Functional Programming Made Easier¶

Modules¶

Chapter Checklist¶

Introduction
Learning Functional Programming is Hard.
Learning Programming is Learning How to Think
Learning Functional Programming is Learning to Think Differently
Why Functional Programming?
You Cannot Describe an Experience
Barrier to Entry
Costs of Ownership
Case Study: Javascript
Case Study: Elm
Finding Developers
Finding Jobs
Who is This Book For?
From A to Z
A, B, X, Y, Z
A, B, C
X, Y, Z
A to Z
Why PureScript?
What’s PureScript?
Why not Haskell or Elm or ...?
Haskell
Elm
Some Other Functional Language
Why PureScript?
Four Part Harmony
Beginner
Intermediate
Advanced
Beyond
Exercises
So Many Pages
I: Beginner
- 1. Discipline is Freedom
  - 1.1. Global State
  - 1.2. Mutable State
    - 1.2.1. No Variables
    - 1.2.2. No Loops
  - 1.3. Purity
  - 1.4. Optimization
    - 1.4.1. Memoization
    - 1.4.2. Compiler Optimization
  - 1.5. Types
    - 1.5.1. Signal to Noise
    - 1.5.2. Perceived Limits
    - 1.5.3. Cake and Eat It
    - 1.5.4. Cutting Through the Noise
    - 1.5.5. Static Type Costs and Benefits
  - 1.6. Summary
- 2. The Power of Functions
  - 2.1. Functions as Parameters
  - 2.2. Functions as Return Values
  - 2.3. Higher-order Functions
  - 2.4. Composition
    - 2.4.1. Point-free Notation
  - 2.5. Currying
    - 2.5.1. Partial Application
- 3. The Basics of PureScript
  - 3.1. Types
    - 3.1.1. Javascript Primitives
Boolean Type
Char Type
String Type
Number Type - [ ] 3.1.2. PureScript Primitives
Int Type
Array Type
Record Type
Syntactical Oddity - [ ] 3.1.3. User Types
Type Alias
Data Type
Algebraic Data Types (ADTs)
New Types - [ ] 3.1.4. Common Library Types
Void
Unit
Maybe
Either
Maybe vs Either
Tuple
Either vs Tuple
List - [ ] 3.2. Pattern Matching - [ ] 3.2.1. Case Expression - [ ] 3.2.2. String Patterns - [ ] 3.2.3. Array Patterns - [ ] 3.2.4. List Patterns - [ ] 3.2.5. Array vs List - [ ] 3.2.6. Record Patterns - [ ] 3.3. Logical Control - [ ] 3.3.1. If-Then-Else Expression - [ ] 3.3.2. Case Expression - [ ] 3.3.3. Pattern Matching - [ ] 3.3.4. Guards - [ ] 3.4. Lambda Functions - [ ] 3.5. Wildcards - [ ] 3.5.1. Case Expression - [ ] 3.5.2. Operator Sections - [ ] 3.5.3. Records - [ ] 3.6. Bindings - [ ] 3.6.1. Where - [ ] 3.6.2. Let - [ ] 3.7. Binary Operators - [ ] 3.7.1. Associativity - [ ] 3.7.2. Precedence - [ ] 3.7.3. Fixity - [ ] 3.8. Comments - [ ] 3.9. Inferring Functionality from Type Signatures - [ ] 3.10. Summary
- 4. Installing PureScript
  - 4.1. Compiler and Tools
    - 4.1.1. Installing Node
For Node Already Installed
For Node NOT Installed - [ ] 4.1.2. Create Project
Initialize Project for npm and npx
Future-proofing
Install purescript and spago into your Project
Initialize Project for git (Optional) - [ ] 4.1.3. Initialize PureScript Project - [ ] 4.1.4. A Second Project - [ ] 4.2. Editor and Plugins - [ ] 4.2.1. Install Extensions - [ ] 4.2.2. Configure Extensions - [ ] 4.2.3. Configure Editor
- 5. Basic Coding in PureScript
  - 5.1. Prelude
  - 5.2. Exercise Program
  - 5.3. Pursuit
  - 5.4. Writing flip
    - 5.4.1. Hint for flip
    - 5.4.2. Code for flip
    - 5.4.3. Alternative Coding for flip
  - 5.5. Writing const
    - 5.5.1. Hint for const
    - 5.5.2. Code for const
  - 5.6. The Apply Operator ($)
  - 5.7. Writing apply
    - 5.7.1. Hint for ($)
    - 5.7.2. Code for ($)
  - 5.8. Writing the Apply Flipped Operator (#)
    - 5.8.1. Code for applyFlipped and (#)
  - 5.9. Preparing to Write Data.List Functions
  - 5.10. Why Data.List and not Data.Array
  - 5.11. Writing singleton
    - 5.11.1. Code for singleton
  - 5.12. Writing null
    - 5.12.1. Code for null
  - 5.13. Writing snoc
    - 5.13.1. Hint for snoc
    - 5.13.2. Code for snoc
  - 5.14. Writing length
    - 5.14.1. Hint for length
    - 5.14.2. Code for length
  - 5.15. Tail Recursion
    - 5.15.1. Observations regarding Tail Recursion
  - 5.16. Writing head
    - 5.16.1. Hint for head
    - 5.16.2. Code for head
  - 5.17. Writing tail
    - 5.17.1. Hint for tail
    - 5.17.2. Code for tail
  - 5.18. Writing last
    - 5.18.1. Hint for last
    - 5.18.2. Code for last
  - 5.19. Writing init
    - 5.19.1. Hint for init
    - 5.19.2. Code for init
  - 5.20. Writing uncons
    - 5.20.1. Code for uncons
  - 5.21. Writing index
    - 5.21.1. Hint for index
    - 5.21.2. Code for index
  - 5.22. Writing !!
