effect-io-ai

Package: effect
Module: Layer

Layer.catchCause

Recovers from any failure cause by switching to another layer.

When to use

Use when you need Layer recovery to inspect more than the typed error, such as defects or interruption information.

Details

The handler receives the full Cause of the failed layer, including typed errors, unexpected defects, and interruption information, and returns the fallback layer to build instead. Finalizers for resources acquired by the failed layer are still run before the fallback layer is acquired.

Example (Recovering from layer failures by cause)

import { Context, Data, Effect, Layer } from "effect"

class DatabaseError extends Data.TaggedError("DatabaseError")<{
  message: string
}> {}

class Database extends Context.Service<Database, {
  readonly query: (sql: string) => Effect.Effect<string>
}>()("Database") {}

const primaryDatabaseLayer = Layer.effect(Database,
  Effect.fail(new DatabaseError({ message: "Primary DB unreachable" }))
)

const databaseWithFallback = primaryDatabaseLayer.pipe(
  Layer.catchCause(() => {
    return Layer.succeed(Database, {
      query: Effect.fn("Database.query")((sql: string) => Effect.succeed(`Memory: ${sql}`))
    })
  })
)

const program = Effect.gen(function*() {
  const database = yield* Database
  const result = yield* database.query("SELECT * FROM users")
  console.log(result)
}).pipe(
  Effect.provide(databaseWithFallback)
)

Effect.runPromise(program)
// Memory: SELECT * FROM users

See

• catchTag for recovering from specific tagged errors

Signature

declare const catchCause: { <E, RIn2, E2, ROut2>(onError: (cause: Cause.Cause<E>) => Layer<ROut2, E2, RIn2>): <RIn, ROut>(self: Layer<ROut, E, RIn>) => Layer<ROut & ROut2, E2, RIn2 | RIn>; <RIn, E, ROut, RIn2, E2, ROut22>(self: Layer<ROut, E, RIn>, onError: (cause: Cause.Cause<E>) => Layer<ROut22, E2, RIn2>): Layer<ROut & ROut22, E2, RIn | RIn2>; }

Source

Since v4.0.0