IO/IOEither

Synchronous side effects with type safety

What is IO/IOEither?

IO represents a synchronous side effect that you can control. Like Task but for sync operations. Defer file I/O, console logging, or any side effect until you're ready to execute it. Perfect for testing and controlling when effects happen.

// Effect runs immediately:
fs.writeFileSync('data.txt', data)

// IO defers the effect:
const write = IO.of(() => fs.writeFileSync(...))
write() // runs when you want
lazy computation
tryCatch
chain
fromIO
config loading
⏱️

Lazy Side Effects

Defer execution until needed

🔄

Synchronous

No async complexity

🧪

Testable

Control when effects execute

✅

Type-Safe

IOEither for error handling

IO/IOEither in Action

❌ Direct Side Effects

function saveToFile(data: string) {
  fs.writeFileSync('data.txt', data)
  console.log('Saved!')
}

// Executes immediately
// Hard to test

✅ IO Approach

const saveToFile = (data: string): IO<void> =>
  () => {
    fs.writeFileSync('data.txt', data)
    console.log('Saved!')
  }

// Lazy, testable
saveToFile(data)() // Execute when ready

Practice Exercises

1

Basic Io

Learn about basic io in fp-ts io

beginnerStart
2

Io Chain

Learn about io chain in fp-ts io

beginnerStart
3

Ioeither Basic

Learn about ioeither basic in fp-ts io

beginnerStart
4

Trycatch

Learn about trycatch in fp-ts io

intermediateStart
5

Chain

Learn about chain in fp-ts io

intermediateStart
6

From Io

Learn about from io in fp-ts io

intermediateStart
7

Practical

Learn about practical in fp-ts io

advancedStart

Why Learn IO/IOEither?

💾

Master IO/IOEither

Learn the fundamental concepts and patterns that make IO/IOEither powerful

💪

7 Exercises

Practice with hands-on exercises from advanced level

🚀

Production Ready

Apply IO/IOEither patterns to build robust, type-safe applications