effect-io-ai

Package: effect
Module: Effect

Effect.mapErrorEager

Applies mapError eagerly when an effect is already resolved.

When to use

Use when an already-resolved failed effect should apply an error transformation immediately while pending effects still use regular error mapping.

Details

Success effects pass through unchanged because there is no error to transform. Failure effects apply the mapping function immediately, and pending effects fall back to regular mapError behavior.

Example (Mapping errors eagerly when possible)

import { Effect } from "effect"

// For resolved failure effects, the error mapping is applied immediately
const failed = Effect.fail("original error")
const mapped = Effect.mapErrorEager(failed, (err: string) => `mapped: ${err}`) // Applied eagerly

// For pending effects, behaves like regular mapError
const pending = Effect.delay(Effect.fail("error"), "100 millis")
const mappedPending = Effect.mapErrorEager(
  pending,
  (err: string) => `mapped: ${err}`
) // Uses regular mapError

Signature

declare const mapErrorEager: { <E, E2>(f: (e: E) => E2): <A, R>(self: Effect<A, E, R>) => Effect<A, E2, R>; <A, E, R, E2>(self: Effect<A, E, R>, f: (e: E) => E2): Effect<A, E2, R>; }

Source

Since v4.0.0