<A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>Runs the stream and returns the first element as an Option.
Example (Getting the first stream value)
import { Console, Effect, Option, Stream } from "effect"
const program = Effect.gen(function*() {
const head = yield* Stream.runHead(Stream.make(1, 2, 3))
yield* Console.log(Option.getOrThrow(head))
})
Effect.runPromise(program)
// 1destructors
Source effect/Stream.ts:108132 lines
export const const runHead: <A, E, R>(
self: Stream<A, E, R>
) => Effect.Effect<Option.Option<A>, E, R>
Runs the stream and returns the first element as an Option.
Example (Getting the first stream value)
import { Console, Effect, Option, Stream } from "effect"
const program = Effect.gen(function*() {
const head = yield* Stream.runHead(Stream.make(1, 2, 3))
yield* Console.log(Option.getOrThrow(head))
})
Effect.runPromise(program)
// 1
runHead = <function (type parameter) A in <A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>E, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>R>(self: Stream<A, E, R>(parameter) self: {
channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>;
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
}
interface Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>E, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>R>): import EffectEffect.type Effect.Effect = /*unresolved*/ anyEffect<import OptionOption.type Option.Option = /*unresolved*/ anyOption<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>A>, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>E, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Effect.Effect<Option.Option<A>, E, R>R> =>
import EffectEffect.map(import ChannelChannel.runHead(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; <…;
}
Stream<out A, out E = never, out R = never>.channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>(property) Stream<out A, out E = never, out R = never>.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; <…;
}
import OptionOption.map(import ArrArr.getUnsafe(0)))