List of Listings

Chapter 1. Introduction to typing

Listing 1.1. Trying to interpret data as code

Listing 1.2. Insufficient type information

Listing 1.3. Refined type information

Listing 1.4. Bad mutation

Listing 1.5. Immutability

Listing 1.6. Not enough encapsulation

Listing 1.7. Encapsulation

Listing 1.8. Noncomposable system

Listing 1.9. Noncomposable system update

Listing 1.10. Composable system

Listing 1.11. Untyped find()

Listing 1.12. Typed find()

Listing 1.13. Dynamic typing

Listing 1.14. Static typing

Listing 1.15. Weak typing

Listing 1.16. Strong typing

Listing 1.17. Type inference

Chapter 2. Basic types

Listing 2.1. Raising and logging an error if a config file is not found

Listing 2.2. Empty type implemented as an uninstantiable class

Listing 2.3. A “Hello world!” function

Listing 2.4. Unit type implemented as a singleton without state

Listing 2.5. Gatekeeper

Listing 2.6. Alternative gatekeeper implementation

Listing 2.7. Function adding up item total

Listing 2.8. Checking for addition overflow

Listing 2.9. Currency class and currency addition function

Listing 2.10. Floating-point equality within epsilon

Listing 2.11. Simple text-breaking function

Listing 2.12. Text-breaking function using grapheme-splitter library

Listing 2.13. Linked-list implementation

Listing 2.14. Array-based list implementation

Listing 2.15. Array-based list implementation with additional capacity

Listing 2.16. Array-based binary tree implementation

Listing 2.17. Compact binary tree implementation

Chapter 3. Composition

Listing 3.1. Distance between two points

Listing 3.2. Distance between two points defined as tuples

Listing 3.3. Pair type

Listing 3.4. Distance between two points defined as records

Listing 3.5. Ill-formed currency

Listing 3.6. Currency maintaining invariants

Listing 3.7. Immutable Currency

Listing 3.8. Encoding day of week as a number

Listing 3.9. Encoding day of week with constants

Listing 3.10. Encoding day of week as an enum

Listing 3.11. Parsing input into a DayOfWeek or undefined

Listing 3.12. Optional type

Listing 3.13. Returning result and error from a function

Listing 3.14. Either type

Listing 3.15. Returning result or error from a function

Listing 3.16. Tagged union of shapes

Listing 3.17. Variant type

Listing 3.18. Union of shapes as variant

Listing 3.19. Naïve implementation

Listing 3.20. Processing with the visitor pattern

Listing 3.21. Variant visitor

Listing 3.22. Alternative processing with variant visitor

Chapter 4. Type safety

Listing 4.1. Sketch of incompatible components

Listing 4.2. Pound-force second and Newton-second types

Listing 4.3. Converting lbfs to Ns

Listing 4.4. Updated components

Listing 4.5. Constructor throwing on invalid value

Listing 4.6. Constructor coercing an invalid value

Listing 4.7. Factory returning undefined on invalid value

Listing 4.8. Type cast causing a run-time error

Listing 4.9. Revisiting Either implementation

Listing 4.10. makeLeft and makeRight

Listing 4.11. Triangle or Square

Listing 4.12. isLeft() and getLeft()

Listing 4.13. Upcast

Listing 4.14. Downcast

Listing 4.15. A collection of types implementing IDocumentItem

Listing 4.16. A collection of types as a sum type

Listing 4.17. A collection of unknown type

Listing 4.18. Serializing a cat

Listing 4.19. Deserializing a Cat

Listing 4.20. Serializing and tracking type

Listing 4.21. Deserializing with tracked type

Chapter 5. Function types

Listing 5.1. Car-wash strategy

Listing 5.2. Car-wash strategy revisited

Listing 5.3. Pluggable Greeter

Listing 5.4. helloWorld.ts

Listing 5.5. Chapter1.md

Listing 5.6. State machine implementation

Listing 5.7. Alternative state machine implementation

Listing 5.8. Eager Car production

Listing 5.9. Lazy Car production

Listing 5.10. Anonymous Car production

Listing 5.11. Ad hoc mapping

Listing 5.12. map()

Listing 5.13. Using map()

