(min: number, max: number, chunkSize?: number): Stream<number>Constructs a stream from a range of integers, including both endpoints.
Details
If the provided min is greater than max, the stream will not emit any
values.
Example (Creating a numeric range)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const values = yield* Stream.range(1, 5).pipe(Stream.runCollect)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ 1, 2, 3, 4, 5 ]constructors
Source effect/Stream.ts:175721 lines
export const const range: (
min: number,
max: number,
chunkSize?: number
) => Stream<number>
Constructs a stream from a range of integers, including both endpoints.
Details
If the provided min is greater than max, the stream will not emit any
values.
Example (Creating a numeric range)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const values = yield* Stream.range(1, 5).pipe(Stream.runCollect)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ 1, 2, 3, 4, 5 ]
range = (
min: numbermin: number,
max: numbermax: number,
chunkSize: numberchunkSize = import ChannelChannel.const DefaultChunkSize: numberThe default chunk size used by channels for batching operations.
Example (Reading the default chunk size)
import { Channel } from "effect"
console.log(Channel.DefaultChunkSize) // 4096
DefaultChunkSize
): 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<number> =>
min: numbermin > max: numbermax ? const empty: Stream<never>const empty: {
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; <…;
}
Creates an empty stream.
Example (Creating an empty stream)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const values = yield* Stream.empty.pipe(Stream.runCollect)
yield* Console.log(values)
})
Effect.runPromise(program)
// []
empty : const fromPull: <A, E, R, EX, RX>(
pull: Effect.Effect<
Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E,
void,
R
>,
EX,
RX
>
) => Stream<A, Pull.ExcludeDone<E> | EX, R | RX>
Creates a stream from a pull effect, such as one produced by Stream.toPull.
Details
A pull effect yields chunks on demand and completes when the upstream stream ends.
See Stream.toPull for a matching producer.
Example (Creating a stream from a pull effect)
import { Console, Effect, Stream } from "effect"
const program = Effect.scoped(
Effect.gen(function*() {
const source = Stream.make(1, 2, 3)
const pull = yield* Stream.toPull(source)
const stream = Stream.fromPull(Effect.succeed(pull))
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
})
)
Effect.runPromise(program)
// Output: [1, 2, 3]
fromPull(import EffectEffect.const sync: <A>(
thunk: LazyArg<A>
) => Effect<A>
Creates an Effect that represents a synchronous side-effectful computation.
When to use
Use when you need to wrap a synchronous side-effectful operation that is not
expected to throw.
Details
The provided function is evaluated lazily when the effect runs.
Gotchas
The function must not throw. If it throws, the thrown value is treated as a
defect, not as a typed failure. Use try when throwing is expected.
Example (Capturing synchronous logging in an Effect)
import { Effect } from "effect"
const log = (message: string) =>
Effect.sync(() => {
console.log(message) // side effect
})
// ┌─── Effect<void, never, never>
// ▼
const program = log("Hello, World!")
sync(() => {
let let start: numberstart = min: numbermin
let let done: booleandone = false
return 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 (let done: booleandone) return import CauseCause.const done: <A = void>(
value?: A
) => Effect.Effect<never, Done<A>>
Creates an Effect that fails with a Done error. Shorthand for
Effect.fail(Cause.Done(value)).
When to use
Use when you model stream or queue completion through the error channel.
