<A, E>(self: TxDequeue<A, E>): Effect.Effect<A, E>Waits transactionally for the next item and returns it without removing it.
Details
If the queue is open but empty, the transaction retries until an item is available or the queue completes. If the queue is done, the queue's completion cause is propagated through the error channel.
Example (Peeking without removing values)
import { Effect, TxQueue } from "effect"
const program = Effect.gen(function*() {
const queue = yield* TxQueue.bounded<number, string>(10)
yield* TxQueue.offer(queue, 42)
// Peek at the next item without removing it
const item = yield* TxQueue.peek(queue)
console.log(item) // 42
// Item is still in the queue
const size = yield* TxQueue.size(queue)
console.log(size) // 1
})
// Error handling example
const errorExample = Effect.gen(function*() {
const queue = yield* TxQueue.bounded<number, string>(5)
yield* TxQueue.fail(queue, "queue failed")
// peek() propagates the queue error through E-channel
const result = yield* Effect.flip(TxQueue.peek(queue))
console.log(result) // "queue failed"
})export const const peek: <A, E>(
self: TxDequeue<A, E>
) => Effect.Effect<A, E>
Waits transactionally for the next item and returns it without removing it.
Details
If the queue is open but empty, the transaction retries until an item is available or the queue completes. If the queue is done, the queue's completion cause is propagated through the error channel.
Example (Peeking without removing values)
import { Effect, TxQueue } from "effect"
const program = Effect.gen(function*() {
const queue = yield* TxQueue.bounded<number, string>(10)
yield* TxQueue.offer(queue, 42)
// Peek at the next item without removing it
const item = yield* TxQueue.peek(queue)
console.log(item) // 42
// Item is still in the queue
const size = yield* TxQueue.size(queue)
console.log(size) // 1
})
// Error handling example
const errorExample = Effect.gen(function*() {
const queue = yield* TxQueue.bounded<number, string>(5)
yield* TxQueue.fail(queue, "queue failed")
// peek() propagates the queue error through E-channel
const result = yield* Effect.flip(TxQueue.peek(queue))
console.log(result) // "queue failed"
})
peek = <function (type parameter) A in <A, E>(self: TxDequeue<A, E>): Effect.Effect<A, E>A, function (type parameter) E in <A, E>(self: TxDequeue<A, E>): Effect.Effect<A, E>E>(self: TxDequeue<A, E>(parameter) self: {
strategy: "bounded" | "unbounded" | "dropping" | "sliding";
capacity: number;
items: TxChunk.TxChunk<any>;
stateRef: TxRef.TxRef<State<any, any>>;
toString: () => string;
toJSON: () => unknown;
}
interface TxDequeue<out A, out E = never>Namespace containing type definitions for TxDequeue variance annotations.
A TxDequeue represents the read-only interface of a transactional queue, providing
operations for consuming elements (dequeue operations) and inspecting queue state.
Example (Taking values through dequeue handles)
import { Effect, TxQueue } from "effect"
const program = Effect.gen(function*() {
// Queue without error channel
const queue = yield* TxQueue.bounded<number>(10)
yield* TxQueue.offer(queue, 42)
const item = yield* TxQueue.take(queue)
console.log(item) // 42
// Queue with error channel - errors propagate through E-channel
const faultTolerantQueue = yield* TxQueue.bounded<number, string>(10)
yield* TxQueue.fail(faultTolerantQueue, "processing failed")
// All dequeue operations now fail with the error directly
const takeResult = yield* Effect.flip(TxQueue.take(faultTolerantQueue)) // "processing failed"
const peekResult = yield* Effect.flip(TxQueue.peek(faultTolerantQueue)) // "processing failed"
})
TxDequeue<function (type parameter) A in <A, E>(self: TxDequeue<A, E>): Effect.Effect<A, E>A, function (type parameter) E in <A, E>(self: TxDequeue<A, E>): Effect.Effect<A, E>E>): 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>(self: TxDequeue<A, E>): Effect.Effect<A, E>A, function (type parameter) E in <A, E>(self: TxDequeue<A, E>): Effect.Effect<A, E>E> =>
import EffectEffect.const gen: {
<Eff extends Effect<any, any, any>, AEff>(
f: () => Generator<Eff, AEff, never>
): Effect<
AEff,
[Eff] extends [never]
? never
: [Eff] extends [
Effect<infer _A, infer E, infer _R>
]
? E
: never,
[Eff] extends [never]
? never
: [Eff] extends [
Effect<infer _A, infer _E, infer R>
]
? R
: never
>
<Self, Eff extends Effect<any, any, any>, AEff>(
options: { readonly self: Self },
f: (this: Self) => Generator<Eff, AEff, never>
): Effect<
AEff,
[Eff] extends [never]
? never
: [Eff] extends [
Effect<infer _A, infer E, infer _R>
]
? E
: never,
[Eff] extends [never]
? never
: [Eff] extends [
Effect<infer _A, infer _E, infer R>
]
? R
: never
>
}
const state: State<any, any>state = yield* import TxRefTxRef.const get: <A>(
self: TxRef<A>
) => Effect.Effect<A>
Reads the current value of the TxRef.
