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variable / @typed/fx/Fx

takeWhileEffect

Takes elements from an Fx while an effectful predicate returns true. Stops at the first element for which the predicate effect succeeds with false; that element is not included.

Package version
2.0.0-beta.7
Category
Selecting values
Since
1.0.0

Follow one execution

Each predicate Effect takes one turn in this serialized source. Its failure is forwarded rather than treated as false. The boundary input is excluded and the source stops.

Fx timelinetakeWhileEffect(oneTurnCheck)takeWhileEffect
OperatortakeWhileEffect(oneTurnCheck)
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.

Predicate effects expose their failures and services and are interrupted with the run. A false result stops upstream; no independent fiber or buffer is retained.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Signatures

export declare const takeWhileEffect: {
    <A, E2, R2>(predicate: (a: A) => Effect.Effect<boolean, E2, R2>): <E, R>(fx: Fx<A, E, R>) => Fx<A, E | E2, R | R2>;
    <A, E, R, E2, R2>(fx: Fx<A, E, R>, predicate: (a: A) => Effect.Effect<boolean, E2, R2>): Fx<A, E | E2, R | R2>;
};

Why

takeWhileEffect performs the prefix decision with Effect and completes before the first false value, retaining source order.

Ownership and lifetime

Predicate effects expose their failures and services and are interrupted with the run. A false result stops upstream; no independent fiber or buffer is retained.

Examples

import { Effect } from "effect"
import { Fx } from "@typed/fx"
const small = Fx.fromIterable([1, 2]).pipe(Fx.takeWhileEffect((n) => Effect.succeed(n < 2)))

Other public imports

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

Source