<E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(
refinement: Refinement<NoInfer<E>, EB>,
f: (e: EB) => Stream<A2, E2, R2>,
orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined
): <A, R>(
self: Stream<A, E, R>
) => Stream<
A | A2 | Exclude<A3, unassigned>,
E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never),
R | R2 | R3
>
<E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(
predicate: Predicate<NoInfer<E>>,
f: (e: NoInfer<E>) => Stream<A2, E2, R2>,
orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined
): <A, R>(
self: Stream<A, E, R>
) => Stream<
A | A2 | Exclude<A3, unassigned>,
E2 | E3 | (A3 extends unassigned ? E : never),
R | R2 | R3
>
<
A,
E,
R,
EB extends E,
A2,
E2,
R2,
A3 = unassigned,
E3 = never,
R3 = never
>(
self: Stream<A, E, R>,
refinement: Refinement<E, EB>,
f: (e: EB) => Stream<A2, E2, R2>,
orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined
): Stream<
A | A2 | Exclude<A3, unassigned>,
E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never),
R | R2 | R3
>
<A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(
self: Stream<A, E, R>,
predicate: Predicate<E>,
f: (e: E) => Stream<A2, E2, R2>,
orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined
): Stream<
A | A2 | Exclude<A3, unassigned>,
E2 | E3 | (A3 extends unassigned ? E : never),
R | R2 | R3
>Recovers from errors that match a predicate by switching to a recovery stream.
Details
When a failure matches the filter, the stream switches to the recovery stream. Non-matching failures propagate downstream, so the error type is preserved unless the filter narrows it.
Example (Catching matching failures)
import { Console, Effect, Stream } from "effect"
const stream = Stream.make(1, 2).pipe(
Stream.concat(Stream.fail(42)),
Stream.catchIf(
(error): error is 42 => error === 42,
() => Stream.make(999)
)
)
const program = Effect.gen(function*() {
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
// Output: [ 1, 2, 999 ]
})
Effect.runPromise(program)error handling
Source effect/Stream.ts:512451 lines
export const const catchIf: {
<
E,
EB extends E,
A2,
E2,
R2,
A3 = unassigned,
E3 = never,
R3 = never
>(
refinement: Refinement<NoInfer<E>, EB>,
f: (e: EB) => Stream<A2, E2, R2>,
orElse?:
| ((
e: Exclude<E, EB>
) => Stream<A3, E3, R3>)
| undefined
): <A, R>(
self: Stream<A, E, R>
) => Stream<
A | A2 | Exclude<A3, unassigned>,
| E2
| E3
| (A3 extends unassigned
? Exclude<E, EB>
: never),
R | R2 | R3
>
<
E,
A2,
E2,
R2,
A3 = unassigned,
E3 = never,
R3 = never
>(
predicate: Predicate<NoInfer<E>>,
f: (e: NoInfer<E>) => Stream<A2, E2, R2>,
orElse?:
| ((e: NoInfer<E>) => Stream<A3, E3, R3>)
| undefined
): <A, R>(
self: Stream<A, E, R>
) => Stream<
A | A2 | Exclude<A3, unassigned>,
E2 | E3 | (A3 extends unassigned ? E : never),
R | R2 | R3
>
<
A,
E,
R,
EB extends E,
A2,
E2,
R2,
A3 = unassigned,
E3 = never,
R3 = never
>(
self: Stream<A, E, R>,
refinement: Refinement<E, EB>,
f: (e: EB) => Stream<A2, E2, R2>,
orElse?:
| ((
e: Exclude<E, EB>
) => Stream<A3, E3, R3>)
| undefined
): Stream<
A | A2 | Exclude<A3, unassigned>,
| E2
| E3
| (A3 extends unassigned
? Exclude<E, EB>
: never),
R | R2 | R3
>
<
A,
E,
R,
A2,
E2,
R2,
A3 = unassigned,
E3 = never,
R3 = never
>(
self: Stream<A, E, R>,
predicate: Predicate<E>,
f: (e: E) => Stream<A2, E2, R2>,
orElse?:
| ((e: E) => Stream<A3, E3, R3>)
| undefined
): Stream<
A | A2 | Exclude<A3, unassigned>,
E2 | E3 | (A3 extends unassigned ? E : never),
R | R2 | R3
>
}
Recovers from errors that match a predicate by switching to a recovery stream.
