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variable / @typed/fx

Fx.catch

Recovers from the first typed failure of an Fx by running a fallback Fx.

Package version
2.0.0-beta.13
Category
Errors and recovery
Since
1.0.0
Member of
Fx

Follow one execution

Alias of catch_; the diagram uses this export name.

Fx timelinecatch_(fallback)catch
Operatorcatch (alias of catch_)
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.

See catch_ for the shared behavior and lifetime contract.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

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

Access Fx.catch 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 { catch_ as catch };
export declare const catch_: {
    <E, A2, E2, R2>(f: (e: E) => Fx<A2, E2, R2>): <A, R>(self: Fx<A, E, R>) => Fx<A | A2, E2, R | R2>;
    <A, E, R, A2, E2, R2>(self: Fx<A, E, R>, f: (e: E) => Fx<A2, E2, R2>): Fx<A | A2, E2, R | R2>;
};

Why

Typed failures are part of an Fx’s public error channel, so callers often need to replace a failed producer based on its first typed failure. This is the push-stream counterpart of Effect’s typed recovery.

Ownership and lifetime

The source runs until it reports a Cause containing a Fail. The first typed failure starts exactly one fallback and the entire original Cause is replaced, including any defects or interrupts composed beside that Fail. A Cause with no Fail passes through unchanged. Source values already delivered remain delivered. The fallback’s services become requirements of the returned Fx, and external interruption stops whichever run is active.

Examples

import { catch as recover } from "@typed/fx/Fx"
import { fail, succeed } from "@typed/fx/Fx"

const resilient = recover(fail("offline"), (error) => succeed(error.length))
Recovering a Fail discards its complete composite Cause
```ts
import { Cause } from "effect"
import { catch as recover } from "@typed/fx/Fx"
import { failCause, succeed } from "@typed/fx/Fx"

const composite = Cause.combine(Cause.fail("offline"), Cause.die("socket defect"))
const recovered = recover(failCause(composite), () => succeed("cached"))
```

Other public imports

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

Source