<A>(options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?: "enforce" | "shape" | undefined
}): <E, R>(self: Stream<A, E, R>) => Stream<A, E, R>
<A, E, R>(
self: Stream<A, E, R>,
options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?: "enforce" | "shape" | undefined
}
): Stream<A, E, R>Rate-limits stream chunks with a synchronous cost function.
When to use
Use to throttle chunks when each chunk's cost can be computed synchronously.
Details
Uses a token bucket. The bucket can accumulate up to units + burst tokens,
and each chunk consumes the cost returned by cost.
If using the "enforce" strategy, arrays that do not meet the bandwidth constraints are dropped. If using the "shape" strategy, arrays are delayed until they can be emitted without exceeding the bandwidth constraints.
Defaults to the "shape" strategy.
Example (Throttling stream chunks)
import { Console, Effect, Schedule, Stream } from "effect"
const stream = Stream.fromSchedule(Schedule.spaced("50 millis")).pipe(
Stream.take(6),
Stream.throttle({
cost: (arr) => arr.length,
units: 1,
duration: "100 millis",
strategy: "shape"
})
)
const program = Effect.gen(function*() {
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
// Output: [ 0, 1, 2, 3, 4, 5 ]
})rate limiting
Source effect/Stream.ts:811935 lines
export const const throttle: {
<A>(options: {
readonly cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?:
| "enforce"
| "shape"
| undefined
}): <E, R>(
self: Stream<A, E, R>
) => Stream<A, E, R>
<A, E, R>(
self: Stream<A, E, R>,
options: {
readonly cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?:
| "enforce"
| "shape"
| undefined
}
): Stream<A, E, R>
}
Rate-limits stream chunks with a synchronous cost function.
When to use
Use to throttle chunks when each chunk's cost can be computed synchronously.
Details
Uses a token bucket. The bucket can accumulate up to units + burst tokens,
and each chunk consumes the cost returned by cost.
If using the "enforce" strategy, arrays that do not meet the bandwidth
constraints are dropped. If using the "shape" strategy, arrays are delayed
until they can be emitted without exceeding the bandwidth constraints.
Defaults to the "shape" strategy.
Example (Throttling stream chunks)
import { Console, Effect, Schedule, Stream } from "effect"
const stream = Stream.fromSchedule(Schedule.spaced("50 millis")).pipe(
Stream.take(6),
Stream.throttle({
cost: (arr) => arr.length,
units: 1,
duration: "100 millis",
strategy: "shape"
})
)
const program = Effect.gen(function*() {
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
// Output: [ 0, 1, 2, 3, 4, 5 ]
})
throttle: {
<function (type parameter) A in <A>(options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): <E, R>(self: Stream<A, E, R>) => Stream<A, E, R>
options: {
readonly cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?:
| "enforce"
| "shape"
| undefined
}
cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
arr: Arr.NonEmptyReadonlyArray<A>(parameter) arr: {
0: A;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
concat: { (...items: Array<ConcatArray<A>>): Array<A>; (...items: Array<A | ConcatArray<A>>): Array<A> };
join: (separator?: string) => string;
slice: (start?: number, end?: number) => Array<A>;
indexOf: (searchElement: A, fromIndex?: number) => number;
lastIndexOf: (searchElement: A, fromIndex?: number) => number;
every: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): this is readonly S[]; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => void, thisArg?: any) => void;
map: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): Array<S>; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): Array<A> };
reduce: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
reduceRight: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
find: { (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findIndex: (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
entries: () => ArrayIterator<[number, A]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<A>;
includes: (searchElement: A, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: A, index: number, array: Array<A>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => A | undefined;
findLast: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findLastIndex: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
toReversed: () => Array<A>;
toSorted: (compareFn?: ((a: A, b: A) => number) | undefined) => Array<A>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<A>): Array<A>; (start: number, deleteCount?: number): Array<A> };
with: (index: number, value: A) => Array<A>;
}
import ArrArr.type NonEmptyReadonlyArray<A> = readonly [
A,
...A[]
]
A readonly array guaranteed to have at least one element.
When to use
Use when non-emptiness must be tracked at the type level while preventing mutation.
Many Array module functions accept or return this type.
