Follow one execution
Register lazily; external callbacks fork deliveries. Consumer cancellation closes the registration scope and runs its returned cleanup Effect.
callbackTick 0. External: register; Consumer: start; Listener: start.
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.
Import
import { callback } from "@typed/fx/Fx";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.