As you know, in the , section , it is said that Pragmatic Programmer Your Knowledge Portfolio Learn at least one new language every year. Different languages solve the same problems in different ways. By learning several different approaches, you can help broaden your thinking and avoid getting stuck in a rut. Additionally, learning many languages is far easier now, thanks to the wealth of freely available software on the Internet I see learning programming languages as a chance to open up my horizon and learn some new concepts. It also encourage good habit like immutability, composition, modulation, … I’d like to review some of the features of all the languages I have played with. Some are useful, some just make me interested or say “wow” Curly braces Each language can have its own style of grouping block of code, but I myself like the curly braces the most, which are cute :] Some like C, Java, Swift, … use curly braces **Swift** init(total: Double, taxPct: Double) { self.total = total self.taxPct = taxPct subtotal = total / (taxPct + 1)} Some like Haskell, Python, … use indentation **Haskell** bmiTell :: (RealFloat a) => a -> String bmiTell bmi | bmi <= 18.5 = "You're underweight, you emo, you!" | bmi <= 25.0 = "You're supposedly normal. Pffft, I bet you're ugly!" | bmi <= 30.0 = "You're fat! Lose some weight, fatty!" | otherwise = "You're a whale, congratulations!" Some like Elixir use keyword list **ELixir** if false, do: :this, else: :that Named parameter Language like Objective C, Swift offer named parameter, which make it easier to reason about a function call func sayHello(to person: String, and anotherPerson: String) -> String { return "Hello \(person) and \(anotherPerson)!"} Explicit type Language like C, Swift, Java, … have type information in parameter and in return, which make it easier to reason about a function call **Swift** func sayHello(personName: String, alreadyGreeted: Bool) -> String { if alreadyGreeted { return sayHelloAgain(personName) } else { return sayHello(personName) }} List comprehension Languages like Haskell, Python, Elixir, support list comprehension **Elixir** iex> for n <- [1, 2, 3, 4], do: n * n[1, 4, 9, 16] First class function I enjoy functional programming, so first class function support in Javascript, Swift, Haskell, Elixir, … really make me happy **Haskell** zipWith' (*) (replicate 5 2) [1..] Curry Currying is the technique of translating the evaluation of a function that takes multiple arguments (or a tuple of arguments) into evaluating a sequence of functions, each with a single argument (partial application) Language like Swift 2, Haskell, … have curry by default. Some like Javascript can use libraries (Lodash, …) to achieve this. In Haskell, every function officially only takes one parameter. In Swift 3, curry was :( removed Haskell multThree :: (Num a) => a -> a -> a -> a multThree x y z = x * y * z By calling functions with too few parameters, we’re creating new functions on the fly. **Javascript** var curry = require('lodash.curry');var map = curry(function(f, ary) { return ary.map(f);});var getChildren = function(x) { return x.childNodes;};

var allTheChildren = map(getChildren); Pattern matching I find pattern matching as a better way around statement if else Swift supports pattern matching in statement switch **Swift** enum Trades { case Buy(stock: String, amount: Int, stockPrice: Float) case Sell(stock: String, amount: Int, stockPrice: Float)}

let aTrade = Trades.Buy(stock: "APPL", amount: 200, stockPrice: 115.5)

switch aTrade {case .Buy(let stock, let amount, _): process(stock, amount)case .Sell(let stock, let amount, _): process(stock, amount * -1)} Some like Haskell, Elixir, … also pattern matches on function name, which makes it work great for recursion **Haskell** sayMe :: (Integral a) => a -> String sayMe 1 = "One!" sayMe 2 = "Two!" sayMe 3 = "Three!" sayMe 4 = "Four!" sayMe 5 = "Five!" sayMe x = "Not between 1 and 5" 

map _ [] = []map f (x:xs) = f x : map f xs In Elixir, the operator is actually a match operator = **Elixir** iex> x = 11iex> x1iex> 1 = x1iex> 2 = x** (MatchError) no match of right hand side value: 1 Recursion Some language like Haskell, Elixir, … don’t use loop, they use recursion with performance in mind, no overflow. Haskell length' :: (Num b) => [a] -> b length' [] = 0 length' (_:xs) = 1 + length' xs Laziness Some languages support infinite collection, thanks to their laziness. Haskell is lazy, if you map something over a list several times and filter it several times, it will only pass over the list once **Haskell** largestDivisible :: (Integral a) => a largestDivisible = head (filter p [100000,99999..]) where p x = x `mod` 3829 == 0 Elixir defines the concept of with and with Eager Enum Lazy Stream **Elixir** 1..100_000 |> Enum.map(&(&1 * 3)) |> Enum.filter(odd?) |> Enum.sum Custom operator Elixir is famous for its operator pipe |> The |> symbol used in the snippet above is the pipe operator: it simply takes the output from the expression on its left side and passes it as the first argument to the function call on its right side Elixir 1..100_000 |> Enum.map(&(&1 * 3)) |> Enum.filter(odd?) |> Enum.sum Haskell often takes advantage of this custom operator -: Haskell x -: f = f x 

