect"
const notificationService = Effect.gen(function*() {
const notificationPubSub = yield* PubSub.bounded<string>(50)
// Create a channel for real-time notifications
const notificationChannel = Channel.fromPubSub(notificationPubSub)
// Transform notifications to add timestamps
const receivedAt = "2024-01-01T00:00:00.000Z"
const timestampedChannel = Channel.map(notificationChannel, (message) => ({
message,
receivedAt,
id: `notification:${message}`
}))
return timestampedChannel
})
Example (Processing PubSub events)
import { Channel, Effect, PubSub } from "effect"
interface DomainEvent {
readonly type: string
readonly payload: unknown
readonly timestamp: number
}
const eventProcessor = Effect.gen(function*() {
const eventPubSub = yield* PubSub.bounded<DomainEvent>(100)
// Create a channel for processing domain events
const eventChannel = Channel.fromPubSub(eventPubSub)
// Filter and transform events
const processedChannel = Channel.map(eventChannel, (event) => {
if (event.type === "user.created") {
return {
...event,
processed: true,
processedAt: event.timestamp + 1
}
}
return event
})
return processedChannel
})
fromPubSub = <function (type parameter) A in <A>(pubsub: PubSub.PubSub<A>): Channel<A>A>(
pubsub: PubSub.PubSub<A>(parameter) pubsub: {
pubsub: PubSub.Atomic<A>;
subscribers: PubSub.Subscribers<A>;
scope: Scope.Closeable;
shutdownHook: Latch.Latch;
shutdownFlag: MutableRef.MutableRef<boolean>;
strategy: PubSub.Strategy<A>;
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; <…;
}
import PubSubPubSub.interface PubSub<in out A>A PubSub<A> is an asynchronous message hub into which publishers can publish
messages of type A and subscribers can subscribe to take messages of type
A.
Example (Publishing and subscribing to messages)
import { Effect, PubSub } from "effect"
const program = Effect.gen(function*() {
// Create a bounded PubSub with capacity 10
const pubsub = yield* PubSub.bounded<string>(10)
// Subscribe and consume messages
yield* Effect.scoped(Effect.gen(function*() {
const subscription = yield* PubSub.subscribe(pubsub)
// Publish messages
yield* PubSub.publish(pubsub, "Hello")
yield* PubSub.publish(pubsub, "World")
const message1 = yield* PubSub.take(subscription)
const message2 = yield* PubSub.take(subscription)
console.log(message1, message2) // "Hello", "World"
}))
})
Companion namespace containing the low-level building blocks used by
PubSub, including atomic implementations, backing subscriptions, replay
windows, and delivery strategies.
PubSub<function (type parameter) A in <A>(pubsub: PubSub.PubSub<A>): Channel<A>A>
): 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>(pubsub: PubSub.PubSub<A>): Channel<A>A> => const unwrap: <
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
R2,
E,
R
>(
channel: Effect.Effect<
Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
R2
>,
E,
R
>
) => Channel<
OutElem,
E | OutErr,
OutDone,
InElem,
InErr,
InDone,
Exclude<R, Scope.Scope> | R2
>
Constructs a Channel from a scoped effect that will result in a
Channel if successful.
Example (Unwrapping channel effects)
import { Channel, Data, Effect } from "effect"
class UnwrapError extends Data.TaggedError("UnwrapError")<{
readonly reason: string
}> {}
// Create an effect that produces a channel
const channelEffect = Effect.succeed(
Channel.fromIterable([1, 2, 3])
)
// Unwrap the effect to get the channel
const unwrappedChannel = Channel.unwrap(channelEffect)
// The resulting channel outputs: 1, 2, 3
unwrap(import EffectEffect.const map: {
<A, B>(f: (a: A) => B): <E, R>(
self: Effect<A, E, R>
) => Effect<B, E, R>
<A, E, R, B>(
self: Effect<A, E, R>,
f: (a: A) => B
): Effect<B, E, R>
}
import PubSubPubSub.const subscribe: <A>(
self: PubSub<A>
) => Effect.Effect<
Subscription<A>,
never,
Scope.Scope
>
Subscribes to receive messages from the PubSub. The resulting subscription can
be evaluated multiple times within the scope to take a message from the PubSub
each time.
Example (Subscribing to messages)
import { Effect, PubSub } from "effect"
const program = Effect.gen(function*() {
const pubsub = yield* PubSub.bounded<string>(10)
// Subscribe within a scope for automatic cleanup
yield* Effect.scoped(Effect.gen(function*() {
const subscription = yield* PubSub.subscribe(pubsub)
// Publish some messages
yield* PubSub.publish(pubsub, "Hello")
yield* PubSub.publish(pubsub, "World")
// Take messages one by one
const msg1 = yield* PubSub.take(subscription)
const msg2 = yield* PubSub.take(subscription)
console.log(msg1, msg2) // "Hello", "World"
// Subscription is automatically cleaned up when scope exits
}))
yield* Effect.scoped(Effect.gen(function*() {
const sub1 = yield* PubSub.subscribe(pubsub)
const sub2 = yield* PubSub.subscribe(pubsub)
// Multiple subscribers can receive the same messages
yield* PubSub.publish(pubsub, "Broadcast")
const [msg1, msg2] = yield* Effect.all([
PubSub.take(sub1),
PubSub.take(sub2)
])
console.log("Both received:", msg1, msg2) // "Broadcast", "Broadcast"
}))
})
subscribe(pubsub: PubSub.PubSub<A>(parameter) pubsub: {
pubsub: PubSub.Atomic<A>;
subscribers: PubSub.Subscribers<A>;
scope: Scope.Closeable;
shutdownHook: Latch.Latch;
shutdownFlag: MutableRef.MutableRef<boolean>;
strategy: PubSub.Strategy<A>;
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; <…;
}
const fromSubscription: <A>(
subscription: PubSub.Subscription<A>
) => Channel<A>
Creates a channel from a PubSub subscription.
Example (Creating channels from subscriptions)
import { Channel, Data, Effect, PubSub } from "effect"
class SubscriptionError extends Data.TaggedError("SubscriptionError")<{
readonly reason: string
}> {}
const program = Effect.gen(function*() {
// Create a PubSub
const pubsub = yield* PubSub.bounded<string>(32)
// Create a subscription
const subscription = yield* PubSub.subscribe(pubsub)
// Publish some messages
yield* PubSub.publish(pubsub, "Hello")
yield* PubSub.publish(pubsub, "World")
yield* PubSub.publish(pubsub, "from")
yield* PubSub.publish(pubsub, "PubSub")
// Create a channel from the subscription
const channel = Channel.fromSubscription(subscription)
// The channel will receive all published messages
return channel
})
// Real-time notifications example
const notificationChannel = Effect.gen(function*() {
const eventBus = yield* PubSub.unbounded<{ type: string; payload: any }>()
const userSubscription = yield* PubSub.subscribe(eventBus)
return Channel.fromSubscription(userSubscription)
})
fromSubscription))