    - 5.22.1. Hint for !!
    - 5.22.2. Code for !!
  - 5.23. Writing findIndex
    - 5.23.1. Hint for findIndex
    - 5.23.2. Code for findIndex
  - 5.24. Writing findLastIndex
    - 5.24.1. Hint for findLastIndex
    - 5.24.2. Code for findLastIndex
  - 5.25. Local Function Type Signatures
  - 5.26. Writing reverse
    - 5.26.1. Hints for reverse
    - 5.26.2. Code for reverse
  - 5.27. Writing concat
    - 5.27.1. Hint for concat
    - 5.27.2. Code for concat
  - 5.28. Writing filter
    - 5.28.1. Code for filter
    - 5.28.2. Alternative Coding for filter
  - 5.29. Tail Recursive version of filter
  - 5.30. Time vs Space
  - 5.31. Writing catMaybes
    - 5.31.1. Hint for catMaybes
    - 5.31.2. Code for catMaybes
  - 5.32. Writing range
    - 5.32.1. Hint for range
    - 5.32.2. Code for range
  - 5.33. Optimizing range
  - 5.34. Writing take
    - 5.34.1. Hint for take
    - 5.34.2. Code for take
  - 5.35. Writing drop
    - 5.35.1. Code for drop
  - 5.36. Writing takeWhile
    - 5.36.1. Code for takeWhile
  - 5.37. Writing dropWhile
    - 5.37.1. Code for dropWhile
  - 5.38. Writing takeEnd
    - 5.38.1. Hint for takeEnd
  - 5.39. Another Hint for takeEnd
    - 5.39.1. Code for takeEnd
  - 5.40. Writing dropEnd
    - 5.40.1. Code for dropEnd
  - 5.41. Writing zip
    - 5.41.1. Code for zip
  - 5.42. Writing unzip
    - 5.42.1. Code for unzip
II: Intermediate
- 6. Typeclasses
  - 6.1. The Problem
  - 6.2. The Solution
  - 6.3. Constraints
  - 6.4. Typeclass Requirement
  - 6.5. Built-in Typeclasses
    - 6.5.1. Eq Typeclass
    - 6.5.2. Ord Typeclass
    - 6.5.3. Show Typeclass
  - 6.6. Derived Instances
  - 6.7. Newtype Typeclass
  - 6.8. Deriving Instances using newtype
  - 6.9. Overlapping Instances
  - 6.10. Orphaned Instances
  - 6.11. Instance Dependencies
  - 6.12. Multi-Parametric Typeclasses
  - 6.13. Functional Dependency
- 7. Coding Typeclasses
  - 7.1. Coding Preparation
  - 7.2. Maybe Data Type
  - 7.3. Code for Maybe Data Type
  - 7.4. Writing Eq for Maybe
  - 7.5. Code for Eq for Maybe
  - 7.6. Writing Ord for Maybe
  - 7.7. Hint for Ord for Maybe
  - 7.8. Code for Ord for Maybe
  - 7.9. Writing >=
  - 7.10. Hint for >=
  - 7.11. Code for >=
  - 7.12. Writing Show for Maybe
  - 7.13. Code for Show for Maybe
  - 7.14. Deriving Eq, Ord and Show for Maybe
  - 7.15. Hint for Deriving
  - 7.16. Hint for Deriving Show
  - 7.17. Code for Eq, Ord and Show for Maybe
  - 7.18. Deriving Eq, Ord and Show for Either
  - 7.19. Writing Eq, Ord and Show for Either
  - 7.20. Creating Our Own Typeclass
  - 7.21. Hint for ToCSV
  - 7.22. Code for ToCSV
  - 7.23. Using ToCSV
  - 7.24. Another Hint for ToCSV
  - 7.25. Code for ToCSV
  - 7.26. Testing ToCSV
  - 7.27. Writing FromCSV
  - 7.28. Code for FromCSV
  - 7.29. Testing FromCSV
- 8. Abstract Algebra
  - 8.1. Binary Operators
    - 8.1.1. Associative Property
    - 8.1.2. Commutative Property
  - 8.2. Closure
  - 8.3. Magma
  - 8.4. Semigroup
  - 8.5. Semigroup Typeclass
  - 8.6. Monoid
  - 8.7. Monoid Typeclass
  - 8.8. Monoids in Programming vs Math
  - 8.9. Monoids in Programming
  - 8.10. Groups
  - 8.11. Group Typeclass
  - 8.12. Modular Arithmetic and Groups
  - 8.13. Abelian Group
  - 8.14. Abelian Group Type Alias
  - 8.15. Arithmetic Operators in PureScript
