<A, E>(self: Pool<A, E>): Effect.Effect<A, E, Scope.Scope>Retrieves an item from the pool in a scoped effect.
When to use
Use to borrow a pooled resource for the lifetime of the current scope so it is automatically returned when that scope closes.
Details
The returned effect waits for an available item when the pool is at capacity. If acquiring a new item fails, the effect fails with the acquisition error.
Gotchas
Retrying a failed get can repeat the acquisition attempt.
export const const get: <A, E>(
self: Pool<A, E>
) => Effect.Effect<A, E, Scope.Scope>
Retrieves an item from the pool in a scoped effect.
When to use
Use to borrow a pooled resource for the lifetime of the current scope so it
is automatically returned when that scope closes.
Details
The returned effect waits for an available item when the pool is at capacity.
If acquiring a new item fails, the effect fails with the acquisition error.
Gotchas
Retrying a failed get can repeat the acquisition attempt.
get = <function (type parameter) A in <A, E>(self: Pool<A, E>): Effect.Effect<A, E, Scope.Scope>A, function (type parameter) E in <A, E>(self: Pool<A, E>): Effect.Effect<A, E, Scope.Scope>E>(self: Pool<A, E>(parameter) self: {
config: Config<A, E>;
state: State<A, 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; <…;
}
interface Pool<in out A, in out E = never>A Pool<A, E> is a pool of items of type A, each of which may be
associated with the acquisition and release of resources. An attempt to get
an item A from a pool may fail with an error of type E.
When to use
Use when you need to share a bounded set of scoped resources across fibers
while the pool manages acquisition, reuse, and release.
Pool<function (type parameter) A in <A, E>(self: Pool<A, E>): Effect.Effect<A, E, Scope.Scope>A, function (type parameter) E in <A, E>(self: Pool<A, E>): Effect.Effect<A, E, Scope.Scope>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: Pool<A, E>): Effect.Effect<A, E, Scope.Scope>A, function (type parameter) E in <A, E>(self: Pool<A, E>): Effect.Effect<A, E, Scope.Scope>E, import ScopeScope.Scope> =>
import EffectEffect.const suspend: <A, E, R>(
effect: LazyArg<Effect<A, E, R>>
) => Effect<A, E, R>
Creates an Effect lazily, delaying construction until it is needed.
When to use
Use when you need to defer the evaluation of an effect until it is required.
Details
suspend takes a thunk that represents an effect and delays creating it
until the suspended effect is evaluated. This is useful for optimizing
expensive computations, managing circular dependencies such as recursive
functions, and helping TypeScript unify return types when branches construct
different effects. Any side effects or scoped captures inside the thunk are
re-executed on each invocation.
Example (Lazily evaluating side effects)
import { Effect } from "effect"
let i = 0
const bad = Effect.succeed(i++)
const good = Effect.suspend(() => Effect.succeed(i++))
console.log(Effect.runSync(bad)) // Output: 0
console.log(Effect.runSync(bad)) // Output: 0
console.log(Effect.runSync(good)) // Output: 1
console.log(Effect.runSync(good)) // Output: 2
Example (Suspending recursive Fibonacci evaluation)
import { Effect } from "effect"
const blowsUp = (n: number): Effect.Effect<number> =>
n < 2
? Effect.succeed(1)
: Effect.zipWith(blowsUp(n - 1), blowsUp(n - 2), (a, b) => a + b)
// console.log(Effect.runSync(blowsUp(32)))
// crash: JavaScript heap out of memory
const allGood = (n: number): Effect.Effect<number> =>
n < 2
? Effect.succeed(1)
: Effect.zipWith(
Effect.suspend(() => allGood(n - 1)),
Effect.suspend(() => allGood(n - 2)),
(a, b) => a + b
)
console.log(Effect.runSync(allGood(32)))
// Output: 3524578
Example (Helping TypeScript infer recursive effect types)
import { Effect } from "effect"
// Without suspend, TypeScript may struggle with type inference.
// Inferred type:
// (a: number, b: number) =>
// Effect<never, Error, never> | Effect<number, never, never>
const withoutSuspend = (a: number, b: number) =>
b === 0
? Effect.fail(new Error("Cannot divide by zero"))
: Effect.succeed(a / b)
// Using suspend to unify return types.
// Inferred type:
// (a: number, b: number) => Effect<number, Error, never>
const withSuspend = (a: number, b: number) =>
Effect.suspend(() =>
b === 0
? Effect.fail(new Error("Cannot divide by zero"))
: Effect.succeed(a / b)
)
suspend(() => {
if (self: Pool<A, E>(parameter) self: {
config: Config<A, E>;
state: State<A, 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; <…;
}
Pool<A, E>.state: State<A, E>(property) Pool<A, E>.state: {
scope: Scope.Scope;
isShuttingDown: boolean;
semaphore: Semaphore.Semaphore;
resizeSemaphore: Semaphore.Semaphore;
items: Set<PoolItem<A, E>>;
available: Set<PoolItem<A, E>>;
availableLatch: Latch.Latch;
invalidated: Set<PoolItem<A, E>>;
waiters: number;
}
State<A, E>.isShuttingDown: booleanisShuttingDown) {
return import EffectEffect.const interrupt: Effect<never>const interrupt: {
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;
}
Returns an effect that is immediately interrupted.
Example (Creating an interrupted effect)
import { Effect } from "effect"
const program = Effect.gen(function*() {
return yield* Effect.interrupt
yield* Effect.succeed("This won't execute and is unreachable")
})
Effect.runPromise(program).catch(console.error)
// Throws: InterruptedException
interrupt
}
return 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>
}
const getPoolItem: <A, E>(
self: Pool<A, E>
) => Effect.Effect<
PoolItem<A, E>,
never,
Scope.Scope
>
self: Pool<A, E>(parameter) self: {
config: Config<A, E>;
state: State<A, 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; <…;
}
item: PoolItem<A, E>(parameter) item: {
exit: Exit.Exit<A, E>;
finalizer: Effect.Effect<void>;
refCount: number;
disableReclaim: boolean;
}
item: PoolItem<A, E>(parameter) item: {
exit: Exit.Exit<A, E>;
finalizer: Effect.Effect<void>;
refCount: number;
disableReclaim: boolean;
}
PoolItem<A, E>.exit: Exit.Exit<A, E>exit)
})