Search documentation

Search by topic, API name, or import path.

GitHub ↗

variable / @typed/fx

Fx.callback

Creates an Fx from a callback-based source.

Package version
2.0.0-beta.13
Category
Callback sources
Since
1.0.0
Member of
Fx

Follow one execution

Register lazily; external callbacks fork deliveries. Consumer cancellation closes the registration scope and runs its returned cleanup Effect.

Fx timelinecallback(register)callback
Operatorcallback(register)
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.

Registration is lazy: run is called once for each Fx run. The run creates a child scope and stays active until emit.done(), sink early exit, or interruption. If run returns an Effect, it is registered as the scope finalizer. Each emit operation starts its sink handler in a fiber, so handler completion can overlap; use the returned fibers or a serialized source when ordering of effects matters.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Access Fx.callback 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 callback: <A, E = never, R = never>(run: (emit: Emit<A, E>) => void | Effect.Effect<unknown, never, R>) => Fx<A, E, R>;

Why

DOM events, sockets, observers, and foreign libraries decide when values exist. callback turns that push boundary into Fx while keeping failure and cleanup inside Effect’s structured lifetime.

Ownership and lifetime

Registration is lazy: run is called once for each Fx run. The run creates a child scope and stays active until emit.done(), sink early exit, or interruption. If run returns an Effect, it is registered as the scope finalizer. Each emit operation starts its sink handler in a fiber, so handler completion can overlap; use the returned fibers or a serialized source when ordering of effects matters.

Examples

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

const messages = callback<string>((emit) => {
  const timer = setInterval(() => emit.succeed("tick"), 10)
  return Effect.sync(() => clearInterval(timer))
})
const program = collectUpTo(messages, 2)

Other public imports

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

Source