  - 8.16. Semiring
  - 8.17. Semiring Typeclass
  - 8.18. Semiring for Functions
  - 8.19. Semiring Laws for Functions
  - 8.20. Ring
  - 8.21. Ring Typeclass
  - 8.22. Commutative Ring Typeclass
  - 8.23. Euclidean Ring
  - 8.24. Summary
- 9. Coding Abstract Algebra
  - 9.1. Writing Semigroup Typeclass
  - 9.2. Hint for Semigroup Typeclass
  - 9.3. Code for Semigroup Typeclass
  - 9.4. Writing Monoid Typeclass
  - 9.5. Code for Monoid Typeclass
  - 9.6. Writing Semigroup for AndBool
  - 9.7. Hint for Semigroup for AndBool
  - 9.8. Code for Semigroup for AndBool
  - 9.9. Writing Monoid for AndBool
  - 9.10. Code for Monoid for AndBool
  - 9.11. Verify Semigroup Laws for AndBool
  - 9.12. Writing verifyAndBoolSemigroup
  - 9.13. Verify Monoid Laws for AndBool
  - 9.14. Writing verifyAndBoolMonoid
  - 9.15. Writing Semigroup and Monoid for OrBool
  - 9.16. Code for Semigroup and Monoid for OrBool
  - 9.17. Verify Semigroup and Monoid Laws for OrBool
  - 9.18. Code for Semigroup and Monoid Laws for OrBool
  - 9.19. Writing Mod4 Data Type
  - 9.20. Code for Mod4 Data Type
  - 9.21. Writing Semigroup for Mod4
  - 9.22. Hint for Semigroup for Mod4
  - 9.23. Code for Semigroup for Mod4
  - 9.24. Writing Monoid for Mod4
  - 9.25. Code for Monoid for Mod4
  - 9.26. Writing Group Typeclass
  - 9.27. Code for Group Typeclass
  - 9.28. Writing Group for Mod4
  - 9.29. Code for Group for Mod4
  - 9.30. Writing Eq and Show for Mod4
  - 9.31. Code for Eq and Show for Mod4
  - 9.32. Writing verifyMod4Semigroup for Mod4
  - 9.33. Code for verifyMod4Semigroup for Mod4
  - 9.34. Writing verifyMod4Monoid for Mod4
  - 9.35. Code for verifyMod4Monoid for Mod4
  - 9.36. Writing Semigroup for Maybe
  - 9.37. Writing Semigroup and Monoid for First
  - 9.38. Code for Semigroup and Monoid for First
  - 9.39. Writing Semigroup and Monoid for Last
  - 9.40. Code for Semigroup and Monoid for First
- 10. Folds
  - 10.1. Fold by other Names
  - 10.2. Foldable Typeclass
  - 10.3. Fold Associativity
  - 10.4. Foldable for List
  - 10.5. Rewriting length with Folds
- 11. Coding Folds
  - 11.1. Writing reverse
  - 11.2. Code for reverse
  - 11.3. Writing max
  - 11.4. Hint for max
  - 11.5. Code for max
  - 11.6. Writing findMax
  - 11.7. Code for findMax
  - 11.8. Improving findMax
  - 11.9. Improved findMax
  - 11.10. Code for findMax using Fold
  - 11.11. Code for findMax using NonEmptyList
  - 11.12. Postmortem of findMax and findMaxNE
  - 11.13. Writing findMaxNE using foldl1
  - 11.14. Code for findMaxNE using foldl1
  - 11.15. Writing foldl1
  - 11.16. Hint for foldl1
  - 11.17. Code for foldl1
  - 11.18. Writing sum
  - 11.19. Code for sum as a Recursive Function
  - 11.20. Code for sum as Tail Recursive
  - 11.21. Code for sum using foldl
  - 11.22. Hint for sum for Ints and Numbers
  - 11.23. Code for sum for Ints and Numbers
  - 11.24. Code for sum using Foldable
  - 11.25. Using sum with Tree
  - 11.26. Hint for Foldable for Tree
  - 11.27. Code for toList Instance for Tree
  - 11.28. Code for Foldable for Tree
  - 11.29. Improving on Foldable for Tree
- 12. Functors
  - 12.1. Defining ADTs
  - 12.2. Semantics
    - 12.2.1. Name
    - 12.2.2. Implicit Behavior
    - 12.2.3. Explicit Behavior
  - 12.3. Contexts
