Semigroup

Combine values systematically with the concat operation

What is Semigroup?

A Semigroup is a type that has a way to combine two values into one (called concat). It's associative, meaning the order of operations doesn't matter. Perfect for merging configurations, combining validation results, or aggregating data.

// Instead of manual merging:
const merged = { ...obj1, ...obj2 }

// Use Semigroup:
const merged = Semigroup.concat(obj1, obj2)
concat
struct
first/last
combining patterns
➕

Concat Operation

Combine two values into one

🔗

Associative

Order of operations doesn't matter

⚙️

Composable

Build complex combiners from simple ones

🌐

Universal

Works with any type of data

Semigroup in Action

❌ Manual Merging

const merge = (a: Settings, b: Settings): Settings => ({
  theme: b.theme || a.theme,
  language: b.language || a.language,
  notifications: b.notifications || a.notifications
})

// Repetitive, error-prone

✅ Semigroup Approach

const SettingsSemigroup = S.struct({
  theme: S.first<string>(),
  language: S.first<string>(),
  notifications: S.first<boolean>()
})

const merge = SettingsSemigroup.concat
// Declarative, reusable

Practice Exercises

1

Basic

Learn about basic in fp-ts semigroup

beginnerStart
2

Struct

Learn about struct in fp-ts semigroup

beginnerStart
3

First Last

Learn about first last in fp-ts semigroup

beginnerStart
4

Practical

Learn about practical in fp-ts semigroup

intermediateStart

Why Learn Semigroup?

🔗

Master Semigroup

Learn the fundamental concepts and patterns that make Semigroup powerful

💪

4 Exercises

Practice with hands-on exercises from intermediate level

🚀

Production Ready

Apply Semigroup patterns to build robust, type-safe applications