Real World Haskell. Code You Can Believe In

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• Real World Haskell
• Dedication
• A Note Regarding Supplemental Files
• Preface
  • Have We Got a Deal for You!
    • Novelty
    • Power
    • Enjoyment
  • What to Expect from This Book
    • A Little Bit About You
  • What to Expect from Haskell
    • Compared to Traditional Static Languages
    • Compared to Modern Dynamic Languages
    • Haskell in Industry and Open Source
    • Compilation, Debugging, and Performance Analysis
    • Bundled and Third-Party Libraries
  • A Brief Sketch of Haskells History
    • Prehistory
    • Early Antiquity
    • The Modern Era
  • Helpful Resources
    • Reference Material
    • Applications and Libraries
    • The Haskell Community
  • Conventions Used in This Book
  • Using Code Examples
  • Safari Books Online
  • How to Contact Us
  • Acknowledgments
    • Bryan
    • John
    • Don
    • Thank You to Our Reviewers
• 1. Getting Started
  • Your Haskell Environment
  • Getting Started with ghci, the Interpreter
  • Basic Interaction: Using ghci as a Calculator
    • Simple Arithmetic
    • An Arithmetic Quirk: Writing Negative Numbers
    • Boolean Logic, Operators, and Value Comparisons
    • Operator Precedence and Associativity
    • Undefined Values, and Introducing Variables
    • Dealing with Precedence and Associativity Rules
  • Command-Line Editing in ghci
  • Lists
    • Operators on Lists
  • Strings and Characters
  • First Steps with Types
  • A Simple Program
• 2. Types and Functions
  • Why Care About Types?
  • Haskells Type System
    • Strong Types
    • Static Types
    • Type Inference
  • What to Expect from the Type System
  • Some Common Basic Types
  • Function Application
  • Useful Composite Data Types: Lists and Tuples
  • Functions over Lists and Tuples
    • Passing an Expression to a Function
  • Function Types and Purity
  • Haskell Source Files, and Writing Simple Functions
    • Just What Is a Variable, Anyway?
    • Conditional Evaluation
  • Understanding Evaluation by Example
    • Lazy Evaluation
    • A More Involved Example
    • Recursion
    • Ending the Recursion
    • Returning from the Recursion
    • What Have We Learned?
  • Polymorphism in Haskell
    • Reasoning About Polymorphic Functions
    • Further Reading
  • The Type of a Function of More Than One Argument
  • Why the Fuss over Purity?
  • Conclusion
• 3. Defining Types, Streamlining Functions
  • Defining a New Data Type
    • Naming Types and Values
  • Type Synonyms
  • Algebraic Data Types
    • Tuples, Algebraic Data Types, and When to Use Each
    • Analogues to Algebraic Data Types in Other Languages
      • The structure
      • The enumeration
      • The discriminated union
  • Pattern Matching
    • Construction and Deconstruction
    • Further Adventures
    • Variable Naming in Patterns
    • The Wild Card Pattern
    • Exhaustive Patterns and Wild Cards
  • Record Syntax
  • Parameterized Types
  • Recursive Types
  • Reporting Errors
    • A More Controlled Approach
  • Introducing Local Variables
    • Shadowing
    • The where Clause
    • Local Functions, Global Variables
  • The Offside Rule and Whitespace in an Expression
    • A Note About Tabs Versus Spaces
    • The Offside Rule Is Not Mandatory
  • The case Expression
  • Common Beginner Mistakes with Patterns
    • Incorrectly Matching Against a Variable
    • Incorrectly Trying to Compare for Equality
  • Conditional Evaluation with Guards
• 4. Functional Programming
  • Thinking in Haskell
  • A Simple Command-Line Framework
  • Warming Up: Portably Splitting Lines of Text
    • A Line-Ending Conversion Program
  • Infix Functions
  • Working with Lists
    • Basic List Manipulation
    • Safely and Sanely Working with Crashy Functions
    • Partial and Total Functions
    • More Simple List Manipulations
    • Working with Sublists
    • Searching Lists
    • Working with Several Lists at Once
    • Special String-Handling Functions
  • How to Think About Loops
    • Explicit Recursion
    • Transforming Every Piece of Input
    • Mapping over a List
    • Selecting Pieces of Input
    • Computing One Answer over a Collection
    • The Left Fold
    • Why Use Folds, Maps, and Filters?