Details
When a failure matches the filter, the stream switches to the recovery
stream. Non-matching failures propagate downstream, so the error type is
preserved unless the filter narrows it.
Example (Catching matching failures)
import { Console, Effect, Stream } from "effect"
const stream = Stream.make(1, 2).pipe(
Stream.concat(Stream.fail(42)),
Stream.catchIf(
(error): error is 42 => error === 42,
() => Stream.make(999)
)
)
const program = Effect.gen(function*() {
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
// Output: [ 1, 2, 999 ]
})
Effect.runPromise(program)
catchIf: {
<function (type parameter) E in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) EB in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB extends function (type parameter) E in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) A2 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A2, function (type parameter) E2 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E2, function (type parameter) R2 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R2, function (type parameter) A3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A3 = unassigned, function (type parameter) E3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E3 = never, function (type parameter) R3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R3 = never>(
refinement: Refinement<NoInfer<E>, EB>refinement: interface Refinement<in A, out B extends A>A predicate that also narrows the input type when it returns true.
When to use
Use when you want a runtime check that refines A to B for TypeScript,
especially when composing type guards with
compose
or safely
checking unknown values.
Details
A refinement returns a type predicate (a is B). Use it with if or
filter to narrow types.
Example (Narrowing unknown values)
import { Predicate } from "effect"
const isString: Predicate.Refinement<unknown, string> = (u): u is string => typeof u === "string"
const data: unknown = "hello"
if (isString(data)) {
console.log(data.toUpperCase())
}
Type-level utilities for working with
Refinement
types.
When to use
Use when you need to extract input and output types from refinement
signatures while writing generic helpers over refinements.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting refinement types)
import { Predicate } from "effect"
type IsString = Predicate.Refinement<unknown, string>
type Input = Predicate.Refinement.In<IsString>
type Output = Predicate.Refinement.Out<IsString>
Refinement<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) E in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E>, function (type parameter) EB in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB>,
f: (e: EB) => Stream<A2, E2, R2>f: (e: EB extends Ee: function (type parameter) EB in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB) => 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 <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A2, function (type parameter) E2 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E2, function (type parameter) R2 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R2>,
orElse: | ((e: Exclude<E, EB>) => Stream<A3, E3, R3>)
| undefined
e: Exclude<E, EB>e: type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) E in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) EB in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB>) => 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) A3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A3, function (type parameter) E3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E3, function (type parameter) R3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R3>) | undefined
): <function (type parameter) A in <A, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A, function (type parameter) R in <A, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>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, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A, function (type parameter) E in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) R in <A, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>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, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A | function (type parameter) A2 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A2 | type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) A3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A3, unassigned>, function (type parameter) E2 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E2 | function (type parameter) E3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E3 | (function (type parameter) A3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A3 extends unassigned ? type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) E in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) EB in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB> : never), function (type parameter) R in <A, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R | function (type parameter) R2 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R2 | function (type parameter) R3 in <E, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(refinement: Refinement<NoInfer<E>, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R3>
<function (type parameter) E in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E, function (type parameter) A2 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A2, function (type parameter) E2 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E2, function (type parameter) R2 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R2, function (type parameter) A3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A3 = unassigned, function (type parameter) E3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E3 = never, function (type parameter) R3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R3 = never>(
predicate: Predicate<NoInfer<E>>predicate: interface Predicate<in A>A function that decides whether a value of type A satisfies a condition.
When to use
Use when you want a reusable boolean check for A, especially when you plan
to combine checks with
and
/
or
or pass a predicate to arrays
and iterables.
Details
A predicate returns true or false and never throws by itself. It does not
narrow types unless you use Refinement.
Example (Defining a predicate)
import { Predicate } from "effect"
const isPositive: Predicate.Predicate<number> = (n) => n > 0
console.log(isPositive(1))
Type-level utilities for working with
Predicate
types.
