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Clojure Programming

Cover of Clojure Programming by Chas Emerick... Published by O'Reilly Media, Inc.
  1. Clojure Programming
  2. SPECIAL OFFER: Upgrade this ebook with O’Reilly
  3. Preface
    1. Who Is This Book For?
      1. Engaged Java Developers
      2. Ruby, Python, and Other Developers
    2. How to Read This Book
      1. Start with Practical Applications of Clojure
      2. Start from the Ground Up with Clojure’s Foundational Concepts
    3. Who’s “We”?
      1. Chas Emerick
      2. Brian Carper
      3. Christophe Grand
    4. Acknowledgments
      1. And Last, but Certainly Far from Least
    5. Conventions Used in This Book
    6. Using Code Examples
    7. Safari® Books Online
    8. How to Contact Us
  4. 1. Down the Rabbit Hole
    1. Why Clojure?
    2. Obtaining Clojure
    3. The Clojure REPL
    4. No, Parentheses Actually Won’t Make You Go Blind
    5. Expressions, Operators, Syntax, and Precedence
    6. Homoiconicity
    7. The Reader
      1. Scalar Literals
      2. Comments
      3. Whitespace and Commas
      4. Collection Literals
      5. Miscellaneous Reader Sugar
    8. Namespaces
    9. Symbol Evaluation
    10. Special Forms
      1. Suppressing Evaluation: quote
      2. Code Blocks: do
      3. Defining Vars: def
      4. Local Bindings: let
      5. Destructuring (let, Part 2)
      6. Creating Functions: fn
      7. Conditionals: if
      8. Looping: loop and recur
      9. Referring to Vars: var
      10. Java Interop: . and new
      11. Exception Handling: try and throw
      12. Specialized Mutation: set!
      13. Primitive Locking: monitor-enter and monitor-exit
    11. Putting It All Together
      1. eval
    12. This Is Just the Beginning
  5. I. Functional Programming and Concurrency
    1. 2. Functional Programming
      1. What Does Functional Programming Mean?
      2. On the Importance of Values
      3. First-Class and Higher-Order Functions
      4. Composition of Function(ality)
      5. Pure Functions
      6. Functional Programming in the Real World
    2. 3. Collections and Data Structures
      1. Abstractions over Implementations
      2. Concise Collection Access
      3. Data Structure Types
      4. Immutability and Persistence
      5. Metadata
      6. Putting Clojure’s Collections to Work
      7. In Summary
    3. 4. Concurrency and Parallelism
      1. Shifting Computation Through Time and Space
      2. Parallelism on the Cheap
      3. State and Identity
      4. Clojure Reference Types
      5. Classifying Concurrent Operations
      6. Atoms
      7. Notifications and Constraints
      8. Refs
      9. Vars
      10. Agents
      11. Using Java’s Concurrency Primitives
      12. Final Thoughts
  6. II. Building Abstractions
    1. 5. Macros
      1. What Is a Macro?
      2. Writing Your First Macro
      3. Debugging Macros
      4. Syntax
      5. When to Use Macros
      6. Hygiene
      7. Common Macro Idioms and Patterns
      8. The Implicit Arguments: &env and &form
      9. In Detail: -> and ->>
      10. Final Thoughts
    2. 6. Datatypes and Protocols
      1. Protocols
      2. Extending to Existing Types
      3. Defining Your Own Types
      4. Implementing Protocols
      5. Protocol Introspection
      6. Protocol Dispatch Edge Cases
      7. Participating in Clojure’s Collection Abstractions
      8. Final Thoughts
    3. 7. Multimethods
      1. Multimethods Basics
      2. Toward Hierarchies
      3. Hierarchies
      4. Making It Really Multiple!
      5. A Few More Things
      6. Final Thoughts
  7. III. Tools, Platform, and Projects
    1. 8. Organizing and Building Clojure Projects
      1. Project Geography
      2. Build
      3. Final Thoughts
    2. 9. Java and JVM Interoperability
      1. The JVM Is Clojure’s Foundation
      2. Using Java Classes, Methods, and Fields
      3. Handy Interop Utilities
      4. Exceptions and Error Handling
      5. Type Hinting for Performance
      6. Arrays
      7. Defining Classes and Implementing Interfaces
      8. Using Clojure from Java
      9. Collaborating Partners
    3. 10. REPL-Oriented Programming
      1. Interactive Development
      2. Tooling
      3. Debugging, Monitoring, and Patching Production in the REPL
      4. Limitations to Redefining Constructs
      5. In Summary
  8. IV. Practicums
    1. 11. Numerics and Mathematics
      1. Clojure Numerics
      2. Clojure Mathematics
      3. Equality and Equivalence
      4. Optimizing Numeric Performance
      5. Visualizing the Mandelbrot Set in Clojure
    2. 12. Design Patterns
      1. Dependency Injection
      2. Strategy Pattern
      3. Chain of Responsibility
      4. Aspect-Oriented Programming
      5. Final Thoughts
    3. 13. Testing
      1. Immutable Values and Pure Functions
      2. clojure.test
      3. Growing an HTML DSL
      4. Relying upon Assertions
    4. 14. Using Relational Databases
      1. clojure.java.jdbc
      2. Korma
      3. Hibernate
      4. Final Thoughts
    5. 15. Using Nonrelational Databases
      1. Getting Set Up with CouchDB and Clutch
      2. Basic CRUD Operations
      3. Views
      4. _changes: Abusing CouchDB as a Message Queue
      5. À la Carte Message Queues
      6. Final Thoughts
    6. 16. Clojure and the Web
      1. The “Clojure Stack”
      2. The Foundation: Ring
      3. Routing Requests with Compojure
      4. Templating
      5. Final Thoughts
    7. 17. Deploying Clojure Web Applications
      1. Java and Clojure Web Architecture
      2. Running Web Apps Locally
      3. Web Application Deployment
      4. Going Beyond Simple Web Application Deployment
  9. V. Miscellanea
    1. 18. Choosing Clojure Type Definition Forms Wisely
    2. 19. Introducing Clojure into Your Workplace
      1. Just the Facts…
      2. Emphasize Productivity
      3. Emphasize Community
      4. Be Prudent
    3. 20. What’s Next?
      1. (dissoc Clojure 'JVM)
      2. 4Clojure
      3. Overtone
      4. core.logic
      5. Pallet
      6. Avout
      7. Clojure on Heroku
  10. Index
  11. About the Authors
  12. Colophon
  13. SPECIAL OFFER: Upgrade this ebook with O’Reilly
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Relying upon Assertions