Example (Failing with Done)
import { Cause, Effect } from "effect"
const program = Cause.done("finished")
Effect.runPromiseExit(program).then((exit) => {
console.log(exit._tag) // "Failure"
})
done()
const const remaining: numberremaining = max: numbermax - let start: numberstart + 1
if (const remaining: numberremaining > chunkSize: numberchunkSize) {
const const chunk: [number, ...number[]]const chunk: {
0: number;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
pop: () => number | undefined;
push: (...items: Array<number>) => number;
concat: { (...items: Array<ConcatArray<number>>): Array<number>; (...items: Array<number | ConcatArray<number>>): Array<number> };
join: (separator?: string) => string;
reverse: () => Array<number>;
shift: () => number | undefined;
slice: (start?: number, end?: number) => Array<number>;
sort: (compareFn?: ((a: number, b: number) => number) | undefined) => [number, ...number[]];
splice: { (start: number, deleteCount?: number): Array<number>; (start: number, deleteCount: number, ...items: Array<number>): Array<number> };
unshift: (...items: Array<number>) => number;
indexOf: (searchElement: number, fromIndex?: number) => number;
lastIndexOf: (searchElement: number, fromIndex?: number) => number;
every: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: number, index: number, array: Array<number>) => void, thisArg?: any) => void;
map: (callbackfn: (value: number, index: number, array: Array<number>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): Array<S>; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): Array<number> };
reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number, …;
reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number, …;
find: { (predicate: (value: number, index: number, obj: Array<number>) => value is S, thisArg?: any): S | undefined; (predicate: (value: number, index: number, obj: Array<number>) => unknown, thisArg?: any): number | undefined };
findIndex: (predicate: (value: number, index: number, obj: Array<number>) => unknown, thisArg?: any) => number;
fill: (value: number, start?: number, end?: number) => [number, ...number[]];
copyWithin: (target: number, start: number, end?: number) => [number, ...number[]];
entries: () => ArrayIterator<[number, number]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<number>;
includes: (searchElement: number, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: number, index: number, array: Array<number>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => number | undefined;
findLast: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): S | undefined; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): number | undefined };
findLastIndex: (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any) => number;
toReversed: () => Array<number>;
toSorted: (compareFn?: ((a: number, b: number) => number) | undefined) => Array<number>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<number>): Array<number>; (start: number, deleteCount?: number): Array<number> };
with: (index: number, value: number) => Array<number>;
}
import ArrArr.const range: (
start: number,
end: number
) => NonEmptyArray<number>
Creates a NonEmptyArray containing a range of integers, inclusive on both
ends.
When to use
Use when you need a non-empty sequence of consecutive integers.
Details
If start > end, returns [start].
Example (Creating a range)
import { Array } from "effect"
const result = Array.range(1, 3)
console.log(result) // [1, 2, 3]
range(let start: numberstart, let start: numberstart + chunkSize: numberchunkSize - 1)
let start: numberstart += chunkSize: numberchunkSize
return 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(const chunk: [number, ...number[]]const chunk: {
0: number;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
pop: () => number | undefined;
push: (...items: Array<number>) => number;
concat: { (...items: Array<ConcatArray<number>>): Array<number>; (...items: Array<number | ConcatArray<number>>): Array<number> };
join: (separator?: string) => string;
reverse: () => Array<number>;
shift: () => number | undefined;
slice: (start?: number, end?: number) => Array<number>;
sort: (compareFn?: ((a: number, b: number) => number) | undefined) => [number, ...number[]];
splice: { (start: number, deleteCount?: number): Array<number>; (start: number, deleteCount: number, ...items: Array<number>): Array<number> };
unshift: (...items: Array<number>) => number;
indexOf: (searchElement: number, fromIndex?: number) => number;
lastIndexOf: (searchElement: number, fromIndex?: number) => number;
every: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: number, index: number, array: Array<number>) => void, thisArg?: any) => void;
map: (callbackfn: (value: number, index: number, array: Array<number>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): Array<S>; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): Array<number> };
reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number, …;
reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number, …;
find: { (predicate: (value: number, index: number, obj: Array<number>) => value is S, thisArg?: any): S | undefined; (predicate: (value: number, index: number, obj: Array<number>) => unknown, thisArg?: any): number | undefined };
findIndex: (predicate: (value: number, index: number, obj: Array<number>) => unknown, thisArg?: any) => number;
fill: (value: number, start?: number, end?: number) => [number, ...number[]];
copyWithin: (target: number, start: number, end?: number) => [number, ...number[]];
entries: () => ArrayIterator<[number, number]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<number>;
includes: (searchElement: number, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: number, index: number, array: Array<number>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => number | undefined;
findLast: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): S | undefined; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): number | undefined };
findLastIndex: (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any) => number;
toReversed: () => Array<number>;
toSorted: (compareFn?: ((a: number, b: number) => number) | undefined) => Array<number>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<number>): Array<number>; (start: number, deleteCount?: number): Array<number> };
