Type systems are generally formulated as collections of rules for checking the 'consistency' of programs. Type systems check that values are used appropriately according to their declared types throughout a program.

8. “Type systems are generally formulated as collections of rules
for checking the ‘consistency’ of programs.”
Benjamin C. Pierce

14. is, as?, as! (as )
$ swift
Welcome to Apple Swift version 2.2 (swiftlang-703.0.18.8
clang-703.0.30).
Type :help for assistance.
1> 1 is Any
$R0: Bool = true
2> 1 is AnyObject
$R1: Bool = false
3> import Foundation
4> 1 is Any
$R2: Bool = true
5> 1 is AnyObject
$R3: Bool = true // ???

15. is, as?, as! (as )
$ swift
Welcome to Apple Swift version 2.2 (swiftlang-703.0.18.8
clang-703.0.30).
Type :help for assistance.
1> [1] is [Any]
$R0: Bool = true
2> [1] is [AnyObject]
repl.swift:2:5: error: 'Bool' is not convertible to ‘[AnyObject]’ // ???
[1] is [AnyObject]
~~~~^~~~~~~~~~~~~~
2> import Foundation
3> [1] is [Any]
$R3: Bool = true
4> [1] is [AnyObject]
$R4: Bool = true

21.
nil
nil

24. $ ghci
GHCi, version 7.8.3: http://www.haskell.org/ghc/ :? for help
…
Prelude> let square x = x * x
Prelude> :info square
square :: Num a => a -> a
Prelude> square 10
100

25. expression statement
// Objective-C
NSMutableAttributedString *mutableAttributedString =
[[NSMutableAttributedString alloc] init];
// Swift
let mutableAttributedString = NSMutableAttributedString()

26. • 3: Int (default), IntXX, UIntXX,
Double, Float, …
• 3.14159: Double (default), Float, …

27. $ swift
Welcome to Apple Swift version 2.2 (swiftlang-703.0.18.8
clang-703.0.30).
Type :help for assistance.
1> let x1 = 3
x1: Int = 3 // inferred to be Int
2> let x2 = Double(3)
x2: Double = 3 // inferred to be Double
3> let x3: Double = 3
x3: Double = 3 // explicit type specified
4> let y1 = 3.14159
y1: Double = 3.1415899999999999 // inferred to be Double
5> let y2 = Float(3.14159)
y2: Float = 3.14159012 // inferred to be Float
6> let y3: Float = 3.14159
y3: Float = 3.14159012 // explicit type specified

28. import CoreGraphics
// func CGPointMake(_ x: CGFloat, _ y: CGFloat) -> CGPoint
let x = CGFloat(1.0 / 3) // 1 / 3 = 0(?), 1.0 / 3 = 0.333
let y = CGFloat(1.0 / 3) // 1.0 / 3: Double to CGFloat
let p = CGPointMake(x, y)
// CGFloat Swift
// “1 / 3” “CGFloat / CGFloat -> CGFloat”
// “1” “3” “CGFloat”
let p = CGPointMake(1 / 3, 1 / 3)