Intro to functional programming

functional.swift

//: Playground - noun: a place where people can play

import UIKit

func makeIncr() -> (Int -> Int) {
    var x = 0
    return { y in x += y; return x }
}

let inc1 = makeIncr()
inc1(1)
inc1(1)
inc1(2)
let inc2 = makeIncr()
inc2(1)
inc1(1)
inc2(3)

func maxTail(lst: [Int], biggest: Int = Int.min) -> Int {
    if lst.count == 0 { return biggest }
    let next = lst.first!
    let nextBiggest = next > biggest ? next : biggest
    return maxTail(Array(lst[1..<lst.count]), biggest: nextBiggest)
}

func max(lst: [Int]) -> Int {
    // base case
    if lst.count == 0 { return Int.min }
    // recursive
    let head = lst.first!
    let restMax = max(Array(lst[1..<lst.count]))
    return head > restMax ? head : restMax
}

max([1,2,3,4,5])
max([5,4,3,2,1])
max([10, 100, -7, 99, 8])

func take(n: Int, list: Array<Int>) -> Array<Int> {
    if n == 0 { return [] } // base case
    // recursive case
    return [list.first!] + take(n - 1, Array(list[1..<list.count]))
}

take(3, [1,2,3,4,5])
take(1, [1,3,4,5,6])
take(0, [1,2])

let data = [1,2,3,4,5]
let foo = data.map({ x in x + 1 }).filter({ $0 % 2 == 0}).reduce(0, combine: +)

var bar = 0
for x in data {
    let y = x + 1
    if y % 2 == 0 {
        bar += y
    }
}

let words = ["foo", "bar", "baz", "foobar"]
let totalLength = words.reduce(0, combine: { (count: Int, word: String) -> Int in
    count + word.lengthOfBytesUsingEncoding(0)
})
totalLength

let keys = ["foo", "bar", "baz"]
let vals = [1,2,3]
let dict = Array(zip(keys, vals)).map({ z in (z.0 + "-key", z.1) }).reduce([:], combine: { (dict: [String:Int], tuple: (String,Int)) -> [String:Int] in
    var d = dict; d[tuple.0] = tuple.1; return d } )
dict