    • Folding from the Right
    • Left Folds, Laziness, and Space Leaks
    • Further Reading
  • Anonymous (lambda) Functions
  • Partial Function Application and Currying
    • Sections
  • As-patterns
  • Code Reuse Through Composition
    • Use Your Head Wisely
  • Tips for Writing Readable Code
  • Space Leaks and Strict Evaluation
    • Avoiding Space Leaks with seq
    • Learning to Use seq
• 5. Writing a Library: Working with JSON Data
  • A Whirlwind Tour of JSON
  • Representing JSON Data in Haskell
  • The Anatomy of a Haskell Module
  • Compiling Haskell Source
  • Generating a Haskell Program and Importing Modules
  • Printing JSON Data
  • Type Inference Is a Double-Edged Sword
  • A More General Look at Rendering
  • Developing Haskell Code Without Going Nuts
  • Pretty Printing a String
  • Arrays and Objects, and the Module Header
  • Writing a Module Header
  • Fleshing Out the Pretty-Printing Library
    • Compact Rendering
    • True Pretty Printing
    • Following the Pretty Printer
  • Creating a Package
    • Writing a Package Description
    • GHCs Package Manager
    • Setting Up, Building, and Installing
  • Practical Pointers and Further Reading
• 6. Using Typeclasses
  • The Need for Typeclasses
  • What Are Typeclasses?
  • Declaring Typeclass Instances
  • Important Built-in Typeclasses
    • Show
    • Read
    • Serialization with read and show
    • Numeric Types
    • Equality, Ordering, and Comparisons
  • Automatic Derivation
  • Typeclasses at Work: Making JSON Easier to Use
    • More Helpful Errors
    • Making an Instance with a Type Synonym
  • Living in an Open World
    • When Do Overlapping Instances Cause Problems?
    • Relaxing Some Restrictions on Typeclasses
    • How Does Show Work for Strings?
  • How to Give a Type a New Identity
    • Differences Between Data and Newtype Declarations
    • Summary: The Three Ways of Naming Types
  • JSON Typeclasses Without Overlapping Instances
  • The Dreaded Monomorphism Restriction
  • Conclusion
• 7. I/O
  • Classic I/O in Haskell
    • Pure Versus I/O
    • Why Purity Matters
  • Working with Files and Handles
    • More on openFile
    • Closing Handles
    • Seek and Tell
    • Standard Input, Output, and Error
    • Deleting and Renaming Files
    • Temporary Files
  • Extended Example: Functional I/O and Temporary Files
  • Lazy I/O
    • hGetContents
    • readFile and writeFile
    • A Word on Lazy Output
    • interact
      • Filters with interact
  • The IO Monad
    • Actions
    • Sequencing
    • The True Nature of Return
  • Is Haskell Really Imperative?
  • Side Effects with Lazy I/O
  • Buffering
    • Buffering Modes
    • Flushing The Buffer
  • Reading Command-Line Arguments
  • Environment Variables
• 8. Efficient File Processing, Regular Expressions, and Filename Matching
  • Efficient File Processing
    • Binary I/O and Qualified Imports
    • Text I/O
  • Filename Matching
  • Regular Expressions in Haskell
    • The Many Types of Result
  • More About Regular Expressions
    • Mixing and Matching String Types
    • Other Things You Should Know
  • Translating a glob Pattern into a Regular Expression
  • An important Aside: Writing Lazy Functions
  • Making Use of Our Pattern Matcher
  • Handling Errors Through API Design
  • Putting Our Code to Work
• 9. I/O Case Study: A Library for Searching the Filesystem
  • The find Command
  • Starting Simple: Recursively Listing a Directory
    • Revisiting Anonymous and Named Functions
    • Why Provide Both mapM and forM?