with: (index: number, value: number) => Array<number>;
}
const chunk: [number, ...number[]]const chunk: {
0: number;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
pop: () => number | undefined;
push: (...items: Array<number>) => number;
concat: { (...items: Array<ConcatArray<number>>): Array<number>; (...items: Array<number | ConcatArray<number>>): Array<number> };
join: (separator?: string) => string;
reverse: () => Array<number>;
shift: () => number | undefined;
slice: (start?: number, end?: number) => Array<number>;
sort: (compareFn?: ((a: number, b: number) => number) | undefined) => [number, ...number[]];
splice: { (start: number, deleteCount?: number): Array<number>; (start: number, deleteCount: number, ...items: Array<number>): Array<number> };
unshift: (...items: Array<number>) => number;
indexOf: (searchElement: number, fromIndex?: number) => number;
lastIndexOf: (searchElement: number, fromIndex?: number) => number;
every: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: number, index: number, array: Array<number>) => void, thisArg?: any) => void;
map: (callbackfn: (value: number, index: number, array: Array<number>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): Array<S>; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): Array<number> };
reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number, …;
reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number, …;
find: { (predicate: (value: number, index: number, obj: Array<number>) => value is S, thisArg?: any): S | undefined; (predicate: (value: number, index: number, obj: Array<number>) => unknown, thisArg?: any): number | undefined };
findIndex: (predicate: (value: number, index: number, obj: Array<number>) => unknown, thisArg?: any) => number;
fill: (value: number, start?: number, end?: number) => [number, ...number[]];
copyWithin: (target: number, start: number, end?: number) => [number, ...number[]];
entries: () => ArrayIterator<[number, number]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<number>;
includes: (searchElement: number, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: number, index: number, array: Array<number>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => number | undefined;
findLast: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): S | undefined; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): number | undefined };
findLastIndex: (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any) => number;
toReversed: () => Array<number>;
toSorted: (compareFn?: ((a: number, b: number) => number) | undefined) => Array<number>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<number>): Array<number>; (start: number, deleteCount?: number): Array<number> };
with: (index: number, value: number) => Array<number>;
}
import ArrArr.const range: (
start: number,
end: number
) => NonEmptyArray<number>
Creates a NonEmptyArray containing a range of integers, inclusive on both
ends.
When to use
Use when you need a non-empty sequence of consecutive integers.
Details
If start > end, returns [start].
Example (Creating a range)
import { Array } from "effect"
const result = Array.range(1, 3)
console.log(result) // [1, 2, 3]
range(let start: numberstart, let start: numberstart + const remaining: numberremaining - 1)
let done: booleandone = true
return 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(const chunk: [number, ...number[]]const chunk: {
0: number;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
pop: () => number | undefined;
push: (...items: Array<number>) => number;
concat: { (...items: Array<ConcatArray<number>>): Array<number>; (...items: Array<number | ConcatArray<number>>): Array<number> };
join: (separator?: string) => string;
reverse: () => Array<number>;
shift: () => number | undefined;
slice: (start?: number, end?: number) => Array<number>;
sort: (compareFn?: ((a: number, b: number) => number) | undefined) => [number, ...number[]];
splice: { (start: number, deleteCount?: number): Array<number>; (start: number, deleteCount: number, ...items: Array<number>): Array<number> };
unshift: (...items: Array<number>) => number;
indexOf: (searchElement: number, fromIndex?: number) => number;
lastIndexOf: (searchElement: number, fromIndex?: number) => number;
every: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: number, index: number, array: Array<number>) => void, thisArg?: any) => void;
map: (callbackfn: (value: number, index: number, array: Array<number>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): Array<S>; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): Array<number> };
reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number, …;
reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: Array<number>) => number, …;
find: { (predicate: (value: number, index: number, obj: Array<number>) => value is S, thisArg?: any): S | undefined; (predicate: (value: number, index: number, obj: Array<number>) => unknown, thisArg?: any): number | undefined };
findIndex: (predicate: (value: number, index: number, obj: Array<number>) => unknown, thisArg?: any) => number;
fill: (value: number, start?: number, end?: number) => [number, ...number[]];
copyWithin: (target: number, start: number, end?: number) => [number, ...number[]];
entries: () => ArrayIterator<[number, number]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<number>;
includes: (searchElement: number, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: number, index: number, array: Array<number>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => number | undefined;
findLast: { (predicate: (value: number, index: number, array: Array<number>) => value is S, thisArg?: any): S | undefined; (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any): number | undefined };
findLastIndex: (predicate: (value: number, index: number, array: Array<number>) => unknown, thisArg?: any) => number;
toReversed: () => Array<number>;
toSorted: (compareFn?: ((a: number, b: number) => number) | undefined) => Array<number>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<number>): Array<number>; (start: number, deleteCount?: number): Array<number> };
with: (index: number, value: number) => Array<number>;
}