When to use
Use to read the current value of a TxRef.
Example (Reading transactional references)
import { Effect, TxRef } from "effect"
const program = Effect.gen(function*() {
const counter = yield* TxRef.make(42)
// Read the value within a transaction
const value = yield* Effect.tx(
TxRef.get(counter)
)
console.log(value) // 42
})
get(self: TxDequeue<A, E>(parameter) self: {
strategy: "bounded" | "unbounded" | "dropping" | "sliding";
capacity: number;
items: TxChunk.TxChunk<any>;
stateRef: TxRef.TxRef<State<any, any>>;
toString: () => string;
toJSON: () => unknown;
}
TxQueueState.stateRef: TxRef.TxRef<State<any, any>>(property) TxQueueState.stateRef: {
version: number;
pending: Map<unknown, () => void>;
value: 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 state: State<any, any>state._tag: "Open" | "Closing" | "Done"_tag === "Done") {
return yield* import EffectEffect.const failCause: <E>(
cause: Cause.Cause<E>
) => Effect<never, E>
Creates an Effect that represents a failure with a specific Cause.
When to use
Use when you already have a full Cause and need to preserve defects,
interruptions, annotations, or combined failures in the effect's failure
channel.
Details
This function allows you to create effects that fail with complex error
structures, including multiple errors, defects, interruptions, and more.
Example (Failing with a full Cause)
import { Cause, Effect } from "effect"
const program = Effect.failCause(
Cause.fail("Network error")
)
Effect.runPromiseExit(program).then(console.log)
// Output: { _id: 'Exit', _tag: 'Failure', cause: ... }
failCause(const state: {
readonly _tag: "Done"
readonly cause: Cause.Cause<any>
}
cause: Cause.Cause<E>(property) cause: {
reasons: ReadonlyArray<Reason<E>>;
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;
}
const chunk: Chunk.Chunk<any>const chunk: {
length: number;
right: Chunk<A>;
left: Chunk<A>;
backing: Backing<A>;
depth: number;
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 TxChunkTxChunk.const get: <A>(
self: TxChunk<A>
) => Effect.Effect<Chunk.Chunk<A>>
Reads the current chunk from the TxChunk.
Example (Reading the current chunk)
import { Chunk, Effect, TxChunk } from "effect"
const program = Effect.gen(function*() {
const txChunk = yield* TxChunk.fromIterable([1, 2, 3])
// Read the current value within a transaction
const chunk = yield* TxChunk.get(txChunk)
console.log(Chunk.toReadonlyArray(chunk)) // [1, 2, 3]
// The value is tracked for conflict detection
const size = Chunk.size(chunk)
console.log(size) // 3
})
get(self: TxDequeue<A, E>(parameter) self: {
strategy: "bounded" | "unbounded" | "dropping" | "sliding";
capacity: number;
items: TxChunk.TxChunk<any>;
stateRef: TxRef.TxRef<State<any, any>>;
toString: () => string;
toJSON: () => unknown;
}
TxQueueState.items: TxChunk.TxChunk<any>(property) TxQueueState.items: {
ref: TxRef.TxRef<Chunk.Chunk<A>>;
toString: () => string;
toJSON: () => unknown;
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 head: Option.Option<any>head = import ChunkChunk.const head: <A>(
self: Chunk<A>
) => Option<A>
Returns the first element of this chunk safely if it exists.