Example (Typing a non-empty array)
import type { Array } from "effect"
const nonEmpty: Array.NonEmptyReadonlyArray<number> = [1, 2, 3]
const head: number = nonEmpty[0] // guaranteed to exist
NonEmptyReadonlyArray<function (type parameter) A in <A>(options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): <E, R>(self: Stream<A, E, R>) => Stream<A, E, R>
units: numberunits: number
readonly duration: Duration.Inputduration: import DurationDuration.type Input =
| number
| bigint
| Duration.Duration
| readonly [seconds: number, nanos: number]
| `${number} nano`
| `${number} nanos`
| `${number} micro`
| `${number} micros`
| `${number} milli`
| `${number} millis`
| `${number} second`
| `${number} seconds`
| `${number} minute`
| `${number} minutes`
| `${number} hour`
| `${number} hours`
| `${number} day`
| `${number} days`
| `${number} week`
| `${number} weeks`
| "Infinity"
| "-Infinity"
| Duration.DurationObject
Valid input types that can be converted to a Duration.
When to use
Use when an API should accept any value that Effect can convert into a
Duration, including existing durations, millisecond numbers, nanosecond
bigints, high-resolution tuples, duration strings, infinity strings, or
duration objects.
Details
String inputs accept values like "10 seconds", "500 millis",
"Infinity", and "-Infinity". Finite fractional values that are
normalized to nanoseconds are rounded to the nearest nanosecond, with ties
away from zero.
Input
readonly burst?: number | undefinedburst?: number | undefined
readonly strategy?: "enforce" | "shape" | undefinedstrategy?: "enforce" | "shape" | undefined
}): <function (type parameter) E in <E, R>(self: Stream<A, E, R>): Stream<A, E, R>E, function (type parameter) R in <E, R>(self: Stream<A, E, R>): Stream<A, E, R>R>(self: Stream<A, E, R>(parameter) self: {
channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>;
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 Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A>(options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): <E, R>(self: Stream<A, E, R>) => Stream<A, E, R>
function (type parameter) E in <E, R>(self: Stream<A, E, R>): Stream<A, E, R>E, function (type parameter) R in <E, R>(self: Stream<A, E, R>): Stream<A, E, R>R>) => interface Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A>(options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): <E, R>(self: Stream<A, E, R>) => Stream<A, E, R>
function (type parameter) E in <E, R>(self: Stream<A, E, R>): Stream<A, E, R>E, function (type parameter) R in <E, R>(self: Stream<A, E, R>): Stream<A, E, R>R>
<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) E in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) R in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
self: Stream<A, E, R>(parameter) self: {
channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>;
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 Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) E in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) R in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
options: {
readonly cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?:
| "enforce"
| "shape"
| undefined
}
cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
arr: Arr.NonEmptyReadonlyArray<A>(parameter) arr: {
0: A;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
concat: { (...items: Array<ConcatArray<A>>): Array<A>; (...items: Array<A | ConcatArray<A>>): Array<A> };
join: (separator?: string) => string;
slice: (start?: number, end?: number) => Array<A>;
indexOf: (searchElement: A, fromIndex?: number) => number;
lastIndexOf: (searchElement: A, fromIndex?: number) => number;
every: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): this is readonly S[]; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => void, thisArg?: any) => void;
map: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): Array<S>; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): Array<A> };
reduce: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
reduceRight: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
find: { (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findIndex: (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
entries: () => ArrayIterator<[number, A]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<A>;
includes: (searchElement: A, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: A, index: number, array: Array<A>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => A | undefined;
findLast: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findLastIndex: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
toReversed: () => Array<A>;
toSorted: (compareFn?: ((a: A, b: A) => number) | undefined) => Array<A>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<A>): Array<A>; (start: number, deleteCount?: number): Array<A> };
with: (index: number, value: A) => Array<A>;
}
import ArrArr.type NonEmptyReadonlyArray<A> = readonly [
A,
...A[]
]
A readonly array guaranteed to have at least one element.
When to use
Use when non-emptiness must be tracked at the type level while preventing mutation.
Many Array module functions accept or return this type.
Example (Typing a non-empty array)
import type { Array } from "effect"
const nonEmpty: Array.NonEmptyReadonlyArray<number> = [1, 2, 3]
const head: number = nonEmpty[0] // guaranteed to exist
NonEmptyReadonlyArray<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
units: numberunits: number
readonly duration: Duration.Inputduration: import DurationDuration.type Input =
| number
| bigint
| Duration.Duration
| readonly [seconds: number, nanos: number]
| `${number} nano`
| `${number} nanos`
| `${number} micro`
| `${number} micros`
| `${number} milli`
| `${number} millis`
| `${number} second`
| `${number} seconds`
| `${number} minute`
| `${number} minutes`
| `${number} hour`
| `${number} hours`
| `${number} day`
| `${number} days`
| `${number} week`
| `${number} weeks`
| "Infinity"
| "-Infinity"
| Duration.DurationObject
Valid input types that can be converted to a Duration.
