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variable / @typed/fx/Fx

filterMapLoopEffect

Effectfully loops over an Fx with an accumulator, producing an optional new value.

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

Follow one execution

Effectfully loops over an Fx with an accumulator, producing an optional new value.

Fx timelinefilterMapLoopEffect makes each zero-or-one decision after its Effect resolvesfilterMapLoopEffect
OperatorfilterMapLoopEffect(0, oneTurnEveryOther)
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.

One mutable seed belongs to each run. Callback Causes are delivered to the Sink, services remain required, and interruption follows each delivery; callers need a serialized producer for atomic state.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Signatures

export declare const filterMapLoopEffect: {
    <B, A, E2, R2, C>(seed: B, f: (acc: B, a: A) => Effect.Effect<readonly [
        Option.Option<C>,
        B
    ], E2, R2>): <E, R>(self: Fx<A, E | E2, R>) => Fx<C, E | E2, R | R2>;
    <A, E, R, B, R2, C>(self: Fx<A, E, R>, seed: B, f: (acc: B, a: A) => Effect.Effect<readonly [
        Option.Option<C>,
        B
    ], E, R2>): Fx<C, E, R | R2>;
};

Why

filterMapLoopEffect makes the state transition Effectful while retaining zero-or-one output per input. It adds no serialization: overlapping producer callbacks can read the same seed, complete out of order, and overwrite one another’s next state.

Ownership and lifetime

One mutable seed belongs to each run. Callback Causes are delivered to the Sink, services remain required, and interruption follows each delivery; callers need a serialized producer for atomic state.

Examples

import { Effect, Option } from "effect"
import { Fx } from "@typed/fx"

const counted = Fx.fromIterable(["a", "b"]).pipe(
  Fx.filterMapLoopEffect(0, (count, value) => Effect.succeed([Option.some(`${count}:${value}`), count + 1])),
)

Other public imports

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

Source