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variable / @typed/fx

Fx.if

Conditionally runs one of two Fx streams based on the boolean value emitted by the condition stream.

Package version
2.0.0-beta.7
Category
Conditional sources
Since
1.0.0
Member of
Fx

Follow one execution

Every condition value selects a branch and interrupts the prior active branch before forwarding replacement values.

Fx timelineif switches from the true branch to the false branchif
Operatorif(condition, { onTrue, onFalse })
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.

The required Scope owns the active branch. Replacement interrupts and awaits the previous branch; consumer interruption closes active work. Failures are delivered to the Sink.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Access Fx.if 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 { if_ as if };
declare const if_: {
    <B, E2, R2, C, E3, R3>(matchers: {
        onTrue: Fx<B, E2, R2>;
        onFalse: Fx<C, E3, R3>;
    }): <E, R>(condition: Fx<boolean, E, R>) => Fx<B | C, E | E2 | E3, R | R2 | R3 | Scope>;
    <E, R, B, E2, R2, C, E3, R3>(condition: Fx<boolean, E, R>, matchers: {
        onTrue: Fx<B, E2, R2>;
        onFalse: Fx<C, E3, R3>;
    }): Fx<B | C, E | E2 | E3, R | R2 | R3 | Scope>;
};

Why

if turns boolean pushes into a switchable branch. Each condition value selects one branch, interrupts the previous branch, and forwards only values from the currently selected Fx.

Ownership and lifetime

The required Scope owns the active branch. Replacement interrupts and awaits the previous branch; consumer interruption closes the active work. Failures are delivered to the Sink and only become terminal when the chosen Sink policy interrupts observation.

Examples

import { Fx } from "@typed/fx"
const status = Fx.if(Fx.fromIterable([true, false]), { onTrue: Fx.succeed("on"), onFalse: Fx.succeed("off") })

Other public imports

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

Source