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changesWithEffect

Drops consecutive elements that are considered equal by an effectful predicate. When the effect returns true, the element is skipped; when false, it is emitted.

This is the effectful variant of skipRepeatsWith: instead of a pure Equivalence<A>, you supply (prev, next) => Effect<boolean> where true means “equal” (skip) and false means “changed” (emit).

Package version
2.0.0-beta.7
Category
Selecting values
Since
1.0.0

Follow one execution

Drops consecutive elements that are considered equal by an effectful predicate. When the effect returns true, the element is skipped; when false, it is emitted. This is the effectful variant of skipRepeatsWith: instead of a pure Equivalence<A>, you supply (prev, next) => Effect<boolean> where true means “equal” (skip) and false means “changed” (emit).

Fx timelinechangesWithEffect waits for each equivalence check before deciding the next outputchangesWithEffect
OperatorchangesWithEffect(sameStatus)
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.

One previous value and a semaphore are scoped to each run. Comparison effects are serialized, interrupted with the run, and add their failures and services to the resulting Fx.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Signatures

export declare const changesWithEffect: {
    <A, E2, R2>(f: (prev: A, next: A) => Effect.Effect<boolean, E2, R2>): <E, R>(fx: Fx<A, E | E2, R>) => Fx<A, E | E2, R | R2>;
    <A, E, R, E2, R2>(fx: Fx<A, E | E2, R>, f: (prev: A, next: A) => Effect.Effect<boolean, E2, R2>): Fx<A, E | E2, R | R2>;
};

Why

changesWithEffect supports service-backed or failing equivalence checks. The first value always emits; every later value is compared with the last emitted value and emits only when the effect returns false, preserving source order.

Ownership and lifetime

One previous value and a semaphore are scoped to each run. Comparison effects are serialized, interrupted with the run, and add their failures and services to the resulting Fx.

Examples

import { Effect } from "effect"
import { Fx } from "@typed/fx"

const changes = Fx.fromIterable([1, 1, 2]).pipe(
  Fx.changesWithEffect((previous, next) => Effect.succeed(previous === next)),
)

Other public imports

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

Source