Functional Programming in Kotlin - Android DroidJam India 2018 Rivu Chakraborty 

Rivu Chakraborty • A learner • Sr. Software Engineer (Android) @ Indus Net Technologies Pvt. Ltd. • Community Lead: GDG Kolkata, Kotlin Kolkata • Instructor @ Caster.io • Author – Reactive Programming in Kotlin • Author – Functional Kotlin • Author – Coroutines for Android Developers (WIP) • Author – Hands on Data Structures & Algorithms in Kotlin (WIP) @rivuchakraborty 

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What is Functional Programming? • Representation of Mathematical Function State Traditional / Imperative / Von Neuman Style Input Output 

Why Functional Programming • Modulation of code • FP encourages safe ways of programming through Immutability & Pure Functions • Testing becomes easier • Programs are easier to read. 

What are Functional Languages? • Any language that gives support to Functions as first class citizens are called Functional Language. 

Pure Functions • Same return value for same input, can be cached • Doesn’t modify anything outside function scope (No side effects) fun square(n:Int):Int { return n*n } 

Immutability • Immutability != Read Only • Kotlin doesn’t force Immutability, it encourages Immutability • The val keyword doesn’t guarantees immutability 

Lambda • To be generic, lambda or lambda expressions generally means anonymous functions, that is, functions without names, which can be assigned to variables, passed as arguments, or returned from another function fun invokeSomeStuff(doSomeStuff:()->Unit) { doSomeStuff() } fun main(args: Array) { invokeSomeStuff { println("doSomeStuff called"); } } 

Arrow • Functional companion to Kotlin’s Standard Library 

Type Constructors • Type Constructors are mainly theoretical concept. It’s not a Kotlin class constructor building a type. • We can reference Generic Parameterised Types as Type Constructors List Map Option Either 

Type Constructors • Option • Either • Try 

Type Classes • Type classes encode behaviour • You can use typeclasses as a DSL to access new free functionality for an existing type, or treat them as an abstraction placeholder for any one type that can implement the typeclass. The extension functions are scoped within the typeclass so they do not pollute the global namespace! • Example: Monads, Functors, Applicatives 

Monads, Functors, Applicatives 

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