When to use
Use when you need to extract input types from predicate signatures while
writing generic helpers over predicate types.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting predicate input)
import { Predicate } from "effect"
type IsString = Predicate.Predicate<string>
type Input = Predicate.Predicate.In<IsString>
Predicate<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) E in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E>>,
f: (e: NoInfer<E>) => Stream<A2, E2, R2>f: (e: NoInfer<E>e: 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) E in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E>) => 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 <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A2, function (type parameter) E2 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E2, function (type parameter) R2 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R2>,
orElse: | ((e: NoInfer<E>) => Stream<A3, E3, R3>)
| undefined
e: NoInfer<E>e: 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) E in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E>) => 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) A3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A3, function (type parameter) E3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E3, function (type parameter) R3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R3>) | undefined
): <function (type parameter) A in <A, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A, function (type parameter) R in <A, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>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, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A, function (type parameter) E in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E, function (type parameter) R in <A, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>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, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A | function (type parameter) A2 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A2 | type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) A3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A3, unassigned>, function (type parameter) E2 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E2 | function (type parameter) E3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E3 | (function (type parameter) A3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A3 extends unassigned ? function (type parameter) E in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E : never), function (type parameter) R in <A, R>(self: Stream<A, E, R>): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R | function (type parameter) R2 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R2 | function (type parameter) R3 in <E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(predicate: Predicate<NoInfer<E>>, f: (e: NoInfer<E>) => Stream<A2, E2, R2>, orElse?: ((e: NoInfer<E>) => Stream<A3, E3, R3>) | undefined): <A, R>(self: Stream<A, E, R>) => Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R3>
<function (type parameter) A in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A, function (type parameter) E in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) R in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R, function (type parameter) EB in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB extends function (type parameter) E in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) A2 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E2, function (type parameter) R2 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R2, function (type parameter) A3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A3 = unassigned, function (type parameter) E3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E3 = never, function (type parameter) R3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R3 = never>(
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, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A, function (type parameter) E in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) R in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R>,
refinement: Refinement<E, EB>refinement: interface Refinement<in A, out B extends A>A predicate that also narrows the input type when it returns true.
When to use
Use when you want a runtime check that refines A to B for TypeScript,
especially when composing type guards with
compose
or safely
checking unknown values.
Details
A refinement returns a type predicate (a is B). Use it with if or
filter to narrow types.
Example (Narrowing unknown values)
import { Predicate } from "effect"
const isString: Predicate.Refinement<unknown, string> = (u): u is string => typeof u === "string"
const data: unknown = "hello"
if (isString(data)) {
console.log(data.toUpperCase())
}
Type-level utilities for working with
Refinement
types.
When to use
Use when you need to extract input and output types from refinement
signatures while writing generic helpers over refinements.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting refinement types)
import { Predicate } from "effect"
type IsString = Predicate.Refinement<unknown, string>
type Input = Predicate.Refinement.In<IsString>
type Output = Predicate.Refinement.Out<IsString>
Refinement<function (type parameter) E in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) EB in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB>,
f: (e: EB) => Stream<A2, E2, R2>f: (e: EB extends Ee: function (type parameter) EB in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB) => 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, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E2, function (type parameter) R2 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R2>,
orElse: | ((e: Exclude<E, EB>) => Stream<A3, E3, R3>)
| undefined
e: Exclude<E, EB>e: type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) E in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) EB in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB>) => 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) A3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A3, function (type parameter) E3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E3, function (type parameter) R3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R3>) | undefined
): interface Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A | function (type parameter) A2 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A2 | type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) A3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A3, unassigned>, function (type parameter) E2 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E2 | function (type parameter) E3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E3 | (function (type parameter) A3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>A3 extends unassigned ? type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) E in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>E, function (type parameter) EB in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>EB> : never), function (type parameter) R in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R | function (type parameter) R2 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R2 | function (type parameter) R3 in <A, E, R, EB extends E, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, refinement: Refinement<E, EB>, f: (e: EB) => Stream<A2, E2, R2>, orElse?: ((e: Exclude<E, EB>) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? Exclude<E, EB> : never), R | R2 | R3>R3>
<function (type parameter) A in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A, function (type parameter) E in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E, function (type parameter) R in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R, function (type parameter) A2 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R2, function (type parameter) A3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A3 = unassigned, function (type parameter) E3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E3 = never, function (type parameter) R3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R3 = never>(
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, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A, function (type parameter) E in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E, function (type parameter) R in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R>,
predicate: Predicate<E>predicate: interface Predicate<in A>A function that decides whether a value of type A satisfies a condition.