Our HTML generation functions are decent, but someone somewhere will inevitably attempt to abuse the API. For example, the Clojure-standard representation of XML (as produced by clojure.xml) looks like this:

{:tag :a, :attrs {:href "http://clojure.org"}, :content ["Clojure"]}

That’s quite different than our vector-based HTML representation. Unsurprisingly, html will do odd things with this map, since it’s not at all what it’s expecting:

(html {:tag :a, :attrs {:href "http://clojure.org"}, :content ["Clojure"]})
;= "{:content [\"Clojure\"], :attrs {:href \"http://clojure.org\"}, :tag :a}"

Cripes, it returns a string! That’s appropriate insofar as we somewhat lazily use html recursively to process the contents of element vectors, but this particular result is clearly not useful if we imagine a user that (perhaps reasonably) thinks she might be able to serialize a clojure.xml data structure to an HTML string using our html function. This is a situation where we’d like to fail as quickly as possible.

Enter assertions. Assertions test a condition and throw an error if the condition is not true:

(defn attrs
  [attrs]
  (assert (or (map? attr-map)                                    1 (nil? attr-map)) "attr-map must be nil, or a map") (->> attrs (mapcat (fn [[k v]] [\space (name k) "=\"" v "\""])) (apply str))) (attrs "hi") ;= #<AssertionError java.lang.AssertionError: ;= Assert failed: attr-map must be nil, or ...

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