<A, E>(self: TxDequeue<A, E>): Effect.Effect<Option.Option<A>>Tries to take an item from the queue without blocking.
Example (Polling without blocking)
import { Effect, Option, TxQueue } from "effect"
const program = Effect.gen(function*() {
const queue = yield* TxQueue.bounded<number>(10)
// Poll returns Option.none if empty
const maybe = yield* TxQueue.poll(queue)
console.log(Option.isNone(maybe)) // true
yield* TxQueue.offer(queue, 42)
const item = yield* TxQueue.poll(queue)
console.log(Option.getOrNull(item)) // 42
})export const const poll: <A, E>(
self: TxDequeue<A, E>
) => Effect.Effect<Option.Option<A>>
Tries to take an item from the queue without blocking.
Example (Polling without blocking)
import { Effect, Option, TxQueue } from "effect"
const program = Effect.gen(function*() {
const queue = yield* TxQueue.bounded<number>(10)
// Poll returns Option.none if empty
const maybe = yield* TxQueue.poll(queue)
console.log(Option.isNone(maybe)) // true
yield* TxQueue.offer(queue, 42)
const item = yield* TxQueue.poll(queue)
console.log(Option.getOrNull(item)) // 42
})
poll = <function (type parameter) A in <A, E>(self: TxDequeue<A, E>): Effect.Effect<Option.Option<A>>A, function (type parameter) E in <A, E>(self: TxDequeue<A, E>): Effect.Effect<Option.Option<A>>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<Option.Option<A>>A, function (type parameter) E in <A, E>(self: TxDequeue<A, E>): Effect.Effect<Option.Option<A>>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<import OptionOption.type Option<A> = Option.None<A> | Option.Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) A in <A, E>(self: TxDequeue<A, E>): Effect.Effect<Option.Option<A>>A>> =>
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 import OptionOption.const none: <A = never>() => Option<A>Creates an Option representing the absence of a value.
When to use
Use to represent a missing or uninitialized value, such as returning "no
result" from a function.
Details
- Returns
Option<never>, which is a subtype of Option<A> for any A
- Always returns the same singleton instance
Example (Creating an empty Option)
import { Option } from "effect"
// ┌─── Option<never>
// ▼
const noValue = Option.none()
console.log(noValue)
// Output: { _id: 'Option', _tag: 'None' }
none()
}
const 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 import OptionOption.const none: <A = never>() => Option<A>Creates an Option representing the absence of a value.
When to use
Use to represent a missing or uninitialized value, such as returning "no
result" from a function.
Details
- Returns
Option<never>, which is a subtype of Option<A> for any A
- Always returns the same singleton instance
Example (Creating an empty Option)
import { Option } from "effect"
// ┌─── Option<never>
// ▼
const noValue = Option.none()
console.log(noValue)
// Output: { _id: 'Option', _tag: 'None' }
none()
}
yield* import TxChunkTxChunk.const drop: {
(n: number): <A>(
self: TxChunk<A>
) => Effect.Effect<void>
<A>(
self: TxChunk<A>,
n: number
): Effect.Effect<void>
}
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; <…;
}
import OptionOption.const some: <A>(value: A) => Option<A>Wraps the given value into an Option to represent its presence.
When to use
Use to wrap a known present value as Option
- Returning a successful result from a partial function
Details
- Always returns
Some<A>
- Does not filter
null or undefined; use
fromNullishOr
for that
Example (Wrapping a value)
import { Option } from "effect"
// ┌─── Option<number>
// ▼
const value = Option.some(1)
console.log(value)
// Output: { _id: 'Option', _tag: 'Some', value: 1 }
some(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<Option.None<any> | Option.Some<any>, never, never>, Effect.Effect<Option.None<any> | Option.Some<any>, never, never>>(this: Effect.Effect<Option.None<any> | Option.Some<any>, never, never>, ab: (_: Effect.Effect<Option.None<any> | Option.Some<any>, never, never>) => Effect.Effect<Option.None<any> | Option.Some<any>, never, never>): Effect.Effect<Option.None<any> | Option.Some<any>, never, 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)