  - 12.4. Higher-kinded Types
  - 12.5. Functions with Simple Types
  - 12.6. Functors to the Rescue
  - 12.7. Two Perspectives of map
  - 12.8. The Power of Abstractions
  - 12.9. A Little Category Theory
  - 12.10. Concrete Examples in Hask
  - 12.11. Functors in Category Theory
  - 12.12. Functor Laws
  - 12.13. Verifying the Functor Laws for Maybe
  - 12.14. Functor Instance for Either
  - 12.15. Functor Instance for Choice
  - 12.16. Bifunctor Typeclass
  - 12.17. Bifunctors in Category Theory
  - 12.18. Bifunctor Laws
  - 12.19. Functors in Perspective
- 13. Coding Functors
  - 13.1. Writing Functor Instance for Maybe
  - 13.2. Code for Functor Instance of Maybe
  - 13.3. Writing Functor Instance for Either
  - 13.4. Code for Functor Instance of Either
  - 13.5. Writing Functor Instance for Tuple
  - 13.6. Code for Functor Instance of Tuple
  - 13.7. Writing Functor Instance for Threeple
  - 13.8. Writing Functor Instance for Threeple
  - 13.9. Validating the Functor Laws
  - 13.10. Writing Bifunctor Instance for Either
  - 13.11. Code for Bifunctor Instance for Either
  - 13.12. Writing Bifunctor Instance for Tuple
  - 13.13. Code for Bifunctor Instance for Tuple
  - 13.14. Writing Bifunctor Instance for Threeple
  - 13.15. Code for Bifunctor Instance for Threeple
  - 13.16. Validating the Bifunctor Laws
- 14. More Functors
  - 14.1. Functors of Values
  - 14.2. Functors of Functions
  - 14.3. Contravariant Functor
  - 14.4. Contravariant Laws
  - 14.5. Contravariant in Category Theory
  - 14.6. Choosing Functor or Contravariant
  - 14.7. Polarity
  - 14.8. Invariant Functor
  - 14.9. Invariant Laws
  - 14.10. Homomorphisms
  - 14.11. Natural Transformations
  - 14.12. Monoid Homomorphisms
  - 14.13. Isomorphisms
  - 14.14. Functor Instances for Function
  - 14.15. Profunctor
  - 14.16. Profunctor Laws
  - 14.17. Profunctor and Isomorphisms
  - 14.18. Profunctor Perspective
  - 14.19. Functor Summary
  - 14.20. Functor Intuition
- 15. Coding More Functors
  - 15.1. Writing the Predicate odd
  - 15.2. Code for the Predicate odd
  - 15.3. Writing a Predicate Type
  - 15.4. Code for a Predicate Type
  - 15.5. Code for runPredicate
  - 15.6. Writing Contravariant Instance for Predicate
  - 15.7. Code for Contravariant Instance for Predicate
  - 15.8. Folds and Moore Machines
  - 15.9. Hint for Profunctor for Moore
  - 15.10. Code for Profunctor for Moore
  - 15.11. Modeling Folds with Moore Machines
  - 15.12. Writing a Moore Machine that Folds
  - 15.13. Code for addr
  - 15.14. Code for a general addr
  - 15.15. Writing runFoldL
  - 15.16. Code for runFoldL
  - 15.17. Leveraging Moore’s Profunctor Instance
  - 15.18. Hint for sizer
  - 15.19. Code for sizer
  - 15.20. Power of the Functor
III: Advanced
- 16. Applicative Functors, Traversables and Alternatives
  - 16.1. Applicative in Haskell
  - 16.2. Applicative Functors in Category Theory
  - 16.3. Apply Laws
  - 16.4. Applicative Laws
  - 16.5. Applicative Instance for Maybe
  - 16.6. Applicative Instance for Product Types
  - 16.7. Applicative Instance for Sum Types
  - 16.8. An Applicative Example
  - 16.9. Applicative Effects
  - 16.10. Functors vs Applicatives with Effects
  - 16.11. Examples of Applicative Effects
  - 16.12. Applicative Effects and Commutativity