Example (Getting the first element)
import { Chunk } from "effect"
console.log(Chunk.head(Chunk.empty())) // { _tag: "None" }
console.log(Chunk.head(Chunk.make(1, 2, 3))) // { _tag: "Some", value: 1 }
head(const chunk: Chunk.Chunk<any>const chunk: {
length: number;
right: Chunk<A>;
left: Chunk<A>;
backing: Backing<A>;
depth: number;
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 OptionOption.const isNone: <A>(
self: Option<A>
) => self is None<A>
Checks whether an Option is None (absent).
When to use
Use when you need to branch on an absent Option before accessing .value.
Details
- Acts as a type guard, narrowing to
None<A>
Example (Checking for None)
import { Option } from "effect"
console.log(Option.isNone(Option.some(1)))
// Output: false
console.log(Option.isNone(Option.none()))
// Output: true
isNone(const head: Option.Option<any>head)) {
return yield* import EffectEffect.const txRetry: Effect<
never,
never,
Transaction
>
const txRetry: {
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;
}
Retries the current transaction by signaling that it must be retried.
Details
NOTE: the transaction retries on any change to transactional values (i.e. TxRef) accessed in its body.
Example (Retrying transactions)
import { Effect, TxRef } from "effect"
const program = Effect.gen(function*() {
// create a transactional reference
const ref = yield* TxRef.make(0)
// forks a fiber that increases the value of `ref` every 100 millis
yield* Effect.forkChild(Effect.forever(
// update to transactional value
Effect.tx(TxRef.update(ref, (n) => n + 1)).pipe(Effect.delay("100 millis"))
))
// the following will retry 10 times until the `ref` value is 10
yield* Effect.tx(Effect.gen(function*() {
const value = yield* TxRef.get(ref)
if (value < 10) {
yield* Effect.log(`retry due to value: ${value}`)
return yield* Effect.txRetry
}
yield* Effect.log(`transaction done with value: ${value}`)
}))
})
Effect.runPromise(program).catch(console.error)
txRetry
}
return const head: Option.Some<any>const head: {
_tag: "Some";
_op: "Some";
value: A;
valueOrUndefined: 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; <…;
toString: () => string;
toJSON: () => unknown;
}
Some<any>.value: anyvalue
}).Pipeable.pipe<Effect.Effect<any, any, Effect.Transaction>, Effect.Effect<any, any, never>>(this: Effect.Effect<any, any, Effect.Transaction>, ab: (_: Effect.Effect<any, any, Effect.Transaction>) => Effect.Effect<any, any, never>): Effect.Effect<any, any, never> (+21 overloads)pipe(import EffectEffect.const tx: <A, E, R>(
effect: Effect<A, E, R>
) => Effect<A, E, Exclude<R, Transaction>>
Defines a transaction boundary. Transactions are "all or nothing" with respect to changes
made to transactional values (i.e. TxRef) that occur within the transaction body.
Details
If called inside an active transaction, tx composes with the current transaction and reuses
its journal and retry state instead of creating a nested boundary.
Effect transactions are optimistic with retry. A transaction is retried when
its body explicitly calls Effect.txRetry and any accessed transactional
value changes, or when any accessed transactional value changes because a
different transaction commits before the current one.
The outermost tx call creates the transaction boundary and commits or rolls back the full
composed transaction.
Example (Running a transaction)
import { Effect, TxRef } from "effect"
const program = Effect.gen(function*() {
const ref1 = yield* TxRef.make(0)
const ref2 = yield* TxRef.make(0)
// Nested tx calls compose into the same transaction
yield* Effect.tx(Effect.gen(function*() {
yield* TxRef.set(ref1, 10)
yield* Effect.tx(TxRef.set(ref2, 20))
const sum = (yield* TxRef.get(ref1)) + (yield* TxRef.get(ref2))
console.log(`Transaction sum: ${sum}`)
}))
console.log(`Final ref1: ${yield* TxRef.get(ref1)}`) // 10
console.log(`Final ref2: ${yield* TxRef.get(ref2)}`) // 20
})
tx)