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variable / @typed/fx

Fx.zipLeft

Zips two Fx streams in strict lockstep and emits only the left value. Completes when the first of the two streams completes.

Package version
2.0.0-beta.7
Category
Combining sources
Since
1.0.0
Member of
Fx

Follow one execution

Each fresh right value permits one left value; the right payload is discarded.

Fx timelinezipLeft(left, right)zipLeft
OperatorzipLeft(left, right)
Read this diagram

Follow each lane from left to right. Events stacked vertically share a tick; the green cursor marks the current time across every lane.

  • A value
    The text inside the pill is the emitted value.
  • Work starts
    The raised chevron starts an inner run (^ in the source).
  • The run returns
    The vertical bar ends this lane’s run.
  • A cause is delivered
    The exclamation mark belongs to this lane.
  • Work is interrupted
    The cross marks cancellation of this run.
  • Current time
    The line and diamond move together across all lanes.
  • Happening now
    A highlighted event is at the current tick.
  • Still ahead
    Muted, dashed values have not happened yet.
  • Time continues
    The lane’s arrow is not a return marker. An empty stretch can be quiet work that is still running.

Illustrated ticks start at 0. At 1×, one illustrated tick takes one second; captions specify real durations when timing matters. A cause or interruption belongs to its lane, and other work may continue. Scroll horizontally to inspect the rest of a long timeline.

Both sources run concurrently. The first run to complete ends pairing and interrupts the other, while consumer interruption stops both. A failure Cause is delivered to the Sink but does not by itself end pairing; a producer may continue and supply a value afterward.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

import { Fx } from "@typed/fx";

Access Fx.zipLeft through the imported Fx export. Its declaration below describes the member.

This public exposure is a re-export. Its import path is supported; declaration documentation is shared with the other public exposures below.

Signatures

export declare const zipLeft: {
    <A2, E2, R2>(that: Fx<A2, E2, R2>): <A, E, R>(self: Fx<A, E, R>) => Fx<A, E | E2, R | R2>;
    <A, E, R, A2, E2, R2>(self: Fx<A, E, R>, that: Fx<A2, E2, R2>): Fx<A, E | E2, R | R2>;
};

Why

zipLeft uses the right source as a one-for-one pacing or validation partner while retaining the left payload. It emits one left value per completed pair and preserves pair order.

Ownership and lifetime

Both sources run concurrently. The first run to complete ends pairing and interrupts the other, while consumer interruption stops both. A failure Cause is delivered to the Sink but does not by itself end pairing; a producer may continue and supply a value afterward.

Examples

import { Cause, Effect, Ref } from "effect"
import { Fx, Sink } from "@typed/fx"

const program = Effect.gen(function* () {
  const deliveries = yield* Ref.make<Array<string>>([])
  const left = Fx.make<number, string>((sink) =>
    sink.onFailure(Cause.fail("warning")).pipe(Effect.andThen(sink.onSuccess(1)))
  )
  yield* Fx.zipLeft(left, Fx.succeed("pair")).run(Sink.make(
    () => Ref.update(deliveries, (xs) => [...xs, "failure"]),
    (value) => Ref.update(deliveries, (xs) => [...xs, `value:${value}`])
  ))
  return yield* Ref.get(deliveries) // ["failure", "value:1"]
})

Other public imports

These import paths expose the same declaration. Each page retains its own public name and signature.

Source