Forking: Renamed Combinators and New Options

The fork* family of combinators has been renamed in v4 for clarity, and all variants now accept an options object for controlling fiber startup behavior.

Renamings

v3	v4	Description
Effect.fork	Effect.forkChild	Fork as a child of the current fiber
Effect.forkDaemon	Effect.forkDetach	Fork detached from parent lifecycle
Effect.forkScoped	Effect.forkScoped	Fork tied to the current Scope (unchanged)
Effect.forkIn	Effect.forkIn	Fork in a specific Scope (unchanged)
Effect.forkAll	—	Removed
Effect.forkWithErrorHandler	—	Removed

Effect.fork → Effect.forkChild

v3

import { Effect } from "effect"

const fiber = Effect.fork(myEffect)

v4

import { Effect } from "effect"

const fiber = Effect.forkChild(myEffect)

Effect.forkDaemon → Effect.forkDetach

v3

import { Effect } from "effect"

const fiber = Effect.forkDaemon(myEffect)

v4

import { Effect } from "effect"

const fiber = Effect.forkDetach(myEffect)

Fork Options

In v4, forkChild, forkDetach, forkScoped, and forkIn all accept an optional options object with the following fields:

{
  readonly startImmediately?: boolean | undefined
  readonly uninterruptible?: boolean | "inherit" | undefined
}

• startImmediately — When true, the forked fiber begins executing immediately rather than being deferred. Defaults to undefined (deferred).
• uninterruptible — Controls whether the forked fiber can be interrupted. true makes it uninterruptible, "inherit" inherits the parent’s interruptibility, and undefined uses the default behavior.

Usage as data-last (curried)

import { Effect } from "effect"

const fiber = myEffect.pipe(
  Effect.forkChild({ startImmediately: true })
)

Usage as data-first

import { Effect } from "effect"

const fiber = Effect.forkChild(myEffect, { startImmediately: true })

Removed Combinators

Effect.forkAll and Effect.forkWithErrorHandler have been removed in v4. For forkAll, fork effects individually with forkChild or use higher-level concurrency combinators. For error handling on forked fibers, observe the fiber’s result via Fiber.join or Fiber.await.