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.