  • A Naive Finding Function
  • Predicates: From Poverty to Riches, While Remaining Pure
  • Sizing a File Safely
    • The Acquire-Use-Release Cycle
  • A Domain-Specific Language for Predicates
    • Avoiding Boilerplate with Lifting
    • Gluing Predicates Together
    • Defining and Using New Operators
  • Controlling Traversal
  • Density, Readability, and the Learning Process
  • Another Way of Looking at Traversal
  • Useful Coding Guidelines
    • Common Layout Styles
• 10. Code Case Study: Parsing a Binary Data Format
  • Grayscale Files
  • Parsing a Raw PGM File
  • Getting Rid of Boilerplate Code
  • Implicit State
    • The Identity Parser
    • Record Syntax, Updates, and Pattern Matching
    • A More Interesting Parser
    • Obtaining and Modifying the Parse State
    • Reporting Parse Errors
    • Chaining Parsers Together
  • Introducing Functors
    • Constraints on Type Definitions Are Bad
    • Infix Use of fmap
    • Flexible Instances
    • Thinking More About Functors
  • Writing a Functor Instance for Parse
  • Using Functors for Parsing
  • Rewriting Our PGM Parser
  • Future Directions
• 11. Testing and Quality Assurance
  • QuickCheck: Type-Based Testing
    • Testing for Properties
    • Testing Against a Model
  • Testing Case Study: Specifying a Pretty Printer
    • Generating Test Data
    • Testing Document Construction
    • Using Lists as a Model
    • Putting It All Together
  • Measuring Test Coverage with HPC
• 12. Barcode Recognition
  • A Little Bit About Barcodes
    • EAN-13 Encoding
  • Introducing Arrays
    • Arrays and Laziness
    • Folding over Arrays
    • Modifying Array Elements
  • Encoding an EAN-13 Barcode
  • Constraints on Our Decoder
  • Divide and Conquer
  • Turning a Color Image into Something Tractable
    • Parsing a Color Image
    • Grayscale Conversion
    • Grayscale to Binary and Type Safety
  • What Have We Done to Our Image?
  • Finding Matching Digits
    • Run Length Encoding
    • Scaling Run Lengths, and Finding Approximate Matches
    • List Comprehensions
    • Remembering a Matchs Parity
      • Another kind of laziness, of the keyboarding variety
    • Chunking a List
    • Generating a List of Candidate Digits
  • Life Without Arrays or Hash Tables
    • A Forest of Solutions
    • A Brief Introduction to Maps
      • Type constraints
      • Partial application awkwardness
      • Getting started with the API
    • Further Reading
  • Turning Digit Soup into an Answer
    • Solving for Check Digits in Parallel
    • Completing the Solution Map with the First Digit
    • Finding the Correct Sequence
  • Working with Row Data
  • Pulling It All Together
  • A Few Comments on Development Style
• 13. Data Structures
  • Association Lists
  • Maps
  • Functions Are Data, Too
  • Extended Example: /etc/passwd
  • Extended Example: Numeric Types
    • First Steps
    • Completed Code
  • Taking Advantage of Functions as Data
    • Turning Difference Lists into a Proper Library
    • Lists, Difference Lists, and Monoids
  • General-Purpose Sequences
• 14. Monads
  • Revisiting Earlier Code Examples
    • Maybe Chaining
    • Implicit State
  • Looking for Shared Patterns
  • The Monad Typeclass
  • And Now, a Jargon Moment
  • Using a New Monad: Show Your Work!
    • Information Hiding
    • Controlled Escape
    • Leaving a Trace
    • Using the Logger Monad
  • Mixing Pure and Monadic Code
  • Putting a Few Misconceptions to Rest
  • Building the Logger Monad
    • Sequential Logging, Not Sequential Evaluation
    • The Writer Monad
  • The Maybe Monad
    • Executing the Maybe Monad
    • Maybe at Work, and Good API Design
  • The List Monad
    • Understanding the List Monad
    • Putting the List Monad to Work
  • Desugaring of do Blocks
    • Monads as a Programmable Semicolon
    • Why Go Sugar-Free?
  • The State Monad
    • Almost a State Monad
    • Reading and Modifying the State
    • Will the Real State Monad Please Stand Up?
    • Using the State Monad: Generating Random Values
    • A First Attempt at Purity
    • Random Values in the State Monad
    • Running the State Monad
    • What About a Bit More State?