  - 16.13. Traversables
  - 16.14. Traversable for List
  - 16.15. A Few Words on Context
  - 16.16. Alt
  - 16.17. Alt Laws
  - 16.18. Plus
  - 16.19. Plus Laws
  - 16.20. Alternative Functor
- 17. Coding Applicatives
  - 17.1. Writing Applicative Instance for Maybe
  - 17.2. Code for Applicative Instance for Maybe
  - 17.3. Writing Applicative Instance for Either
  - 17.4. Code for Applicative Instance for Either
  - 17.5. Validation
  - 17.6. Using Validation
  - 17.7. Applicative Parsers
  - 17.8. Parsers in General
  - 17.9. Writing an Applicative Parser
  - 17.10. Looking Deeper at our Parser
  - 17.11. A Common Pattern with Our Parser
  - 17.12. Using Our Parser
- 18. Monads
  - 18.1. Side-effects
    - 18.1.1. Composing Side-effect Functions
    - 18.1.2. Composing Side-effect Function with Pure Ones
    - 18.1.3. Function Application with Side-effect Functions
  - 18.2. Debuggable Type
  - 18.3. Generalizing Debuggable
  - 18.4. We Created a Monad and More
  - 18.5. An Alternative Monad Implementation
  - 18.6. Back to PureScript’s Monad Implementation
  - 18.7. Recap Bind, Monad and Supporting Functions
  - 18.8. Haskell’s Monad Implementation
  - 18.9. Monad Laws
  - 18.10. Monad Instance for Maybe
  - 18.11. Working with Maybe Monad
  - 18.12. Do Notation
  - 18.13. Cheating with the Applicative Instance and ap
  - 18.14. Monad Instance for Either
  - 18.15. Working with Either Monad
  - 18.16. Adding Monad Instance for Validation
  - 18.17. Writer Monad
  - 18.18. Writer Helper Functions
  - 18.19. Parallel Computations
  - 18.20. Reader Monad
  - 18.21. State Monad
  - 18.22. Using State as a Monadic Validation
  - 18.23. The Kleisli Category
- 19. Coding Monads
  - 19.1. Writing Monad Instance for Maybe
  - 19.2. Code for Monad Instance for Maybe
  - 19.3. Writing Monad Instance for Either
  - 19.4. Code for Monad Instance for Either
  - 19.5. Monadic Parsers
  - 19.6. Coding with Monadic Parsers
  - 19.7. Writing a Date Parser
  - 19.8. How Does Parser Actually Work
  - 19.9. some and many Combinators
  - 19.10. Using some and many
  - 19.11. The RWS Monad
- 20. Monad Stacks
  - 20.1. Reducing the need for lift
  - 20.2. Monad Transformers and their APIs
  - 20.3. The Error Monad Transformer, ExceptT
  - 20.4. Monad Stack Order
  - 20.5. Coding with Monad Transformers
  - 20.6. Coding with Effect at the Base
  - 20.7. Coding WriterT
  - 20.8. Coding ReaderT
  - 20.9. Making ReaderT Easier to Use
  - 20.10. The Power of the Combinator
- 21. Coding Monad Transformers
  - 21.1. Writing the StateT Monad Transformer
  - 21.2. Type Holes and Undefined
  - 21.3. Back to Writing the StateT Monad Transformer
  - 21.4. Testing our StateT Implementation
  - 21.5. Problems with using StateT with ExceptT
  - 21.6. Guidelines for Using ExceptT
IV: Beyond
- 22. Synchronous and Asynchronous Effects
  - 22.1. Working with the Effect Monad
  - 22.2. Working with the Aff Monad
    - 22.2.1. Fibers
    - 22.2.2. Cancelers
    - 22.2.3. AVars
    - 22.2.4. Busses
- 23. Coding With Effects
  - 23.1. Simple AVar Program Specification
  - 23.2. Effects Program Specifications
    - 23.2.1. Creating a Random Number
    - 23.2.2. Making a Monad Stack
    - 23.2.3. Creating a Fiber