When to use
Use when you want a reusable boolean check for A, especially when you plan
to combine checks with
and
/
or
or pass a predicate to arrays
and iterables.
Details
A predicate returns true or false and never throws by itself. It does not
narrow types unless you use Refinement.
Example (Defining a predicate)
import { Predicate } from "effect"
const isPositive: Predicate.Predicate<number> = (n) => n > 0
console.log(isPositive(1))
Type-level utilities for working with
Predicate
types.
When to use
Use when you need to extract input types from predicate signatures while
writing generic helpers over predicate types.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting predicate input)
import { Predicate } from "effect"
type IsString = Predicate.Predicate<string>
type Input = Predicate.Predicate.In<IsString>
Predicate<function (type parameter) E in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E>,
f: (e: E) => Stream<A2, E2, R2>f: (e: Ee: function (type parameter) E in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E) => 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, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R2>,
orElse: | ((e: E) => Stream<A3, E3, R3>)
| undefined
e: Ee: function (type parameter) E in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E) => 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) A3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A3, function (type parameter) E3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E3, function (type parameter) R3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R3>) | undefined
): interface Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A | function (type parameter) A2 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A2 | type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) A3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A3, unassigned>, function (type parameter) E2 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E2 | function (type parameter) E3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E3 | (function (type parameter) A3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>A3 extends unassigned ? function (type parameter) E in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>E : never), function (type parameter) R in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R | function (type parameter) R2 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R2 | function (type parameter) R3 in <A, E, R, A2, E2, R2, A3 = unassigned, E3 = never, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (e: E) => Stream<A2, E2, R2>, orElse?: ((e: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | Exclude<A3, unassigned>, E2 | E3 | (A3 extends unassigned ? E : never), R | R2 | R3>R3>
} = dual<(...args: Array<any>) => any, <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined) => Stream<A | A2 | A3, E2 | E3, R | R2 | R3>>(isDataFirst: (args: IArguments) => boolean, body: <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined) => Stream<A | A2 | A3, E2 | E3, R | R2 | R3>): ((...args: Array<any>) => any) & (<A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined) => Stream<A | A2 | A3, E2 | E3, R | R2 | R3>) (+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((args: IArgumentsargs) => const isStream: (
u: unknown
) => u is Stream<unknown, unknown, unknown>
Checks whether a value is a Stream.
Example (Checking whether a value is a Stream)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const stream = Stream.make(1, 2, 3)
const notStream = { data: [1, 2, 3] }
yield* Console.log(Stream.isStream(stream))
// true
yield* Console.log(Stream.isStream(notStream))
// false
})
Effect.runPromise(program)
isStream(args: IArgumentsargs[0]), <
function (type parameter) A in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>A,
function (type parameter) E in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E,
function (type parameter) R in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>R,
function (type parameter) A2 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>A2,
function (type parameter) E2 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E2,
function (type parameter) R2 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>R2,
function (type parameter) A3 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>A3 = never,
function (type parameter) E3 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E3 = function (type parameter) E in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E,
function (type parameter) R3 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>R3 = never
>(
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, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>A, function (type parameter) E in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E, function (type parameter) R in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>R>,
predicate: Predicate<E>predicate: interface Predicate<in A>A function that decides whether a value of type A satisfies a condition.
When to use
Use when you want a reusable boolean check for A, especially when you plan
to combine checks with
and
/
or
or pass a predicate to arrays
and iterables.
Details
A predicate returns true or false and never throws by itself. It does not
narrow types unless you use Refinement.
Example (Defining a predicate)
import { Predicate } from "effect"
const isPositive: Predicate.Predicate<number> = (n) => n > 0
console.log(isPositive(1))
Type-level utilities for working with
Predicate
types.
