# 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.

## Signatures

```ts
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

```ts
import { Fx } from "@typed/fx"

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