effect-io-ai

Package: effect
Module: Effect

Effect.retry

Retries a failing effect based on a defined retry policy.

Details

The Effect.retry function takes an effect and a Schedule policy, and will automatically retry the effect if it fails, following the rules of the policy.

If the effect ultimately succeeds, the result will be returned.

If the maximum retries are exhausted and the effect still fails, the failure is propagated.

When to Use

This can be useful when dealing with intermittent failures, such as network issues or temporary resource unavailability. By defining a retry policy, you can control the number of retries, the delay between them, and when to stop retrying.

Example (Retrying with a Fixed Delay)

import { Effect, Schedule } from "effect"

let count = 0

// Simulates an effect with possible failures
const task = Effect.async<string, Error>((resume) => {
  if (count <= 2) {
    count++
    console.log("failure")
    resume(Effect.fail(new Error()))
  } else {
    console.log("success")
    resume(Effect.succeed("yay!"))
  }
})

// Define a repetition policy using a fixed delay between retries
const policy = Schedule.fixed("100 millis")

const repeated = Effect.retry(task, policy)

Effect.runPromise(repeated).then(console.log)
// Output:
// failure
// failure
// failure
// success
// yay!

Example (Retrying a Task up to 5 times)

import { Effect } from "effect"

let count = 0

// Simulates an effect with possible failures
const task = Effect.async<string, Error>((resume) => {
  if (count <= 2) {
    count++
    console.log("failure")
    resume(Effect.fail(new Error()))
  } else {
    console.log("success")
    resume(Effect.succeed("yay!"))
  }
})

// Retry the task up to 5 times
Effect.runPromise(Effect.retry(task, { times: 5 })).then(console.log)
// Output:
// failure
// failure
// failure
// success

Example (Retrying Until a Specific Condition is Met)

import { Effect } from "effect"

let count = 0

// Define an effect that simulates varying error on each invocation
const action = Effect.failSync(() => {
  console.log(`Action called ${++count} time(s)`)
  return `Error ${count}`
})

// Retry the action until a specific condition is met
const program = Effect.retry(action, {
  until: (err) => err === "Error 3"
})

Effect.runPromiseExit(program).then(console.log)
// Output:
// Action called 1 time(s)
// Action called 2 time(s)
// Action called 3 time(s)
// {
//   _id: 'Exit',
//   _tag: 'Failure',
//   cause: { _id: 'Cause', _tag: 'Fail', failure: 'Error 3' }
// }

See

• retryOrElse for a version that allows you to run a fallback.
• repeat if your retry condition is based on successful outcomes rather than errors.

Signature

declare const retry: { <E, O extends NoExcessProperties<Retry.Options<E>, O>>(options: O): <A, R>(self: Effect<A, E, R>) => Retry.Return<R, E, A, O>; <B, E, R1>(policy: Schedule.Schedule<B, NoInfer<E>, R1>): <A, R>(self: Effect<A, E, R>) => Effect<A, E, R1 | R>; <A, E, R, O extends NoExcessProperties<Retry.Options<E>, O>>(self: Effect<A, E, R>, options: O): Retry.Return<R, E, A, O>; <A, E, R, B, R1>(self: Effect<A, E, R>, policy: Schedule.Schedule<B, NoInfer<E>, R1>): Effect<A, E, R1 | R>; }

Source

Since v2.0.0