Functional Programming demo

recursion.clj

(defn rtake
  [n lst]
  (if (= n 0)
    ()
    (cons (first lst)
          (rtake (dec n) (rest lst)))))

(def my-first (partial rtake 1))

(defn rzip
  [a b]
  (if (or (empty? a) (empty? b))
    ()
    (cons (list (first a) (first b))
          (rzip (rest a) (rest b)))))

(defn rmax
  ([lst] (rmax lst -10000))
  ([lst biggest]
   (if (empty? lst)
     biggest
     (let [cur (first lst)]
       (rmax (rest lst)
             (if (> cur biggest)
               cur
               biggest))))))

swifty.swift

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

import UIKit

func makeIncrementer() -> (Int -> Int) {
    var x: Int = 0
    return { (step: Int) -> Int in
        x += step
        return x
    }
}
// x = 8 // Error!
let inc1 = makeIncrementer()
inc1(1)
inc1(1)
inc1(3)
let inc2 = makeIncrementer()
inc2(1)
inc1(1)
inc2(1)

let names = ["Adam", "John", "Jason", "James"]
// impertative
var totalNameLength = 0
for name in names {
    if name.hasPrefix("J") {
        totalNameLength += name.lengthOfBytesUsingEncoding(NSUTF8StringEncoding)
    }
}
totalNameLength

// functional with higher-order functions
let lengths = names.filter({ name in name.hasPrefix("J")}
    ).map({ name in name.lengthOfBytesUsingEncoding(NSUTF8StringEncoding) }
    ).reduce(0, combine: { total, nameLength in total + nameLength})
lengths