<A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(
self: Stream<A, E, R>
) => Stream<A2, E2 | E, R2 | R>
<A, E, R, A2, E2, R2>(
self: Stream<A, E, R>,
sink: Sink.Sink<A2, A, A, E2, R2>
): Stream<A2, E2 | E, R2 | R>Applies a sink transducer to the stream and emits each sink result.
Example (Transducing with a sink)
import { Console, Effect, Sink, Stream } from "effect"
const program = Effect.gen(function* () {
const result = yield* Stream.make(1, 2, 3, 4).pipe(
Stream.transduce(Sink.take(2)),
Stream.runCollect
)
yield* Console.log(result)
// Output: [ [ 1, 2 ], [ 3, 4 ] ]
})Aggregation
Source effect/Stream.ts:853146 lines
export const const transduce: (<A2, A, E2, R2>(
sink: Sink.Sink<A2, A, A, E2, R2>
) => <E, R>(
self: Stream<A, E, R>
) => Stream<A2, E2 | E, R2 | R>) &
(<A, E, R, A2, E2, R2>(
self: Stream<A, E, R>,
sink: Sink.Sink<A2, A, A, E2, R2>
) => Stream<A2, E2 | E, R2 | R>)
Applies a sink transducer to the stream and emits each sink result.
Example (Transducing with a sink)
import { Console, Effect, Sink, Stream } from "effect"
const program = Effect.gen(function* () {
const result = yield* Stream.make(1, 2, 3, 4).pipe(
Stream.transduce(Sink.take(2)),
Stream.runCollect
)
yield* Console.log(result)
// Output: [ [ 1, 2 ], [ 3, 4 ] ]
})
transduce = dual<<A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>) => <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>, <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>) => Stream<A2, E2 | E, R2 | R>>(arity: 2, body: <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>) => Stream<A2, E2 | E, R2 | R>): (<A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>) => <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>) & (<A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>) => Stream<A2, E2 | E, R2 | 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<
<function (type parameter) A2 in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>A2, function (type parameter) A in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>A, function (type parameter) E2 in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>E2, function (type parameter) R2 in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>R2>(
sink: Sink.Sink<A2, A, A, E2, R2>(parameter) sink: {
transform: (upstream: Pull.Pull<NonEmptyReadonlyArray<In>, never, void>, scope: Scope.Scope) => Effect.Effect<End<A, L>, E, 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; <…;
}
import SinkSink.interface Sink<out A, in In = unknown, out L = never, out E = never, out R = never>A Sink<A, In, L, E, R> is used to consume elements produced by a Stream.
You can think of a sink as a function that will consume a variable amount of
In elements (could be 0, 1, or many), might fail with an error of type E,
and will eventually yield a value of type A together with a remainder of
type L (i.e. any leftovers).
Example (Running a sink with a stream)
import { Effect, Sink, Stream } from "effect"
// Create a simple sink that always succeeds with a value
const sink: Sink.Sink<number> = Sink.succeed(42)
// Use the sink to consume a stream
const stream = Stream.make(1, 2, 3)
const program = Stream.run(stream, sink)
Effect.runPromise(program).then(console.log)
// Output: 42
Namespace containing types and interfaces for Sink variance and type relationships.
Sink<function (type parameter) A2 in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>A2, function (type parameter) A in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>A, function (type parameter) A in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>A, function (type parameter) E2 in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>E2, function (type parameter) R2 in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>R2>
) => <function (type parameter) E in <E, R>(self: Stream<A, E, R>): Stream<A2, E2 | E, R2 | R>E, function (type parameter) R in <E, R>(self: Stream<A, E, R>): Stream<A2, E2 | E, R2 | 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 <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>A, function (type parameter) E in <E, R>(self: Stream<A, E, R>): Stream<A2, E2 | E, R2 | R>E, function (type parameter) R in <E, R>(self: Stream<A, E, R>): Stream<A2, E2 | E, R2 | 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) A2 in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>A2, function (type parameter) E2 in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>E2 | function (type parameter) E in <E, R>(self: Stream<A, E, R>): Stream<A2, E2 | E, R2 | R>E, function (type parameter) R2 in <A2, A, E2, R2>(sink: Sink.Sink<A2, A, A, E2, R2>): <E, R>(self: Stream<A, E, R>) => Stream<A2, E2 | E, R2 | R>R2 | function (type parameter) R in <E, R>(self: Stream<A, E, R>): Stream<A2, E2 | E, R2 | R>R>,
<function (type parameter) A in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>R, function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | 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; <…;
}
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, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>R>,
sink: Sink.Sink<A2, A, A, E2, R2>(parameter) sink: {
transform: (upstream: Pull.Pull<NonEmptyReadonlyArray<In>, never, void>, scope: Scope.Scope) => Effect.Effect<End<A, L>, E, 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; <…;
}
import SinkSink.interface Sink<out A, in In = unknown, out L = never, out E = never, out R = never>A Sink<A, In, L, E, R> is used to consume elements produced by a Stream.