When to use
Use when an API should accept any value that Effect can convert into a
Duration, including existing durations, millisecond numbers, nanosecond
bigints, high-resolution tuples, duration strings, infinity strings, or
duration objects.
Details
String inputs accept values like "10 seconds", "500 millis",
"Infinity", and "-Infinity". Finite fractional values that are
normalized to nanoseconds are rounded to the nearest nanosecond, with ties
away from zero.
Input
readonly burst?: number | undefinedburst?: number | undefined
readonly strategy?: "enforce" | "shape" | undefinedstrategy?: "enforce" | "shape" | undefined
}
): interface Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) E in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) R in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
dual<(...args: Array<any>) => any, <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}) => Stream<A, E, R>>(arity: 2, body: <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}) => Stream<A, E, R>): ((...args: Array<any>) => any) & (<A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}) => Stream<A, E, R>) (+1 overload)
Creates a function that can be called in data-first style or data-last
(pipe-friendly) style.
When to use
Use to expose one implementation through both direct and pipe-friendly
call styles.
Details
Pass either the arity of the uncurried function or a predicate that decides
whether the current call is data-first. Arity is the common case. Use a
predicate when optional arguments make arity ambiguous.
Example (Selecting data-first or data-last style by arity)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(2, (self, that) => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Defining overloads with call signatures)
import { Function, pipe } from "effect"
const sum: {
(that: number): (self: number) => number
(self: number, that: number): number
} = Function.dual(2, (self: number, that: number): number => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Selecting data-first or data-last style with a predicate)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(
(args) => args.length === 2,
(self, that) => self + that
)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
dual(
2,
<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) E in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) R in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
self: Stream<A, E, R>(parameter) self: {
channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>;
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 Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) E in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) R in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
options: {
readonly cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?:
| "enforce"
| "shape"
| undefined
}
cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
arr: Arr.NonEmptyReadonlyArray<A>(parameter) arr: {
0: A;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
concat: { (...items: Array<ConcatArray<A>>): Array<A>; (...items: Array<A | ConcatArray<A>>): Array<A> };
join: (separator?: string) => string;
slice: (start?: number, end?: number) => Array<A>;
indexOf: (searchElement: A, fromIndex?: number) => number;
lastIndexOf: (searchElement: A, fromIndex?: number) => number;
every: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): this is readonly S[]; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => void, thisArg?: any) => void;
map: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): Array<S>; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): Array<A> };
reduce: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
reduceRight: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
find: { (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findIndex: (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
entries: () => ArrayIterator<[number, A]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<A>;
includes: (searchElement: A, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: A, index: number, array: Array<A>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => A | undefined;
findLast: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findLastIndex: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
toReversed: () => Array<A>;
toSorted: (compareFn?: ((a: A, b: A) => number) | undefined) => Array<A>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<A>): Array<A>; (start: number, deleteCount?: number): Array<A> };
with: (index: number, value: A) => Array<A>;
}
import ArrArr.type NonEmptyReadonlyArray<A> = readonly [
A,
...A[]
]
A readonly array guaranteed to have at least one element.
When to use
Use when non-emptiness must be tracked at the type level while preventing mutation.
Many Array module functions accept or return this type.
Example (Typing a non-empty array)
import type { Array } from "effect"
const nonEmpty: Array.NonEmptyReadonlyArray<number> = [1, 2, 3]
const head: number = nonEmpty[0] // guaranteed to exist
NonEmptyReadonlyArray<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
units: numberunits: number
readonly duration: Duration.Inputduration: import DurationDuration.type Input =
| number
| bigint
| Duration.Duration
| readonly [seconds: number, nanos: number]
| `${number} nano`
| `${number} nanos`
| `${number} micro`
| `${number} micros`
| `${number} milli`
| `${number} millis`
| `${number} second`
| `${number} seconds`
| `${number} minute`
| `${number} minutes`
| `${number} hour`
| `${number} hours`
| `${number} day`
| `${number} days`
| `${number} week`
| `${number} weeks`
| "Infinity"
| "-Infinity"
| Duration.DurationObject
Valid input types that can be converted to a Duration.