    - 23.2.4. Running a Monad Stack in a Fiber
    - 23.2.5. Making a Bus
    - 23.2.6. Publish to a Bus
    - 23.2.7. Subscribing to a Bus
  - 23.3. Coding our Effects Program
  - 23.4. Javascript Runtime with AVars and Busses
- 24. JSON and Ajax
  - 24.1. Generic JSON Encoding and Decoding
    - 24.1.1. Foreign Module
    - 24.1.2. Foreign.Generic Module
    - 24.1.3. Foreign.Generic.Class Module
  - 24.2. Argonaut JSON Encoding and Decoding
  - 24.3. Ajax
    - 24.3.1. GET Request
    - 24.3.2. POST Request
- 25. Coding With Ajax and JSON
  - 25.1. Ajax Program Specifications
  - 25.2. Coding Ajax and JSON with Foreign
    - 25.2.1. Encoding and Sending to the Echo Server
    - 25.2.2. Decoding the Response Modeled with Reversed Names
    - 25.2.3. Decoding the Response Using Argonaut
    - 25.2.4. Serial and Parallel Aff
    - 25.2.5. Using Parallel with Ajax
- 26. Foreign Function Interface (FFI)
  - 26.1. FFIs That Return PureScript Types
  - 26.2. FFIs and Effect
  - 26.3. FFIs and Aff
- 27. Coding With FFIs
  - 27.1. Wrapping an NPM library
  - 27.2. Reversing JSON Keys in Javascript
- 28. Writing a Backend using HTTPure
  - 28.1. A Brief Primer on HTTPure
    - 28.1.1. Creating an HTTP Server
  - 28.2. Routers
  - 28.3. API For a Front-end Application
  - 28.4. Modeling the API
  - 28.5. Coding the Server’s Infrastructure
  - 28.6. Coding the Account Handler
    - 28.6.1. Coding loadAccounts
    - 28.6.2. Coding createAccount
  - 28.7. Coding the Account Manager
    - 28.7.1. Code for Password Hash
    - 28.7.2. Coding startup and shutdown for Account Manager
    - 28.7.3. Coding verifyLogon
    - 28.7.4. Finishing the logon Request
    - 28.7.5. Fleshing out router
  - 28.8. Coding the Session Manager
    - 28.8.1. Code for startup, shutdown and verifySession
  - 28.9. Server Logging
  - 28.10. Coding the API
    - 28.10.1. Coding LogoffRequest API Handler
    - 28.10.2. Coding CreateUserRequest API Handler
    - 28.10.3. Improving Our Parser
    - 28.10.4. Coding QueryUsers API Handler
  - 28.11. Servers in PureScript
- 29. Building Front-ends using Halogen
  - 29.1. Halogen Component Overview
    - 29.1.1. State
    - 29.1.2. Actions
    - 29.1.3. Queries
    - 29.1.4. Inputs
    - 29.1.5. Outputs
    - 29.1.6. Emitters
    - 29.1.7. Lifecycle
    - 29.1.8. Slots
    - 29.1.9. Halogen Model
  - 29.2. Halogen Example Application
    - 29.2.1. Creating New Project
    - 29.2.2. Writing a Counter Component
    - 29.2.3. Rendering the Counter Component
    - 29.2.4. Counter Component Query Algebra
    - 29.2.5. Counter Component as a Child Component
    - 29.2.6. Emitters
- 30. Writing a Front End using Halogen
  - 30.1. Halogen CSS Library Setup
  - 30.2. Hash Routing
    - 30.2.1. Defining Routes
  - 30.3. Application Monad
  - 30.4. Capabilities
  - 30.5. Capability Implementations
  - 30.6. Router Component
  - 30.7. Page Component
  - 30.8. Logon Page
  - 30.9. Calling the Backend
    - 30.9.1. CORS Solution
    - 30.9.2. Static File Server Solution
  - 30.10. ChangePassword Page
  - 30.11. Users Page
  - 30.12. Modal Dialog Component
  - 30.13. Message Modal Component
  - 30.14. Customizing the Modal Dialog Component
  - 30.15. Create Users Modal Component
  - 30.16. Logoff Page
Appendix A: Epilogue