Listing 5.14. Ad hoc filtering

Listing 5.15. filter()

Listing 5.16. Using filter()

Listing 5.17. Ad hoc reducing

Listing 5.18. reduce()

Listing 5.19. Using reduce()

Chapter 6. Advanced applications of function types

Listing 6.1. WidgetFactory decorator

Listing 6.2. Functional widget factory

Listing 6.3. Functional widget factory decorator

Listing 6.4. Decorator function

Listing 6.5. Global counter

Listing 6.6. Object-oriented counter

Listing 6.7. Functional counter

Listing 6.8. Resumable counter

Listing 6.9. Synchronous execution

Listing 6.10. Asynchronous execution with callback

Listing 6.11. Counting down in an event loop

Listing 6.12. Two counters in an event loop

Listing 6.13. Counter with callback

Listing 6.14. Chaining callbacks

Listing 6.15. Functions returning promises

Listing 6.16. Chaining promises

Listing 6.17. getUserName() returning a promise

Listing 6.18. Rejecting a promise

Listing 6.19. Chaining functions returning promises

Listing 6.20. Chaining functions that don’t return promises

Listing 6.21. Using Promise.all() to sequence execution

Listing 6.22. Using Promise.race() to sequence execution

Listing 6.23. Chaining promises review

Listing 6.24. Using async/await

Chapter 7. Subtyping

Listing 7.1. Pound-force second and Newton-second types

Listing 7.2. Pound-force second and Newton-second without unique symbols

Listing 7.3. User is structurally a subtype of Named

Listing 7.4. Simulating nominal subtyping

Listing 7.5. Deserializing any

Listing 7.6. Run-time type checking for User

Listing 7.7. Stronger typing using unknown

Listing 7.8. TurnDirection to angle conversion

Listing 7.9. Error reporting

Listing 7.10. turnAngle() using fail()

Listing 7.11. turnAgain() using fail() and returning a dummy value

Listing 7.12. turnAngle() using fail() and returning its result

Listing 7.13. Triangle | Square as Triangle | Square | Circle

Listing 7.14. Triangle | Square | Circle as Triangle | Square

Listing 7.15. EquilateralTriangle declaration

Listing 7.16. Triangle[] as Shape[]

Listing 7.17. LinkedList<Triangle> as LinkedList<Shape>

Listing 7.18. () => Triangle as () => Shape

Listing 7.19. () => Shape as () => Triangle

Listing 7.20. Overriding a method with a subtype as return type

Listing 7.21. Draw and render functions

Listing 7.22. Shape and Triangle with isRightAngled() method

Listing 7.23. Updated draw and render functions

Listing 7.24. Attempting to call isRightAngled() on a supertype of Triangle

Chapter 8. Elements of object-oriented programming

Listing 8.1. Abstract logger

Listing 8.2. Logger interface

Listing 8.3. Extended logger interface

Listing 8.4. Combining interfaces

Listing 8.5. Bad inheritance

Listing 8.6. Expression hierarchy

Listing 8.7. Inheritance and composition

Listing 8.8. Ask the CEO

Listing 8.9. Geometry library

Listing 8.10. CircleAdapter

Listing 8.11. Hunting behavior

Listing 8.12. Extending an instance with the members of another one

Listing 8.13. Mixing in behavior

Listing 8.14. Visitor with OOP

Listing 8.15. Visitor with Variant

Listing 8.16. Functional expressions

Chapter 9. Generic data structures

Listing 9.1. getNumbers()

Listing 9.2. Default transform()

Listing 9.3. assembleWidgets()

Listing 9.4. Default pluck()

Listing 9.5. doNothing() and pluckAll()

