Polyglot and Poly-paradigm Programming for Better Agility

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Polyglot and Poly-paradigm Programming for Better Agility

  1. 1. Polyglot and Poly-paradigm Programming for Better Agility Dean Wampler dean@deanwampler.com @deanwampler 1
  2. 2. 2 Co-author, Programming Scala programmingscala.com
  3. 3. Polyglot: many languages Poly-paradigm: many modularity paradigms 3
  4. 4. Today’s applications: •Are networked, •Have graphical and “service” interfaces, flickr.com/photos/jerryjohn 4
  5. 5. Today’s applications: •Persist data, •Must be resilient and secure, •Must scale, flickr.com/photos/jerryjohn 5
  6. 6. Today’s applications: •… and must do all that by Friday. flickr.com/photos/jerryjohn 6
  7. 7. flickr.com/photos/deanwampler Mono- paradigm: Object-Oriented Programming: right for all problems? 7
  8. 8. twitter.com/photos/watchsmart Is one language best for all domains? Monolingual 8
  9. 9. Symptoms of Monocultures • Why is there so much XML in my Java? • Why do I have similar persistence code scattered all over my code base? • How can I scale my application by a factor of 1000! • My application is hard to extend! • I can’t respond quickly when requirements change! 9
  10. 10. switch (elementItem) { case "header1:SearchBox" : { __doPostBack('header1:goSearch',''); break; } case "Text1": { window.event.returnValue=false; window.event.cancel = true; document.forms[0].elements[n+1].focus(); break; } ... thedailywtf.com Pervasive IT problem: Too much code! 10
  11. 11. Solutions The symptoms reflect common problems with similar solutions. 11
  12. 12. I need extensibility and agility. Specific problem #1 flickr.com/photos/arrrika 12
  13. 13. Symptoms •Features take too long to implement. •We can’t react fast enough to change. •Uses want to customize the system themselves.13
  14. 14. Solution Application Kernel of Components User Scripts Built-in Scripts (C Components) + (Lisp scripts) = Emacs 14
  15. 15. Components + Scripts = Applications see John Ousterhout, IEEE Computer, March ’98 15
  16. 16. Kernel Components •Statically-typed language: •C, C++, Java, C#, ... •Compiled for speed, efficiency. •Access OS services, 3rd-party libraries. •Lower developer productivity. 16
  17. 17. Scripts •Dynamically-typed language: •Ruby, Python, JavaScript, Lua, ... •Interpreted for agility. •Performance less important. •Glue together components. •Raise developer productivity.17
  18. 18. In practice, the boundaries between components and scripts are not so distinct... 18
  19. 19. Ola Bini’s Three Layers •Domain layer •Internal and External DSLs. •Dynamic layer •e.g., JRuby, application code •Stable layer •JVM + generic libraries19
  20. 20. Other Examples of This Approach •UNIX/Linux + shells. •Also find, make, grep, ... •Have their own DSLs. •Tektronix Oscilloscopes: C + Smalltalk. 20
  21. 21. Other Examples... • Adobe Lightroom: C++ + Lua. • 40-50% written in Lua. • NRAOTelescopes: C + Python. • Google Android: Linux + libraries (C) + Java. 21
  22. 22. <view-state id="displayResults" view="/searchResults.jsp"> <render-actions> <bean-action bean="phonebook" method="search"> <method-arguments> <argument expression="searchCriteria"/> </method-arguments> <method-result name="results" scope="flash"/> </bean-action> </render-actions> <transition on="select" to="browseDetails"/> <transition on="newSearch" to="enterCriteria"/> </view-state> </flow> XML in Java Why not replace XML with JavaScript , Groovy or JRuby?? 22
  23. 23. Other Examples: MultilingualVM’s • On the JVM: • JRuby, Groovy, Jython, Scala. • Ruby on Rails on JRuby. 23
  24. 24. Other Examples: MultilingualVM’s • Dynamic Language Runtime (DLR). • Ruby, Python, ... on the .NET CLR. 24
  25. 25. Benefits •Optimize performance where it matters. •Optimize productivity, extensibility and agility everywhere else. Application Kernel of Components User Scripts Built-in Scripts 25
  26. 26. Disadvantages Application Kernel of Components User Scripts Built-in Scripts 26 •More complexity with 2+ languages (idioms, tools, ...).