You can think of a sink as a function that will consume a variable amount of
In elements (could be 0, 1, or many), might fail with an error of type E,
and will eventually yield a value of type A together with a remainder of
type L (i.e. any leftovers).
Example (Running a sink with a stream)
import { Effect, Sink, Stream } from "effect"
// Create a simple sink that always succeeds with a value
const sink: Sink.Sink<number> = Sink.succeed(42)
// Use the sink to consume a stream
const stream = Stream.make(1, 2, 3)
const program = Stream.run(stream, sink)
Effect.runPromise(program).then(console.log)
// Output: 42
Namespace containing types and interfaces for Sink variance and type relationships.
Sink<function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A2, function (type parameter) A in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A, function (type parameter) A in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>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) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E2 | function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>R2 | function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>R>
>(
2,
<function (type parameter) A in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>R, function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | 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; <…;
}
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, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>R>,
sink: Sink.Sink<A2, A, A, E2, R2>(parameter) sink: {
transform: (upstream: Pull.Pull<NonEmptyReadonlyArray<In>, never, void>, scope: Scope.Scope) => Effect.Effect<End<A, L>, E, 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; <…;
}
import SinkSink.interface Sink<out A, in In = unknown, out L = never, out E = never, out R = never>A Sink<A, In, L, E, R> is used to consume elements produced by a Stream.
You can think of a sink as a function that will consume a variable amount of
In elements (could be 0, 1, or many), might fail with an error of type E,
and will eventually yield a value of type A together with a remainder of
type L (i.e. any leftovers).
Example (Running a sink with a stream)
import { Effect, Sink, Stream } from "effect"
// Create a simple sink that always succeeds with a value
const sink: Sink.Sink<number> = Sink.succeed(42)
// Use the sink to consume a stream
const stream = Stream.make(1, 2, 3)
const program = Stream.run(stream, sink)
Effect.runPromise(program).then(console.log)
// Output: 42
Namespace containing types and interfaces for Sink variance and type relationships.
Sink<function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A2, function (type parameter) A in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A, function (type parameter) A in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>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) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E2 | function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>R2 | function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>R> =>
const transformPull: <
A,
E,
R,
B,
E2,
R2,
EX,
RX
>(
self: Stream<A, E, R>,
f: (
pull: Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E,
void
>,
scope: Scope.Scope
) => Effect.Effect<
Pull.Pull<
Arr.NonEmptyReadonlyArray<B>,
E2,
void,
R2
>,
EX,
RX
>
) => Stream<
B,
EX | Pull.ExcludeDone<E2>,
R | R2 | RX
>
Derives a stream by transforming its pull effect.
Example (Transforming a pull effect)
import { Console, Effect, Stream } from "effect"
const stream = Stream.make(1, 2, 3)
const transformed = Stream.transformPull(stream, (pull) => Effect.succeed(pull))
const program = Effect.gen(function*() {
const values = yield* Stream.runCollect(transformed)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ 1, 2, 3 ]
transformPull(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; <…;
}
upstream: Pull.Pull<
readonly [A, ...A[]],
E,
void,
never
>
(parameter) upstream: {
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;
}
scope: Scope.Scope(parameter) scope: {
strategy: "sequential" | "parallel";
state: State.Open | State.Closed | State.Empty;
}
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 done:
| Exit.Exit<never, Cause.Done<void> | E>
| undefined
import ExitExit.type Exit<A, E = never> = Exit.Success<A, E> | Exit.Failure<A, E>Represents the result of an Effect computation.
When to use
Use when you need to synchronously inspect whether an Effect computation
succeeded or failed.
Details
An Exit<A, E> is either Success<A, E> containing a value of type A, or
Failure<A, E> containing a Cause<E> describing why the computation
failed.
Since Exit is also an Effect, you can yield it inside Effect.gen.
Example (Pattern matching on an Exit)
import { Exit } from "effect"
const success: Exit.Exit<number> = Exit.succeed(42)
const failure: Exit.Exit<number, string> = Exit.fail("error")
const result = Exit.match(success, {
onSuccess: (value) => `Got value: ${value}`,
onFailure: (cause) => `Got error: ${cause}`
})
Namespace containing helper types shared by Exit values.
When to use
Use to reference helper types that describe the shared structure of Exit
values.
Exit<never, import CauseCause.interface Done<A = void>A graceful completion signal for queues and streams.
When to use
Use to model normal producer completion through a stream or queue error
channel.
Details
Done indicates that a producer has finished normally — no more elements
will arrive. It is distinct from an error or interruption; it represents
successful completion. The optional value field can carry a final
leftover payload.
Example (Signaling queue completion)
import { Cause, Effect, Queue } from "effect"
const program = Effect.gen(function*() {
const queue = yield* Queue.bounded<number, Cause.Done>(10)
yield* Queue.offer(queue, 1)
yield* Queue.end(queue)
const result = yield* Effect.flip(Queue.take(queue))
console.log(Cause.isDone(result)) // true
})
Companion namespace for the Done interface.