Listing 9.6. Naïve identity

Listing 9.7. Unsafe use of any

Listing 9.8. Generic identity

Listing 9.9. Type safety

Listing 9.10. Optional type

Listing 9.11. Binary tree of numbers

Listing 9.12. Linked list of strings

Listing 9.13. Generic binary tree

Listing 9.14. Generic linked list

Listing 9.15. Print in order

Listing 9.16. printInOrder() example

Listing 9.17. Print linked list

Listing 9.18. printLinkedList() example

Listing 9.19. Iterator result

Listing 9.20. Iterator interface

Listing 9.21. Binary tree iterator

Listing 9.22. Linked list iterator

Listing 9.23. print() using iterator

Listing 9.24. contains() using iterator

Listing 9.25. Iterable interface

Listing 9.26. Iterable linked list

Listing 9.27. print() and contains() with Iterator argument

Listing 9.28. print() and contains() with Iterable argument

Listing 9.29. Binary tree iterator

Listing 9.30. Binary tree iterator using generator

Listing 9.31. Linked list iterator

Listing 9.32. Linked list iterator using generator

Listing 9.33. Iterable linked list using generator

Listing 9.34. Inifinite stream of random numbers

Listing 9.35. Consuming values from the stream

Listing 9.36. square()

Listing 9.37. take()

Listing 9.38. Pipeline

Chapter 10. Generic algorithms and iterators

Listing 10.1. map()

Listing 10.2. map() with iterator

Listing 10.3. filter()

Listing 10.4. filter() with iterator

Listing 10.5. reduce()

Listing 10.6. reduce() with iterator

Listing 10.7. filter()/reduce() pipeline

Listing 10.8. filter/reduce pipeline

Listing 10.9. Fluent iterable

Listing 10.10. Fluent filter/reduce pipeline

Listing 10.11. Better fluent iterable

Listing 10.12. Better fluent filter/reduce pipeline

Listing 10.13. renderAll sketch

Listing 10.14. renderAll with constraint

Listing 10.15. IComparable interface

Listing 10.16. max() algorithm

Listing 10.17. max() algorithm with compare() argument

Listing 10.18. reverse() with stack

Listing 10.19. reverse() for array

Listing 10.20. IReadable<T> and IIncrementable<T>

Listing 10.21. IInputIterator<T>

Listing 10.22. Linked list implementation

Listing 10.23. Linked list input iterator

Listing 10.24. Pair of iterators over linked list

Listing 10.25. IWritable<T> and IOutputIterator<T>

Listing 10.26. Console output iterator

Listing 10.27. map() with input and output iterators

Listing 10.28. find() with iterable

Listing 10.29. IForwardIterator<T>

Listing 10.30. LinkedListIterator<T> implementing IForwardIterator<T>

Listing 10.31. find() with forward iterator

Listing 10.32. Replacing 42 with 0 in a linked list

Listing 10.33. IBidirectionalIterator<T> and ArrayIterator<T>

Listing 10.34. reverse() with bidirectional iterator

Listing 10.35. Reversing an array of numbers

Listing 10.36. IRandomAccessIterator<T>

Listing 10.37. ArrayIterator<T> implementing a random-access iterator

Listing 10.38. Element at

Listing 10.39. elementAt() with input and random-access iterators

Listing 10.40. Adaptive elementAt()

Chapter 11. Higher kinded types and beyond

Listing 11.1. Generic map()

Listing 11.2. Optional type

Listing 11.3. Optional map()

Listing 11.4. Sum type map()

Listing 11.5. Box type

Listing 11.6. Box map()

Listing 11.7. square() and stringify()

Listing 11.8. readNumber() return type

Listing 11.9. Processing a number

Listing 11.10. Processing with map()

Listing 11.11. Processing with lambda

Listing 11.12. Unpacking values for square()

Listing 11.13. Unpacking values for stringify()

Listing 11.14. Using map()

Listing 11.15. Sketch of Functor interface

Listing 11.16. Box implementing the interface

Listing 11.17. Functor interface

Listing 11.18. Function map()

Listing 11.19. Applying map() over a function

Listing 11.20. Functions returning result or error

Listing 11.21. Either type

Listing 11.22. Processing and explicitly checking for errors

Listing 11.23. Either map()

Listing 11.24. Incompatible types

Listing 11.25. Either bind()

Listing 11.26. Branchless readCatFromFile()

Listing 11.27. map() on Box

Listing 11.28. bind() on Box

Listing 11.29. Box monad

Listing 11.30. Optional monad

Listing 11.31. Chaining promises

Listing 11.32. Divisors

Listing 11.33. All divisors

Listing 11.34. All anagrams

Listing 11.35. List bind()