  • Monads and Functors
    • Another Way of Looking at Monads
  • The Monad Laws and Good Coding Style
• 15. Programming with Monads
  • Golfing Practice: Association Lists
  • Generalized Lifting
  • Looking for Alternatives
    • The Name mplus Does Not Imply Addition
    • Rules for Working with MonadPlus
    • Failing Safely with MonadPlus
  • Adventures in Hiding the Plumbing
    • Supplying Random Numbers
    • Another Round of Golf
  • Separating Interface from Implementation
    • Multiparameter Typeclasses
    • Functional Dependencies
    • Rounding Out Our Module
    • Programming to a Monads Interface
  • The Reader Monad
  • A Return to Automated Deriving
  • Hiding the IO Monad
    • Using a newtype
    • Designing for Unexpected Uses
    • Using Typeclasses
    • Isolation and Testing
    • The Writer Monad and Lists
    • Arbitrary I/O Revisited
• 16. Using Parsec
  • First Steps with Parsec: Simple CSV Parsing
  • The sepBy and endBy Combinators
  • Choices and Errors
    • Lookahead
    • Error Handling
  • Extended Example: Full CSV Parser
  • Parsec and MonadPlus
  • Parsing a URL-Encoded Query String
  • Supplanting Regular Expressions for Casual Parsing
  • Parsing Without Variables
  • Applicative Functors for Parsing
  • Applicative Parsing by Example
  • Parsing JSON Data
  • Parsing a HTTP Request
    • Backtracking and Its Discontents
    • Parsing Headers
• 17. Interfacing with C: The FFI
  • Foreign Language Bindings: The Basics
    • Be Careful of Side Effects
    • A High-Level Wrapper
  • Regular Expressions for Haskell: A Binding for PCRE
    • Simple Tasks: Using the C Preprocessor
    • Binding Haskell to C with hsc2hs
    • Adding Type Safety to PCRE
    • Binding to Constants
    • Automating the Binding
  • Passing String Data Between Haskell and C
    • Typed Pointers
    • Memory Management: Let the Garbage Collector Do the Work
    • A High-Level Interface: Marshaling Data
    • Marshaling ByteStrings
    • Allocating Local C Data: The Storable Class
    • Putting It All Together
  • Matching on Strings
    • Extracting Information About the Pattern
    • Pattern Matching with Substrings
    • The Real Deal: Compiling and Matching Regular Expressions
• 18. Monad Transformers
  • Motivation: Boilerplate Avoidance
  • A Simple Monad Transformer Example
  • Common Patterns in Monads and Monad Transformers
  • Stacking Multiple Monad Transformers
    • Hiding Our Work
  • Moving Down the Stack
    • When Explicit Lifting Is Necessary
  • Understanding Monad Transformers by Building One
    • Creating a Monad Transformer
    • More Typeclass Instances
    • Replacing the Parse Type with a Monad Stack
  • Transformer Stacking Order Is Important
  • Putting Monads and Monad Transformers into Perspective
    • Interference with Pure Code
    • Overdetermined Ordering
    • Runtime Overhead
    • Unwieldy Interfaces
    • Pulling It All Together
• 19. Error Handling
  • Error Handling with Data Types
    • Use of Maybe
      • Loss and preservation of laziness
      • Usage of the Maybe monad
    • Use of Either
      • Custom data types for errors
      • Monadic use of Either
  • Exceptions
    • First Steps with Exceptions
    • Laziness and Exception Handling
    • Using handle
    • Selective Handling of Exceptions
    • I/O Exceptions
    • Throwing Exceptions
    • Dynamic Exceptions
  • Error Handling in Monads
    • A Tiny Parsing Framework
• 20. Systems Programming in Haskell
  • Running External Programs
  • Directory and File Information
  • Program Termination
  • Dates and Times
    • ClockTime and CalendarTime
      • Using ClockTime
      • Using CalendarTime
      • TimeDiff for ClockTime
    • File Modification Times
  • Extended Example: Piping
    • Using Pipes for Redirection
    • Better Piping
    • Final Words on Pipes
• 21. Using Databases
  • Overview of HDBC
  • Installing HDBC and Drivers
  • Connecting to Databases
  • Transactions
  • Simple Queries
  • SqlValue
  • Query Parameters
  • Prepared Statements
  • Reading Results
    • Reading with Statements
    • Lazy Reading
  • Database Metadata
  • Error Handling
• 22. Extended Example: Web Client Programming
  • Basic Types
  • The Database
  • The Parser
  • Downloading
  • Main Program
• 23. GUI Programming with gtk2hs
  • Installing gtk2hs
  • Overview of the GTK+ Stack
  • User Interface Design with Glade
    • Glade Concepts
  • Event-Driven Programming
  • Initializing the GUI
  • The Add Podcast Window
  • Long-Running Tasks
  • Using Cabal
• 24. Concurrent and Multicore Programming
  • Defining Concurrency and Parallelism
  • Concurrent Programming with Threads
    • Threads Are Nondeterministic
    • Hiding Latency
  • Simple Communication Between Threads
  • The Main Thread and Waiting for Other Threads
    • Safely Modifying an MVar
    • Safe Resource Management: A Good Idea, and Easy Besides
    • Finding the Status of a Thread
    • Writing Tighter Code
  • Communicating over Channels
  • Useful Things to Know About
    • MVar and Chan Are Nonstrict
    • Chan Is Unbounded
  • Shared-State Concurrency Is Still Hard
    • Deadlock
    • Starvation
    • Is There Any Hope?