When to use
Use when you need to extract input types from predicate signatures while
writing generic helpers over predicate types.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting predicate input)
import { Predicate } from "effect"
type IsString = Predicate.Predicate<string>
type Input = Predicate.Predicate.In<IsString>
Predicate<function (type parameter) E in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E>,
f: (failure: E) => Stream<A2, E2, R2>f: (failure: Efailure: function (type parameter) E in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E) => 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, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>R2>,
orElse: | ((failure: E) => Stream<A3, E3, R3>)
| undefined
failure: Efailure: function (type parameter) E in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E) => 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) A3 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>A3, function (type parameter) E3 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E3, function (type parameter) R3 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>R3>) | undefined
): interface Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>A | function (type parameter) A2 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>A2 | function (type parameter) A3 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>A3, function (type parameter) E2 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E2 | function (type parameter) E3 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>E3, function (type parameter) R in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>R | function (type parameter) R2 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>R2 | function (type parameter) R3 in <A, E, R, A2, E2, R2, A3 = never, E3 = E, R3 = never>(self: Stream<A, E, R>, predicate: Predicate<E>, f: (failure: E) => Stream<A2, E2, R2>, orElse?: ((failure: E) => Stream<A3, E3, R3>) | undefined): Stream<A | A2 | A3, E2 | E3, R | R2 | R3>R3> =>
const fromChannel: <
Arr extends Arr.NonEmptyReadonlyArray<any>,
E,
R
>(
channel: Channel.Channel<
Arr,
E,
void,
unknown,
unknown,
unknown,
R
>
) => Stream<
Arr extends Arr.NonEmptyReadonlyArray<infer A>
? A
: never,
E,
R
>
Creates a stream from a array-emitting Channel.
Example (Creating a stream from an array-emitting channel)
import { Channel, Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const channel = Channel.succeed([1, 2, 3] as const)
const stream = Stream.fromChannel(channel)
const result = yield* Stream.runCollect(stream)
yield* Console.log(result)
})
// Output: [ 1, 2, 3 ]
fromChannel(
import ChannelChannel.const catchIf: <readonly [A, ...A[]], E, void, unknown, unknown, unknown, R, readonly [A2, ...A2[]], E2, void, unknown, unknown, unknown, R2, readonly [A3, ...A3[]], E3, void, unknown, unknown, unknown, R3>(self: Channel.Channel<readonly [A, ...A[]], E, void, unknown, unknown, unknown, R>, predicate: Predicate<E>, f: (failure: E) => Channel.Channel<readonly [A2, ...A2[]], E2, void, unknown, unknown, unknown, R2>, orElse?: ((failure: E) => Channel.Channel<readonly [A3, ...A3[]], E3, void, unknown, unknown, unknown, R3>) | undefined) => Channel.Channel<readonly [A, ...A[]] | readonly [A2, ...A2[]] | readonly [A3, ...A3[]], E2 | E3, void, unknown, unknown, unknown, R | R2 | R3> (+3 overloads)catchIf(
const toChannel: <A, E, R>(
stream: Stream<A, E, R>
) => Channel.Channel<
Arr.NonEmptyReadonlyArray<A>,
E,
void,
unknown,
unknown,
unknown,
R
>
Creates a channel from a stream.
Example (Converting a stream to a channel)
import { Channel, Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const stream = Stream.make(1, 2, 3)
const channel = Stream.toChannel(stream)
const values = yield* Channel.runCollect(channel)
yield* Console.log(values.flat())
})
Effect.runPromise(program)
// Output: [ 1, 2, 3 ]
toChannel(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; <…;
}
predicate: Predicate<E>predicate,
(e: Ee) => f: (failure: E) => Stream<A2, E2, R2>f(e: Ee).Stream<A2, E2, R2>.channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>(property) Stream<A2, E2, R2>.channel: {
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; <…;
}
orElse: | ((failure: E) => Stream<A3, E3, R3>)
| undefined
e: Ee) => orElse: | ((failure: E) => Stream<A3, E3, R3>)
| undefined
e: Ee).Stream<A3, E3, R3>.channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>(property) Stream<A3, E3, R3>.channel: {
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; <…;
}
Referenced by 1 symbols