func testAll() {
    // 'property' notation allows us to name our tests.  This becomes important
    // when they fail and SwiftCheck reports it in the console.
    property("Integer Equality is Reflexive") <- forAll { (i : Int) in
        return i == i
    }
}

property("The reverse of the reverse of an array is that array") <- forAll { (xs : [Int]) in
    // This property is using a number of SwiftCheck's more interesting 
    // features.  `^&&^` is the conjunction operator for properties that turns
    // both properties into a larger property that only holds when both sub-properties
    // hold.  `<?>` is the labelling operator allowing us to name each sub-part
    // in output generated by SwiftCheck.  For example, this property reports:
    //
    // *** Passed 100 tests
    // (100% , Right identity, Left identity)
    return
        (xs.reverse().reverse() == xs) <?> "Left identity"
        ^&&^
        (xs == xs.reverse().reverse()) <?> "Right identity"
}

property("Shrunken lists of integers always contain [] or [0]") <- forAll { (l : [Int]) in
    // Here we use the Implication Operator `==>` to define a precondition for
    // this test.  If the precondition fails the test is discarded.  If it holds
    // the test proceeds.
    return (!l.isEmpty && l != [0]) ==> {
        let ls = self.shrinkArbitrary(l)
        return (ls.filter({ $0 == [] || $0 == [0] }).count >= 1)
    }
}

property("Gen.one(of:) multiple generators picks only given generators") <- forAll { (n1 : Int, n2 : Int) in
    let g1 = Gen.pure(n1)
    let g2 = Gen.pure(n2)
    // Here we give `forAll` an explicit generator.  Before SwiftCheck was using
    // the types of variables involved in the property to create an implicit
    // Generator behind the scenes.
    return forAll(Gen.one(of: [g1, g2])) { $0 == n1 || $0 == n2 }
}

/// The Sieve of Eratosthenes:
///
/// To find all the prime numbers less than or equal to a given integer n:
///    - let l = [2...n]
///    - let p = 2
///    - for i in [(2 * p) through n by p] {
///          mark l[i]
///      }
///    - Remaining indices of unmarked numbers are primes
func sieve(_ n : Int) -> [Int] {
    if n <= 1 {
        return []
    }

    var marked : [Bool] = (0...n).map { _ in false }
    marked[0] = true
    marked[1] = true

    for p in 2..<n {
        for i in stride(from: 2 * p, to: n, by: p) {
            marked[i] = true
        }
    }

    var primes : [Int] = []
    for (t, i) in zip(marked, 0...n) {
        if !t {
            primes.append(i)
        }
    }
    return primes
}

/// Short and sweet check if a number is prime by enumerating from 2...⌈√(x)⌉ and checking 
/// for a nonzero modulus.
func isPrime(n : Int) -> Bool {
    if n == 0 || n == 1 {
        return false
    } else if n == 2 {
        return true
    }
    
    let max = Int(ceil(sqrt(Double(n))))
    for i in 2...max {
        if n % i == 0 {
            return false
        }
    }
    return true
}

import SwiftCheck

property("All Prime") <- forAll { (n : Int) in
    return sieve(n).filter(isPrime) == sieve(n)
}

import SwiftCheck
 
public struct ArbitraryFoo {
    let x : Int
    let y : Int

    public var description : String {
        return "Arbitrary Foo!"
    }
}

extension ArbitraryFoo : Arbitrary {
    public static var arbitrary : Gen<ArbitraryFoo> {
        return Gen<(Int, Int)>.zip(Int.arbitrary, Int.arbitrary).map(ArbitraryFoo.init)
    }
}

class SimpleSpec : XCTestCase {
    func testAll() {
        property("ArbitraryFoo Properties are Reflexive") <- forAll { (i : ArbitraryFoo) in
            return i.x == i.x && i.y == i.y
        }
    }
}

public static var arbitrary : Gen<MyClass> {
    return Gen<MyClass>.compose { c in
        return MyClass(
            // Use the nullary method to get an `arbitrary` value.
            a: c.generate(),

            // or pass a custom generator
            b: c.generate(Bool.suchThat { $0 == false }),

            // .. and so on, for as many values and types as you need.
            c: c.generate(), ...
        )
    }
}

public struct ArbitraryMutableFoo : Arbitrary {
    var a: Int8
    var b: Int16
    
    public init() {
        a = 0
        b = 0
    }
    
    public static var arbitrary: Gen<ArbitraryMutableFoo> {
        return Gen.compose { c in
            var foo = ArbitraryMutableFoo()
            foo.a = c.generate()
            foo.b = c.generate()
            return foo
        }
    }
}

let onlyEven = Int.arbitrary.suchThat { $0 % 2 == 0 }

let vowels = Gen.fromElements(of: [ "A", "E", "I", "O", "U" ])

let randomHexValue = Gen<UInt>.choose((0, 15))

let uppers = Gen<Character>.fromElements(in: "A"..."Z")
let lowers = Gen<Character>.fromElements(in: "a"..."z")
let numbers = Gen<Character>.fromElements(in: "0"..."9")
 
/// This generator will generate `.none` 1/4 of the time and an arbitrary
/// `.some` 3/4 of the time
let weightedOptionals = Gen<Int?>.frequency([
    (1, Gen<Int?>.pure(nil)),
    (3, Int.arbitrary.map(Optional.some))
])

.package(url: "https://github.com/typelift/SwiftCheck.git", from: "0.8.1")