When to use
Use when an API should accept any value that Effect can convert into a
Duration, including existing durations, millisecond numbers, nanosecond
bigints, high-resolution tuples, duration strings, infinity strings, or
duration objects.
Details
String inputs accept values like "10 seconds", "500 millis",
"Infinity", and "-Infinity". Finite fractional values that are
normalized to nanoseconds are rounded to the nearest nanosecond, with ties
away from zero.
Input
readonly burst?: number | undefinedburst?: number | undefined
readonly strategy?: "enforce" | "shape" | undefinedstrategy?: "enforce" | "shape" | undefined
}
): interface Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) E in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
function (type parameter) R in <A, E, R>(self: Stream<A, E, R>, options: {
readonly cost: (arr: Arr.NonEmptyReadonlyArray<A>) => number;
readonly units: number;
readonly duration: Duration.Input;
readonly burst?: number | undefined;
readonly strategy?: "enforce" | "shape" | undefined;
}): Stream<A, E, R>
const throttleEffect: {
<A, E2, R2>(options: {
readonly cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => Effect.Effect<number, E2, R2>
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?:
| "enforce"
| "shape"
| undefined
}): <E, R>(
self: Stream<A, E, R>
) => Stream<A, E2 | E, R2 | R>
<A, E, R, E2, R2>(
self: Stream<A, E, R>,
options: {
readonly cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => Effect.Effect<number, E2, R2>
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?:
| "enforce"
| "shape"
| undefined
}
): Stream<A, E | E2, R | R2>
}
self: Stream<A, E, R>(parameter) self: {
channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>;
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; <…;
}
options: {
readonly cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?:
| "enforce"
| "shape"
| undefined
}
cost: (
arr: readonly [A, ...A[]]
) => Effect.Effect<number, never, never>
arr: readonly [A, ...A[]](parameter) arr: {
0: A;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
concat: { (...items: Array<ConcatArray<A>>): Array<A>; (...items: Array<A | ConcatArray<A>>): Array<A> };
join: (separator?: string) => string;
slice: (start?: number, end?: number) => Array<A>;
indexOf: (searchElement: A, fromIndex?: number) => number;
lastIndexOf: (searchElement: A, fromIndex?: number) => number;
every: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): this is readonly S[]; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => void, thisArg?: any) => void;
map: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): Array<S>; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): Array<A> };
reduce: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
reduceRight: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
find: { (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findIndex: (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
entries: () => ArrayIterator<[number, A]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<A>;
includes: (searchElement: A, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: A, index: number, array: Array<A>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => A | undefined;
findLast: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findLastIndex: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
toReversed: () => Array<A>;
toSorted: (compareFn?: ((a: A, b: A) => number) | undefined) => Array<A>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<A>): Array<A>; (start: number, deleteCount?: number): Array<A> };
with: (index: number, value: A) => Array<A>;
}
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(options: {
readonly cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
readonly units: number
readonly duration: Duration.Input
readonly burst?: number | undefined
readonly strategy?:
| "enforce"
| "shape"
| undefined
}
cost: (
arr: Arr.NonEmptyReadonlyArray<A>
) => number
arr: readonly [A, ...A[]](parameter) arr: {
0: A;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
concat: { (...items: Array<ConcatArray<A>>): Array<A>; (...items: Array<A | ConcatArray<A>>): Array<A> };
join: (separator?: string) => string;
slice: (start?: number, end?: number) => Array<A>;
indexOf: (searchElement: A, fromIndex?: number) => number;
lastIndexOf: (searchElement: A, fromIndex?: number) => number;
every: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): this is readonly S[]; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => void, thisArg?: any) => void;
map: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): Array<S>; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): Array<A> };
reduce: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
reduceRight: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
find: { (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findIndex: (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
entries: () => ArrayIterator<[number, A]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<A>;
includes: (searchElement: A, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: A, index: number, array: Array<A>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => A | undefined;
findLast: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findLastIndex: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
toReversed: () => Array<A>;
toSorted: (compareFn?: ((a: A, b: A) => number) | undefined) => Array<A>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<A>): Array<A>; (start: number, deleteCount?: number): Array<A> };
with: (index: number, value: A) => Array<A>;
}