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variable / @typed/fx/Fx

dropUntilEffect

Drops elements from an Fx until an effectful predicate returns true. Emits from the first element for which the predicate effect succeeds with true (including that element) and all following elements.

Package version
2.0.0-beta.13
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 predicate still runs after the gate opens.

Fx timelinedropUntilEffect(oneTurnCheck)dropUntilEffect
OperatordropUntilEffect(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.

The gate is per run. Predicate effects inherit producer ordering and concurrency, are interrupted with their invoking delivery, and expose E2/R2. Failures remain observable after the gate opens.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Signatures

export declare const dropUntilEffect: {
    <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

dropUntilEffect makes the gate decision Effectful. The first true opens the gate and is forwarded, but its skipWhileEffect implementation eagerly evaluates the predicate for every later value as well; those later boolean results no longer affect forwarding.

Ownership and lifetime

The gate is per run. Predicate effects inherit producer ordering and concurrency, are interrupted with their invoking delivery, and expose E2/R2. Failures remain observable after the gate opens.

Examples

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

const program = Effect.gen(function* () {
  const checks = yield* Ref.make(0)
  const values = yield* Fx.collectAll(
    Fx.fromIterable([2, 3]).pipe(
      Fx.dropUntilEffect((n) => Ref.update(checks, (count) => count + 1).pipe(Effect.as(n === 2)))
    )
  )
  return { values, checks: yield* Ref.get(checks) } // { values: [2, 3], checks: 2 }
})

Other public imports

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

Source