effect-io-ai

Package: effect
Module: Effect

Effect.catchTag

Catches and handles specific errors by their _tag field, which is used as a discriminator.

When to Use

catchTag is useful when your errors are tagged with a readonly _tag field that identifies the error type. You can use this function to handle specific error types by matching the _tag value. This allows for precise error handling, ensuring that only specific errors are caught and handled.

The error type must have a readonly _tag field to use catchTag. This field is used to identify and match errors.

Example (Handling Errors by Tag)

import { Effect, Random } from "effect"

class HttpError {
  readonly _tag = "HttpError"
}

class ValidationError {
  readonly _tag = "ValidationError"
}

//      ┌─── Effect<string, HttpError | ValidationError, never>
//      ▼
const program = Effect.gen(function* () {
  const n1 = yield* Random.next
  const n2 = yield* Random.next
  if (n1 < 0.5) {
    yield* Effect.fail(new HttpError())
  }
  if (n2 < 0.5) {
    yield* Effect.fail(new ValidationError())
  }
  return "some result"
})

//      ┌─── Effect<string, ValidationError, never>
//      ▼
const recovered = program.pipe(
  // Only handle HttpError errors
  Effect.catchTag("HttpError", (_HttpError) =>
    Effect.succeed("Recovering from HttpError")
  )
)

See

• catchTags for a version that allows you to handle multiple error types at once.

Signature

declare const catchTag: { <E, const K extends RA.NonEmptyReadonlyArray<E extends { _tag: string; } ? E["_tag"] : never>, A1, E1, R1>(...args: [...tags: K, f: (e: Extract<NoInfer<E>, { _tag: K[number]; }>) => Effect<A1, E1, R1>]): <A, R>(self: Effect<A, E, R>) => Effect<A | A1, Exclude<E, { _tag: K[number]; }> | E1, R | R1>; <A, E, R, const K extends RA.NonEmptyReadonlyArray<E extends { _tag: string; } ? E["_tag"] : never>, A1, E1, R1>(self: Effect<A, E, R>, ...args: [...tags: K, f: (e: Extract<NoInfer<E>, { _tag: K[number]; }>) => Effect<A1, E1, R1>]): Effect<A | A1, Exclude<E, { _tag: K[number]; }> | E1, R | R1>; }

Source

Since v2.0.0