Search documentation

Search by topic, API name, or import path.

GitHub ↗

variable / @typed/fx/Fx

loop

Loops over an Fx with an accumulator, producing a new value for each element and updating the accumulator.

Package version
2.0.0-beta.7
Category
Stateful transforms
Since
1.0.0

Follow one execution

Loops over an Fx with an accumulator, producing a new value for each element and updating the accumulator.

Fx timelineloop separates its private state from its one output per eventloop
Operatorloop(position, label)
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.

A fresh accumulator starts from seed for each run and is discarded when that run ends. The pure callback adds no failures, services, fibers, or resources.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Signatures

export declare const loop: {
    <B, A, C>(seed: B, f: (acc: B, a: A) => readonly [
        C,
        B
    ]): <E, R>(self: Fx<A, E, R>) => Fx<C, E, R>;
    <A, E, R, B, C>(self: Fx<A, E, R>, seed: B, f: (acc: B, a: A) => readonly [
        C,
        B
    ]): Fx<C, E, R>;
};

Why

loop is the primitive for a synchronous state machine over pushed values. Every input emits exactly one output and installs exactly one next state, preserving source order.

Ownership and lifetime

A fresh accumulator starts from seed for each run and is discarded when that run ends. The pure callback adds no failures, services, fibers, or resources.

Examples

import { Fx } from "@typed/fx"

const indexed = Fx.fromIterable(["a", "b"]).pipe(Fx.loop(0, (index, value) => [[index, value] as const, index + 1]))

Other public imports

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

Source