scheduling-hello-world.mdx

title	Your First Schedule
id	scheduling-hello-world
skillLevel	beginner
applicationPatternId	scheduling
summary	Learn the basics of scheduling in Effect - retry operations and repeat them on intervals.
tags	scheduling retry repeat getting-started
rule	description Use Schedule to control when and how often effects run.
author	PaulJPhilp
related	scheduling-repeat-interval scheduling-exponential-backoff
lessonOrder	2

Guideline

Use Schedule to control timing in Effect programs - retrying failed operations, repeating successful ones, or adding delays.

---

Rationale

Schedules solve common timing problems:

1. Retries - Try again after failures
2. Polling - Check for updates periodically
3. Rate limiting - Control how fast things run
4. Backoff - Increase delays between attempts

---

Good Example

import { Effect, Schedule } from "effect"

// ============================================
// 1. Retry a failing operation
// ============================================

let attempts = 0
const flakyOperation = Effect.gen(function* () {
  attempts++
  if (attempts < 3) {
    yield* Effect.log(`Attempt ${attempts} failed`)
    return yield* Effect.fail(new Error("Temporary failure"))
  }
  return `Success on attempt ${attempts}`
})

// Retry up to 5 times
const withRetry = flakyOperation.pipe(
  Effect.retry(Schedule.recurs(5))
)

// ============================================
// 2. Repeat a successful operation
// ============================================

const logTime = Effect.gen(function* () {
  const now = new Date().toISOString()
  yield* Effect.log(`Current time: ${now}`)
  return now
})

// Repeat 3 times
const repeated = logTime.pipe(
  Effect.repeat(Schedule.recurs(3))
)

// ============================================
// 3. Add delays between operations
// ============================================

// Repeat every second, 5 times
const polling = logTime.pipe(
  Effect.repeat(
    Schedule.spaced("1 second").pipe(
      Schedule.intersect(Schedule.recurs(5))
    )
  )
)

// ============================================
// 4. Common schedule patterns
// ============================================

// Fixed delay between attempts
const fixedDelay = Schedule.spaced("500 millis")

// Increasing delay (1s, 2s, 4s, 8s...)
const exponentialBackoff = Schedule.exponential("1 second")

// Maximum number of attempts
const limitedAttempts = Schedule.recurs(3)

// Combine: exponential backoff, max 5 attempts
const retryPolicy = Schedule.exponential("100 millis").pipe(
  Schedule.intersect(Schedule.recurs(5))
)

// ============================================
// 5. Run examples
// ============================================

const program = Effect.gen(function* () {
  yield* Effect.log("--- Retry Example ---")
  const result = yield* withRetry
  yield* Effect.log(`Result: ${result}`)

  yield* Effect.log("\n--- Repeat Example ---")
  yield* repeated
})

Effect.runPromise(program)

Common Schedules

Schedule	What It Does
Schedule.recurs(n)	Run at most n times
Schedule.spaced(duration)	Wait duration between runs
Schedule.exponential(base)	Double the delay each time
Schedule.forever	Run indefinitely
Schedule.once	Run exactly once

Combining Schedules

Combinator	Meaning
intersect	Both conditions must be true
union	Either condition can be true
andThen	First schedule, then second

When to Use

• Retries - Network requests, database connections
• Polling - Check for job completion
• Rate limiting - API call quotas
• Periodic tasks - Health checks, cache refresh