  • Using Multiple Cores with GHC
    • Runtime Options
    • Finding the Number of Available Cores from Haskell
    • Choosing the Right Runtime
  • Parallel Programming in Haskell
    • Normal Form and Head Normal Form
    • Sequential Sorting
    • Transforming Our Code into Parallel Code
    • Knowing What to Evaluate in Parallel
    • What Promises Does par Make?
    • Running Our Code and Measuring Performance
    • Tuning for Performance
  • Parallel Strategies and MapReduce
    • Separating Algorithm from Evaluation
    • Separating Algorithm from Strategy
    • Writing a Simple MapReduce Definition
    • MapReduce and Strategies
    • Sizing Work Appropriately
      • Mitigating the risks of lazy I/O
    • Efficiently Finding Line-Aligned Chunks
    • Counting Lines
    • Finding the Most Popular URLs
    • Conclusions
• 25. Profiling and Optimization
  • Profiling Haskell Programs
    • Collecting Runtime Statistics
    • Time Profiling
    • Space Profiling
  • Controlling Evaluation
    • Strictness and Tail Recursion
    • Adding Strictness
      • Normal form reduction
      • Bang patterns
      • Strict data types
  • Understanding Core
  • Advanced Techniques: Fusion
    • Tuning the Generated Assembly
    • Conclusions
• 26. Advanced Library Design: Building a Bloom Filter
  • Introducing the Bloom Filter
  • Use Cases and Package Layout
  • Basic Design
    • Unboxing, Lifting, and Bottom
  • The ST Monad
  • Designing an API for Qualified Import
  • Creating a Mutable Bloom Filter
  • The Immutable API
  • Creating a Friendly Interface
    • Re-Exporting Names for Convenience
    • Hashing Values
    • Turning Two Hashes into Many
    • Implementing the Easy Creation Function
  • Creating a Cabal Package
    • Dealing with Different Build Setups
    • Compilation Options and Interfacing to C
  • Testing with QuickCheck
    • Polymorphic Testing
    • Writing Arbitrary Instances for ByteStrings
    • Are Suggested Sizes Correct?
  • Performance Analysis and Tuning
    • Profile-Driven Performance Tuning
• 27. Sockets and Syslog
  • Basic Networking
  • Communicating with UDP
    • UDP Client Example: syslog
    • UDP Syslog Server
  • Communicating with TCP
    • Handling Multiple TCP Streams
    • TCP Syslog Server
    • TCP Syslog Client
• 28. Software Transactional Memory
  • The Basics
  • Some Simple Examples
  • STM and Safety
  • Retrying a Transaction
    • What Happens When We Retry?
  • Choosing Between Alternatives
    • Using Higher Order Code with Transactions
  • I/O and STM
  • Communication Between Threads
  • A Concurrent Web Link Checker
    • Checking a Link
    • Worker Threads
    • Finding Links
    • Command-Line Parsing
    • Pattern Guards
  • Practical Aspects of STM
    • Getting Comfortable with Giving Up Control
    • Using Invariants
• A. Installing GHC and Haskell Libraries
  • Installing GHC
    • Windows
    • Mac OS X
      • Alternatives
    • Ubuntu and Debian Linux
    • Fedora Linux
    • FreeBSD
  • Installing Haskell Software
    • Automated Download and Installation with cabal
      • Installing cabal
      • Updating cabals package list
      • Installing a library or program
    • Building Packages by Hand
• B. Characters, Strings, and Escaping Rules
  • Writing Character and String Literals
  • International Language Support
  • Escaping Text
    • Single-Character Escape Codes
    • Multiline String Literals
    • ASCII Control Codes
    • Control-with-Character Escapes
    • Numeric Escapes
    • The Zero-Width Escape Sequence
• Index
• About the Authors
• Colophon
• Copyright

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