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variable / @typed/fx

Fx.tap

Performs an effect for each element of the Fx, without changing the elements.

Package version
2.0.0-beta.13
Category
Transforming values
Since
1.0.0
Member of
Fx

Follow one execution

The observation Effect finishes before its original payload is forwarded. Concurrent producers can overlap callback Effects; these rows assume serial delivery.

Fx timelinetap(oneTurnCallback)tap
Operatortap(oneTurnCallback)
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.

Returned Effects run in the consumer path and are interrupted with it; a void callback is treated as Effect.void. Callback failures and services remain visible in the result type.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Access Fx.tap 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 tap: {
    <A, E2 = never, R2 = never>(f: (a: A) => void | Effect.Effect<unknown, E2, R2>): <E, R>(self: Fx<A, E | E2, R>) => Fx<A, E | E2, R | R2>;
    <A, E, R, E2 = never, R2 = never>(self: Fx<A, E | E2, R>, f: (a: A) => void | Effect.Effect<unknown, E2, R2>): Fx<A, E | E2, R | R2>;
};

Why

tap sequences an observation or side effect before forwarding each original value. It emits exactly once per successful callback, in source order; callback failure prevents that value.

Ownership and lifetime

Returned Effects run in the consumer path and are interrupted with it; a void callback is treated as Effect.void. Callback failures and services remain visible in the result type.

Examples

import { Effect } from "effect"
import { Fx } from "@typed/fx"
const logged = Fx.fromIterable([1, 2]).pipe(Fx.tap((n) => Effect.log(n)))

Other public imports

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

Source