the cats toolbox a quick tour of some basic typeclasses

The Cats toolbox: a quick tour of some basic typeclasses

Pawel Szulc

@rabbitonweb

What’s a type class?

What’s a type class?trait Semigroup[A] { def combine(x: A, y: A): A}

What’s a type class?trait Semigroup[A] { def combine(x: A, y: A): A}

def merge[A](a1: A, a2: A)(implicit ev: Semigroup[A]) = ev.combine(a1, a2)

What’s a type class?trait Semigroup[A] { def combine(x: A, y: A): A}

final class SemigroupOps[A](a: A)(implicit ev: Semigroup[A]) { def |+|(other: A): A = ev.combine(a, other) def combine(rhs: A): A = ev.combine(a, other)}

def merge[A](a1: A, a2: A)(implicit ev: Semigroup[A]) = ev.combine(a1, a2)

What’s a type class?trait Semigroup[A] { def combine(x: A, y: A): A}

final class SemigroupOps[A](a: A)(implicit ev: Semigroup[A]) { def |+|(other: A): A = ev.combine(a, other) def combine(rhs: A): A = ev.combine(a, other)}

def merge[A](a1: A, a2: A)(implicit ev: Semigroup[A]) = a1 combine a2

What’s a type class?trait Semigroup[A] { def combine(x: A, y: A): A}

final class SemigroupOps[A](a: A)(implicit ev: Semigroup[A]) { def |+|(other: A): A = ev.combine(a, other) def combine(rhs: A): A = ev.combine(a, other)}

def merge[A](a1: A, a2: A)(implicit ev: Semigroup[A]) = a1 |+| a2

What’s a type class?trait Semigroup[A] { def combine(x: A, y: A): A}

final class SemigroupOps[A](a: A)(implicit ev: Semigroup[A]) { def |+|(other: A): A = ev.combine(a, other) def combine(rhs: A): A = ev.combine(a, other)}

def merge[A : Semigroup](a1: A, a2: A) = a1 |+| a2

So academic

So academic

So pointlessly detached from real-world problems

So academic

So pointlessly detached from real-world problemsDo they have

real-world applications

Looking for Jobin Londonwith Cats

Apples & Oranges

Apples & OrangesStep 1

➔ You are building a checkout system for a shop

which only sells apples and oranges.

➔ Apples cost 60p and oranges cost 25p.

➔ Build a checkout system which takes a list of

items scanned at the till and outputs the total

cost

➔ For example: [ Apple, Apple, Orange, Apple]

=> £2.05

Lets implement it!https://github.com/rabbitonweb/cats_toolbox

Apples & OrangesStep 1

➔ You are building a checkout system for a shop

which only sells apples and oranges.

➔ Apples cost 60p and oranges cost 25p.

➔ Build a checkout system which takes a list of

items scanned at the till and outputs the total

cost

➔ For example: [ Apple, Apple, Orange, Apple]

=> £2.05

Apples & OrangesStep 1

➔ You are building a checkout system for a shop

which only sells apples and oranges.

➔ Apples cost 60p and oranges cost 25p.

➔ Build a checkout system which takes a list of

items scanned at the till and outputs the total

cost

➔ For example: [ Apple, Apple, Orange, Apple]

=> £2.05

Step 2

➔ The shop decides to introduce two new

offers

◆ buy one, get one free on Apples

◆ 3 for the price of 2 on Oranges

➔ Update your checkout functions accordingly

Thank you :)@rabbitonweb

paul.szulc@gmail.com