  27. 27. An underutilized architecture! Application Kernel of Components User Scripts Built-in Scripts 27
  28. 28. Parting Thought... Cell phone makers are drowning in C++. (One reason the IPhone and Android are interesting.) 28
  29. 29. I don’t know what my code is doing. flickr.com/photos/dominic99 Specific problem #2
  30. 30. The intent of our code is lost in the noise.30
  31. 31. Symptoms •Business logic is obscure when I read the code. •The system breaks when we change it. •Translating requirements to code is error prone. 31
  32. 32. Solution #1 Write less code. Profound statement. 32
  33. 33. Less Code • Means problems are smaller: • Maintenance • Duplication (DRY) • Testing • Performance • etc. 33
  34. 34. How to Write Less Code • Root out duplication. • Use economical designs. • Functional vs. Object-Oriented? • Use economical languages. 34
  35. 35. Solution #2 Separate implementation details from business logic. 35
  36. 36. Domain Specific Languages Make the code read like “structured” domain prose. 36
  37. 37. Example DSLinternal { case extension when 100...200 callee = User.find_by_extension extension unless callee.busy? then dial callee else voicemail extension when 111 then join 111 when 888 play weather_report('Dallas, Texas') when 999 play %w(a-connect-charge-of 22 cents-per-minute will-apply) sleep 2.seconds play 'just-kidding-not-upset' check_voicemail end } Adhearsion = Ruby DSL + Asterisk + Jabber/XMPP + ... 37
  38. 38. DSL Advantages • Code looks like domain prose: • Is easier to understand by everyone, • Is easier to align with the requirements, • Is more succinct. 38
  39. 39. DSL Disadvantages • DSLs are hard to design, test and debug. • Some people are bad API designers. 39
  40. 40. Brueghel the Elder A DSL Tower of Babel? 40
  41. 41. Parting Thought... Perfection is achieved, not when there is nothing left to add, but when there is nothing left to remove. -- Antoine de Saint-Exupery 41
  42. 42. Parting Thought #2... Everything should be made as simple as possible, but not simpler. -- Albert Einstein 42
  43. 43. Corollary: Entia non sunt multiplicanda praeter necessitatem. -- Occam’s Razor 43
  44. 44. Corollary: All other things being equal, the simplest solution is the best. -- Occam’s Razor 44
  45. 45. We have code duplication everywhere. Specific problem #3 deanwampler
  46. 46. Symptoms • Persistence logic is embedded in every “domain” class. • Error handling and logging is inconsistent. Cross-Cutting Concerns. 46
  47. 47. Solution Aspect-Oriented Programming 47
  48. 48. Removing Duplication • In order, use: • Object or functional decomposition. • DSLs. • Aspects. 48
  49. 49. An Example... 49
  50. 50. class BankAccount attr_reader :balance def credit(amount) @balance += amount end def debit(amount) @balance -= amount end … end Clean Code 50
  51. 51. But, real applications need: def BankAccount attr_reader :balance def credit(amount) ... end def debit(amount) ... end end Transactions Persistence Security 51
  52. 52. def credit(amount) raise “…” if unauthorized() save_balance = @balance begin begin_transaction() @balance += amount persist_balance(@balance) … So credit becomes… 52
  53. 53. … rescue => error log(error) @balance = saved_balance ensure end_transaction() end end 53
  54. 54. We’re mixing multiple domains, Transactions Persistence Security with fine-grained intersections. “Problem Domain” “tangled” code “scattered” logic 54
  55. 55. Objects alone don’t prevent tangling. 55
  56. 56. Aspect-Oriented Programming: restore modularity for cross-cutting concerns. 56
  57. 57. Aspects restore modularity by encapsulating the intersections. Transactions Persistence Security Transaction Aspect Persistence Aspect Security Aspect 57
  58. 58. If you have used the Spring Framework, you have used aspects. 58
  59. 59. • Ruby • Aquarium • Facets • AspectR Aspect-Oriented Tools • Java • AspectJ • Spring AOP • JBoss AOP shameless plug 59
  60. 60. I would like to write… Before returning the balance, read the current value from the database. Before accessing the BankAccount, authenticate and authorize the user. After setting the balance, write the current value to the database. 60
  61. 61. I would like to write… Before returning the balance, read the current value from the database. Before accessing the BankAccount, authenticate and authorize the user. After setting the balance, write the current value to the database. 61
  62. 62. require ‘aquarium’ class BankAccount … after :writing => :balance do |context, account, *args| persist_balance account end … reopen class add new behavior Aquarium aquarium.rubyforge.org62
  63. 63. def credit(amount) @balance += amount end Back to clean code 63
  64. 64. Parting Thought... Metaprogramming can be used for some aspect-like functionality. DSLs can solve some cross-cutting concerns. (We’ll come back to that.) 64
  65. 65. Specific problem #4 flickr.com/photos/wolfro54 Our service must be available 24x7 and highly scalable.
