<A, E2, R2>(
predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>
): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>
<A, E, R, E2, R2>(
self: Stream<A, E, R>,
predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>
): Stream<A, E | E2, R | R2>Takes elements from the stream while the effectful predicate is true.
When to use
Use when the leading-prefix predicate needs an Effect or service and the stream should stop before the first false result.
Example (Effectfully taking while a predicate holds)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const result = yield* Stream.range(1, 5).pipe(
Stream.takeWhileEffect((n) => Effect.succeed(n % 3 !== 0)),
Stream.runCollect
)
Console.log(result)
})
Effect.runPromise(program)
// Output: [ 1, 2 ]export const const takeWhileEffect: {
<A, E2, R2>(
predicate: (
a: NoInfer<A>,
n: number
) => Effect.Effect<boolean, E2, R2>
): <E, R>(
self: Stream<A, E, R>
) => Stream<A, E | E2, R | R2>
<A, E, R, E2, R2>(
self: Stream<A, E, R>,
predicate: (
a: NoInfer<A>,
n: number
) => Effect.Effect<boolean, E2, R2>
): Stream<A, E | E2, R | R2>
}
Takes elements from the stream while the effectful predicate is true.
When to use
Use when the leading-prefix predicate needs an Effect or service and the
stream should stop before the first false result.
Example (Effectfully taking while a predicate holds)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const result = yield* Stream.range(1, 5).pipe(
Stream.takeWhileEffect((n) => Effect.succeed(n % 3 !== 0)),
Stream.runCollect
)
Console.log(result)
})
Effect.runPromise(program)
// Output: [ 1, 2 ]
takeWhileEffect: {
<function (type parameter) A in <A, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>A, function (type parameter) E2 in <A, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>R2>(
predicate: (
a: NoInfer<A>,
n: number
) => Effect.Effect<boolean, E2, R2>
a: NoInfer<A>a: type NoInfer<A> = [A][A extends any ? 0 : never]Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) A in <A, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>A>, n: numbern: number) => 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<boolean, function (type parameter) E2 in <A, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>R2>
): <function (type parameter) E in <E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R | R2>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, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>A, function (type parameter) E in <E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R | R2>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, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>A, function (type parameter) E in <E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R | R2>E | function (type parameter) E2 in <A, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>E2, function (type parameter) R in <E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R | R2>R | function (type parameter) R2 in <A, E2, R2>(predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R | R2>R2>
<function (type parameter) A in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>R, function (type parameter) E2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>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; <…;
}
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, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>R>,
predicate: (
a: NoInfer<A>,
n: number
) => Effect.Effect<boolean, E2, R2>
a: NoInfer<A>a: type NoInfer<A> = [A][A extends any ? 0 : never]Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) A in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>A>, n: numbern: number) => 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<boolean, function (type parameter) E2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>R2>
): 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, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>R2>
} = dual<(...args: Array<any>) => any, <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>) => Stream<A, E | E2, R | R2>>(arity: 2, body: <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>) => Stream<A, E | E2, R | R2>): ((...args: Array<any>) => any) & (<A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>) => Stream<A, E | E2, R | R2>) (+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, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>R, function (type parameter) E2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>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; <…;
}
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, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>R>,
predicate: (
a: NoInfer<A>,
n: number
) => Effect.Effect<boolean, E2, R2>
a: NoInfer<A>a: type NoInfer<A> = [A][A extends any ? 0 : never]Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) A in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>A>, n: numbern: number) => 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<boolean, function (type parameter) E2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, E2, R2>(self: Stream<A, E, R>, predicate: (a: NoInfer<A>, n: number) => Effect.Effect<boolean, E2, R2>): Stream<A, E | E2, R | R2>R2>
) =>
const takeUntilEffect: {
<A, E2, R2>(
predicate: (
a: NoInfer<A>,
n: number
) => Effect.Effect<boolean, E2, R2>,
options?: {
readonly excludeLast?: boolean | undefined
}
): <E, R>(
self: Stream<A, E, R>
) => Stream<A, E2 | E, R2 | R>
<A, E, R, E2, R2>(
self: Stream<A, E, R>,
predicate: (
a: A,
n: number
) => Effect.Effect<boolean, E2, R2>,
options?: {
readonly excludeLast?: boolean | 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; <…;
}
a: Aa, n: numbern) =>
import EffectEffect.const map: {
<A, B>(f: (a: A) => B): <E, R>(
self: Effect<A, E, R>
) => Effect<B, E, R>
<A, E, R, B>(
self: Effect<A, E, R>,
f: (a: A) => B
): Effect<B, E, R>
}
predicate: (
a: NoInfer<A>,
n: number
) => Effect.Effect<boolean, E2, R2>
a: Aa, n: numbern),
(b: booleanb) => !b: booleanb
), { excludeLast?: boolean | undefinedexcludeLast: true }))