(0,0) -: landLeft 1 -: landRight 1 -: landLeft 2 Functor, Applicative Functor, Monoid, Monad I really like enjoy Haskell because of these typeclasses. It realizes common pattern (map, apply, join, bind, …) with comptutational context. It really enlightens me when I find that is a Monad as well (you should read the ) function Reader monad **Haskell** instance Monad Maybe where return x = Just x Nothing >>= f = Nothing Just x >>= f = f x fail _ = Nothing 

landLeft :: Birds -> Pole -> Maybe Pole landLeft n (left,right) | abs ((left + n) - right) < 4 = Just (left + n, right) | otherwise = Nothing 

landRight :: Birds -> Pole -> Maybe Pole landRight n (left,right) | abs (left - (right + n)) < 4 = Just (left, right + n) | otherwise = Nothing

ghci> return (0,0) >>= landLeft 1 >>= banana >>= landRight 1 Nothing List comprehension in Haskell is just syntactic sugar for using lis as Monad **Haskell** ghci> [ (n,ch) | n <- [1,2], ch <- ['a','b'] ] [(1,'a'),(1,'b'),(2,'a'),(2,'b')] **Swift** enum Result<T> { case Value(T) case Error(NSError)}

extension Result { func map(f: T -> U) -> Result { switch self { case let .Value(value): return Result.Value(f(value)) case let .Error(error): return Result.Error(error) } }}

extension Result { static func flatten<T>(result: Result<Result<T>>) -> Result<T> { switch result { case let .Value(innerResult): return innerResult case let .Error(error): return Result<T>.Error(error) } }}

extension Result { func flatMap(f: T -> Result) -> Result { return Result.flatten(map(f)) }} Trait and mixin Languages like Scala, … support trait Similar to interfaces in Java, traits are used to define object types by specifying the signature of the supported methods. Unlike Java, Scala allows traits to be partially implemented; i.e. it is possible to define default implementations for some methods **Scala** trait Similarity { def isSimilar(x: Any): Boolean def isNotSimilar(x: Any): Boolean = !isSimilar(x)}

class Point(xc: Int, yc: Int) extends Similarity { var x: Int = xc var y: Int = yc def isSimilar(obj: Any) = obj.isInstanceOf[Point] && obj.asInstanceOf[Point].x == x} Swift can uses to Protocol Extension achieve trait **Swift** protocol GunTrait { func shoot() -> String { return "Shoot" }}

protocol RenderTrait { func render() -> String { return "Render" }}

struct Player: GameObject, AITrait, GunTrait, RenderTrait, HealthTrait {

} Ruby supports via Mixin Module **Ruby** module Greetings def hello puts "Hello!" end

 def bonjour puts "Bonjour!" end

 def hola puts "Hola!" endend

class User include Greetingsend Delegate property There are certain common kinds of properties that would be very nice to implement once and for all like lazy, observable and storing. An example is in Kotlin class Delegate {operator fun getValue(thisRef: Any?, property: KProperty<*>): String {return "$thisRef, thank you for delegating '${property.name}' to me!"} operator fun setValue(thisRef: Any?, property: KProperty<\*>, value: String) { 
 println("$value has been assigned to '${property.name}' in $thisRef.") 
} } Where to go from here Hope you find something interesting. Each language has its own pros and is designed for specific purpose. So no list will be enough to cover them all. To take a quick peek into other programming languages, I find by Derek very helpful. Learn in One Video There are things that intrigue us every day like Swift initialization rule make it explicit when using initializer, Go goroutine and channel for concurrent code, Elixir process for easy concurrent and message communication. You’ll be amazed by how process encapsulates state, Haskell data type encourages immutability and thread safe code, Elixir macro for great extension of the language. The best way to to learn is to use and dive into the languages often. May your code continue to compile. While you are here, you may like my other posts Next to first, next to nothing 20 recommended utility apps for macOS in 2018 How to make tag selection view in React Native 8 ways to communicate between Fragment and Activity in Android apps

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