  66. 66. Symptoms • Only one of our developers really knows how to write thread-safe code. • The system freezes every few weeks or so. 66
  67. 67. Solution Functional Programming 67
  68. 68. Functional Programming •Works like mathematical functions. Fibonacci Numbers: F(n) = F(n-1) + F(n-2) where: F(1) = 1 and F(2) = 1 68
  69. 69. Functional Programming • Variables are assigned once. • Functions are side-effect free. • They don’t alter state. y = sin(x) 69
  70. 70. Functional Programming Makes Concurrency Easier • Nothing to synchronize. • Hence no locks, semaphores, mutexes... 70
  71. 71. Which fits your needs? Object Oriented 71 Account deposit(...) withdraw(...) CheckingAccount deposit(...) withdraw(...) SavingsAccount deposit(...) withdraw(...) ?? deposit(...) withdraw(...)
  72. 72. list map fold/ reduce filter Which fits your needs? Functional 72
  73. 73. flickr.com/photos/deanwampler What if you’re doing cloud computing? 73 deanwampler Is it object-oriented or functional?
  74. 74. FP Code is declarative rather than imperative. F(n) = F(n-1) + F(n-2) where: F(1) = 1 and F(2) = 1 74
  75. 75. … and so are DSLs. class Customer < ActiveRecord::Base has_many :accounts validates_uniqueness_of :name, :on => create, :message => ‘Evil twin!’ end 75
  76. 76. A Few Functional Languages 76
  77. 77. Erlang • Ericsson Functional Language. • For distributed, reliable, soft real-time, highly concurrent systems. • Used in telecom switches. • 9-9’s reliability for AXD301 switch. 77
  78. 78. Erlang • No mutable variables and side effects. • All IPC is optimized message passing. • Very lightweight and fast processes. • Lighter than most OS threads. • Let it fail philosophy. 78
  79. 79. Scala • Hybrid: object and functional. • Targets the JVM and .NET. • “Endorsed” by James Gosling at JavaOne. • Used at Twitter, Linkedin, ... • Could be the most popular replacement for Java. 79
  80. 80. Clojure • Functional, with principled support for mutability. • Targets the JVM and .NET. • Best buzz? • Too many good ideas to name here... 80
  81. 81. Functional Languages in Production • Erlang • CouchDB • GitHub • Jabber/XMPP server ejabberd. • Amazon’s Simple DB. 81
  82. 82. Functional Languages in Production • OCaml • Jane Street Capital • Scala • Twitter • LinkedIn 82
  83. 83. Parting Thought... Is a hybrid object-functional language better than using an object language with a functional language?? e.g., Scala vs. Java + Erlang?? 83
  84. 84. Polyglot and Poly-paradigm Programming (PPP) for Better Agility Recap: 84
  85. 85. Disadvantages of PPP • N tool chains, languages, libraries, “ecosystems”, ... • Impedance mismatch between tools. • Different meta-models. • Overhead of calls between languages. 85
  86. 86. Advantages of PPP • Can use the best tool for a particular job. • Can minimize the amount of code required. • Can keep code closer to the domain. • Encourages thinking about architectures. • E.g., decoupling between “components”. 86
  87. 87. Everything old is new again. • Functional Programming Comes of Age. • Dr. Dobbs, 1994 • Scripting: Higher Level Programming for the 21st Century. • IEEE Computer, 1998 • In Praise of Scripting: Real Programming Pragmatism. • IEEE Computer, 2008
  88. 88. Why go mainstream now? •Rapidly increasing pace of development, ➔ Scripting (dynamic languages), DSLs. •Pervasive concurrency (e.g., Multicore CPUs) ➔ Functional programming. •Cross-cutting concerns ➔ Aspect-oriented programming. 88
  89. 89. Common Themes • Less code is more. • Keep the code close to the domain: DSLs. • Be declarative rather than imperative. • Minimize side effects and mutable data. 89
  90. 90. ThankYou! • dean@deanwampler.com • Watch for the IEEE Software special issue, Sept/Oct 2010. • polyglotprogramming.com 90

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