effect-io-ai

Package: effect
Module: Stream

Stream.mergeLeft

Merges two streams while emitting only the values from the left stream.

When to use

Use when the right stream is needed for its effects or failures, but downstream consumers should only receive values from the left stream.

Details

The right stream still runs for its effects, and any failures from the right stream are propagated. The merged stream completes when the left stream completes, interrupting the right stream.

Example (Merging streams while keeping left values)

import { Console, Effect, Stream } from "effect"

const program = Effect.gen(function*() {
  const left = Stream.make(1, 2)
  const right = Stream.make("a", "b")
  const values = yield* left.pipe(Stream.mergeLeft(right), Stream.runCollect)
  yield* Console.log(values)
})

Effect.runPromise(program)
// Output: [ 1, 2 ]

Signature

declare const mergeLeft: { <AR, ER, RR>(right: Stream<AR, ER, RR>): <AL, EL, RL>(left: Stream<AL, EL, RL>) => Stream<AL, ER | EL, RR | RL>; <AL, EL, RL, AR, ER, RR>(left: Stream<AL, EL, RL>, right: Stream<AR, ER, RR>): Stream<AL, EL | ER, RL | RR>; }

Source

Since v2.0.0