WHAT IS FUNCTIONAL PROGRAMMING?

A Programming paradigm

• Functions as values
• Declarative
• Pure Functions
• No Shared State
• No Mutating Data
• No Side-Effects

WHY FUNCTIONAL PROGRAMMING?

functional code becomes

• More predictable
• Safer
• More Modular
• More Testable
• Less Verbose

WHY FUNCTIONAL PROGRAMMING IN JAVASCRIPT?

BECAUSE WE CAN!

QUICK ES6 FEATURE REVIEW

CONST, LET

arrow functions

FUNCTIONAL SOFTWARE CONSTRUCTION

THE MOST IMPORTANT concept

HOW DO WE COMPOSE?

class-based composition has limits

function-based composition IS more expressive

HIGher-level abstractions

Functional programming is not strictly superior to object oriented programming

HELLO RAMDA.JS

Familiar...

DATA-LAST

flexible calls

functional programming principles

functions are values

Declarative vs imperative

Pure Functions & referential transparency

Immutable operations

Map, reduce, filter

Higher-order functions

Currying functions

Pointfree Style

Compose, Pipe

DRAWBACKS TO FP IN JS

hard to read

• Good Variable Naming
• Use a Type System (Typescript or Flow)
• Break up large anonymous compositions

harder to debug

• Insert transparent helpers for debugging

Less Efficient

• Don't prematurely optimize
• If performance matters, refactor

NEXT STEPS

Ramda Adjunct

https://github.com/char0n/ramda-adjunct

Ramda extension library

Fantasy Land

https://github.com/fantasyland/fantasy-land​

Specification for "algebraic Data Structures" in JS

Type Systems

https://github.com/Microsoft/TypeScript​

improve safety of functional programs

https://github.com/facebook/flow​

Functional Compile-to-JS Languages

• ReasonML

• Purescript

• Elm

Other Pure Functional Languages

• Haskell

• OCAML

• F# (.NET)

• Scala, Clojure (JVM)

• Erlang

• Scheme, LISP

FUNCTIONAL PROGRAMMING & LAMBDA CALCULUS

"Lambda" Function

monads

monoids

functors

chain

applicatives

bind

apply

setoids

CASE STUDY: DATA TRANSFORMATION PIPELINES