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Fx.pairwise

Emits consecutive pairs [previous, current]. The first value is not emitted until a second value arrives.

Equivalent to RxJS pairwise and Effect Stream.sliding(2) for pairs.

Package version
2.0.0-beta.7
Category
Stateful transforms
Since
1.0.0
Member of
Fx

Follow one execution

Emits consecutive pairs [previous, current]. The first value is not emitted until a second value arrives. Equivalent to RxJS pairwise and Effect Stream.sliding(2) for pairs.

Fx timelinepairwise waits for a prior value, then emits adjacent transitionspairwise
Operatorpairwise
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.

The previous-value cell belongs to one run of the returned Fx and is discarded when that run completes or is interrupted. Source errors and services are unchanged.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Access Fx.pairwise 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 pairwise: <A, E = never, R = never>(self: Fx<A, E, R>) => Fx<readonly [
    A,
    A
], E, R>;

Why

pairwise exposes transitions rather than isolated values. For n inputs it emits max(0, n - 1) adjacent pairs in source order, retaining only the immediately preceding value.

Ownership and lifetime

The previous-value cell belongs to one run of the returned Fx and is discarded when that run completes or is interrupted. Source errors and services are unchanged.

Examples

import { Fx } from "@typed/fx"

const changes = Fx.fromIterable([10, 13, 12]).pipe(Fx.pairwise)

Other public imports

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

Source