functional programming

fp.swift

// Functional Programming exercises.
//
// Rules:
//   1. No loops (for, while, do/while)!
//   2. No if, else, or switch statements.
//   3. No "var" variables - only "let".
//
// Functions to use:
// map, reduce, filter
//
// String functions that might be helpful:
//   contains("Some String", "g") --> returns true if "Some String" contains the character "g"
//   "Some String".hasSuffix("foo") --> returns true if "Some String" ends with "foo"

// Create some test data for our purposes
struct Person {
    let name: String
    let emailAddresses: [String]
}

let john = Person(name: "John Smith", emailAddresses: ["jsmith@gmail.com", "john@smith.org"])
let bob = Person(name: "Bob Jones", emailAddresses: ["bob@jones.org"])
let fred = Person(name: "Fred Barnes", emailAddresses: ["fbarnes@gmail.com", "fred@yahoo.com", "barnes@work.com"])

let people = [john, bob, fred]

// ---------------------------------------------------------------------------------------------

// Exercise 1: Create a list of the peoples' names.
let names: [String] = people.map { return $0.name}

// Upon completion of exercise 1, this should evaluate to "true".
names == ["John Smith", "Bob Jones", "Fred Barnes"]

// ---------------------------------------------------------------------------------------------

// Exercise 2: Create a "flattened" list containing all email addresses of all people.
// NOTE: This should be a [String], not a [ [String] ].

let emailAddressArray: [[String]] = people.map { return $0.emailAddresses }
let emails: [String] = emailAddressArray.reduce([]){
    return $0 + $1
}// YOU FILL THIS IN

// Upon completion of exercise 2, this should evaluate to "true".
let expectEmails = ["jsmith@gmail.com", "john@smith.org",
                    "bob@jones.org",
                    "fbarnes@gmail.com", "fred@yahoo.com", "barnes@work.com"]
emails == expectEmails

// ---------------------------------------------------------------------------------------------

// Exercise 3: Create a list of all people who have the letter "J" somewhere in their name.
let peopleWithJ: [Person] = people.filter {
    return contains($0.name, "J")
}// YOU FILL THIS IN

// Upon completion of exercise 3, these should evaluate to "true".
peopleWithJ.count == 2
peopleWithJ[0].name == "John Smith"
peopleWithJ[1].name == "Bob Jones"

// ---------------------------------------------------------------------------------------------

// Silver Challenge: Create a list of all people who have an @gmail.com email address.
let expectGmailPeople = [john, fred]
let gmailPeople: [Person] = expectGmailPeople.filter {
    return countElements($0.emailAddresses.filter {
        return $0.hasSuffix("@gmail.com")
    }) > 0
}// YOU FILL THIS IN
gmailPeople.count == 2
gmailPeople[0].name == "John Smith"
gmailPeople[1].name == "Fred Barnes"

// ---------------------------------------------------------------------------------------------

// Gold Challenge: Solve Exercise 2 again, this time without using reduce.
// Hint: Look up the "join" function.
let emailStrings: [String] = people.map {
    join(",", $0.emailAddresses)
}
let emailStrings2: String = join(",", emailStrings)
let goldChallengeEmails: [String] = split(emailStrings2, {$0 == ","}, maxSplit: Int.max, allowEmptySlices: false)
goldChallengeEmails == expectEmails