Creates a Done signal with an optional value.
When to use
Use when you need to construct a low-level pull completion signal directly.
Done<void> | function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E> | undefined
let let leftover:
| Arr.NonEmptyReadonlyArray<A>
| undefined
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, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A> | undefined
const const upstreamWithLeftover: Effect.Effect<
readonly [A, ...A[]],
Cause.Done<void>,
never
>
const upstreamWithLeftover: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
import 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 leftover:
| Arr.NonEmptyReadonlyArray<A>
| undefined
var undefinedundefined) {
const const chunk: readonly [A, ...A[]]const chunk: {
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>;
}
let leftover:
| Arr.NonEmptyReadonlyArray<A>
| undefined
let leftover: {
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>;
}
let leftover:
| Arr.NonEmptyReadonlyArray<A>
| undefined
var undefinedundefined
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: readonly [A, ...A[]]const chunk: {
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>;
}
upstream: Pull.Pull<
readonly [A, ...A[]],
E,
void,
never
>
(parameter) upstream: {
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;
}
Pipeable.pipe<Effect.Effect<readonly [A, ...A[]], Cause.Done<void> | E, never>, Effect.Effect<readonly [A, ...A[]], Cause.Done<void>, never>>(this: Effect.Effect<readonly [A, ...A[]], Cause.Done<void> | E, never>, ab: (_: Effect.Effect<readonly [A, ...A[]], Cause.Done<void> | E, never>) => Effect.Effect<readonly [A, ...A[]], Cause.Done<void>, never>): Effect.Effect<readonly [A, ...A[]], Cause.Done<void>, never> (+21 overloads)pipe(
import EffectEffect.catch<Cause.Done<void> | E, never, Cause.Done<void>, never>(f: (e: Cause.Done<void> | E) => Effect.Effect<never, Cause.Done<void>, never>): <A, R>(self: Effect.Effect<A, Cause.Done<void> | E, R>) => Effect.Effect<A, Cause.Done<void>, R> (+1 overload)
export catch
error: Cause.Done<void> | Eerror) => {
let done:
| Exit.Exit<never, Cause.Done<void> | E>
| undefined
import ExitExit.const fail: <E>(e: E) => Exit<never, E>Creates a failed Exit from a typed error value.
When to use
Use when you need to represent an expected typed failure as an Exit.
Details
The error is wrapped in a Cause.Fail internally.
Returns a Failure<never, E>.
Example (Creating a failed Exit)
import { Exit } from "effect"
const exit = Exit.fail("Something went wrong")
console.log(Exit.isFailure(exit)) // true
fail(error: Cause.Done<void> | Eerror)
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 pull: Effect.Effect<
[A2, ...A2[]],
E2,
R2
>
const pull: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
import 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>
}
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(() => sink: Sink.Sink<A2, A, A, E2, R2>(parameter) sink: {
transform: (upstream: Pull.Pull<NonEmptyReadonlyArray<In>, never, void>, scope: Scope.Scope) => Effect.Effect<End<A, L>, E, 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; <…;
}
Sink<A2, A, A, E2, R2>.transform: (upstream: Pull.Pull<NonEmptyReadonlyArray<In>, never, void>, scope: Scope.Scope) => Effect.Effect<End<A, L>, E, R>transform(const upstreamWithLeftover: Effect.Effect<
readonly [A, ...A[]],
Cause.Done<void>,
never
>
const upstreamWithLeftover: {
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;
}
scope: Scope.Scope(parameter) scope: {
strategy: "sequential" | "parallel";
state: State.Open | State.Closed | State.Empty;
}
value: A2value, leftover_: readonly [A, ...A[]] | undefinedleftover_]) => {
let leftover:
| Arr.NonEmptyReadonlyArray<A>
| undefined
leftover_: readonly [A, ...A[]] | undefinedleftover_
return import ArrArr.const of: <A>(a: A) => NonEmptyArray<A>Wraps a single value in a NonEmptyArray.
Example (Creating a single-element array)
import { Array } from "effect"
console.log(Array.of(1)) // [1]
of(value: A2value)
}
)
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((): import PullPull.interface Pull<out A, out E = never, out Done = void, out R = never>An effectful pull step that either produces a value, fails with E, or
signals completion with Cause.Done<Done>.
When to use
Use to model one low-level pull step when a consumer repeatedly evaluates an
effect that may emit a value, fail normally, or signal normal completion
through Cause.Done.
Details
Pull represents completion in the error channel so low-level stream
consumers can distinguish ordinary failures from end-of-input and carry a
leftover value when needed.
Pull<
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) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>A2>,
function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E | function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>E2,
void,
function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, sink: Sink.Sink<A2, A, A, E2, R2>): Stream<A2, E2 | E, R2 | R>R2
> => let done:
| Exit.Exit<never, Cause.Done<void> | E>
| undefined
let done:
| Exit.Exit<never, Cause.Done<void> | E>
| undefined
const pull: Effect.Effect<
[A2, ...A2[]],
E2,
R2
>
const pull: {
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;
}