Summary - Functional programming

Combine immutability, Sequence and Result to write a functional pipeline.

Summary - Functional programming

In this group you saw the core of functional programming: immutability with data class, pure functions, laziness with Sequence, accumulation with fold and the monad approach with Result.

This lesson includes a small task that combines three of them: you will define a data class and compute a total with fold. This pattern is the foundation of functional Kotlin.

Exercise Summary: Product and fold

Define a data class Product(val name: String, val price: Int). In main create a list of three products, compute the total price with fold(0) { acc, p -> acc + p.price } and print it with println.

Show example solution

data class Product(val name: String, val price: Int)

fun main() {
    val items = listOf(
        Product("Bread", 20),
        Product("Milk", 15),
        Product("Tea", 25)
    )
    val total = items.fold(0) { acc, p -> acc + p.price }
    println(total)
}

Test yourself

Which is a core feature of functional programming?
- Immutable data
- Lots of side effects
- Frequent global state mutation
- Loops everywhere
Show answer

Immutable data — Immutability is core to functional programming.
Match the FP concepts

data class

Immutability
fun double(n)

Pure function
asSequence()

Laziness
fold(0)

Accumulation

Complete the fold call

val total = items.____(0) { acc, item -> acc + item.price }

Show answer

val total = items.fold(0) { acc, item -> acc + item.price }

Next lesson: windowed

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies