FunctionalReadability.swift

/*
 Some playing around with a playground in Swift to try and figure out how to make Funcitonal
 stuff more readable. Initial example from:
 http://www.raywenderlich.com/82599/swift-functional-programming-tutorial
 */

import Foundation

let words = [ "Cat", "Chicken", "fish", "Dog", "Mouse", "Guinea Pig", "monkey"]

typealias Entry = (Character, [String])

//Example 1: Imperative

//func buildIndex(words: [String]) -> [Entry] {
//    var result = [Entry]()
//    
//    var letters = [Character]()
//    for word in words {
//        let firstLetter = Character(word.substringToIndex(advance(word.startIndex, 1)).uppercaseString)
//        
//        if !contains(letters, firstLetter) {
//            letters.append(firstLetter)
//        }
//    }
//    
//    for letter in letters {
//        var wordsForLetter = [String]()
//        for word in words {
//            let firstLetter = Character(word.substringToIndex(advance(word.startIndex, 1)).uppercaseString)
//            
//            if firstLetter == letter {
//                wordsForLetter.append(word)
//            }
//        }
//        
//        result.append((letter, wordsForLetter))
//    }
//    
//    return result
//}
//
//println(buildIndex(words))

//Helper functions

func distinct<T: Equatable>(source:[T]) -> [T] {
    var unique = [T]()
    
    for item in source {
        if !contains(unique, item) {
            unique.append(item)
        }
    }
    
    return unique
}

func firstLetter(str: String) -> Character {
    return Character(str.substringToIndex(advance(str.startIndex, 1)).uppercaseString)
}

//Example 2: Pure functional

func megaFunctionalIndex(words: [String]) -> [Entry] {
    return sorted(distinct(words.map(firstLetter))).map {
        (letter) -> Entry in
        return (letter, words.filter {
            (word) -> Bool in
            firstLetter(word) == letter
        })
    }
}

println("MEGA FUNCTIONAL!!!")
println(megaFunctionalIndex(words))

//Example 3: Somewhat easier to read functional

func buildIndex(words: [String]) -> [Entry] {
    func entryForLetter(letter: Character) -> Entry {
        func stringsForLetter(letter: Character) -> [String] {
            return words.filter {
                (word) -> Bool in
                firstLetter(word) == letter
            }
        }
        
        return (letter, stringsForLetter(letter))
    }
    
    let firstLetters = words.map(firstLetter)
    let distinctFirstLetters = distinct(firstLetters)
    let sortedFirstLetters = sorted(distinctFirstLetters, { $0 < $1 })

    return sortedFirstLetters.map(entryForLetter)
}

println("READABLE!!!")
println(buildIndex(words))