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  1. 1. Yet  another  Javascript  transpiler Iván  –  DrSlump  –  Montes @drslump  -­‐  -­‐, November 27, 12
  2. 2. Javascript  as  Virtual  MachineTuesday, November 27, 12
  3. 3. JS is the x86 of the web. The point is JS is about as low as we can go. But it also has higher-level facilities. Brendan  Eich JavaScript’s  creatorTuesday, November 27, 12
  4. 4. JavaScript is the VM of the web. We had always thought that Java’s JVM would be the VM of the web, but it turns out that it’s JavaScript. Douglas  Crockford JavaScript  evangelistTuesday, November 27, 12
  5. 5. The JavaScript weve got now is the assembly language of the client-side. We cant easily change it, but we have to start building better tools on top of it. Jonnycat Y  Combinator  userTuesday, November 27, 12
  6. 6. A  Popular  TrendTuesday, November 27, 12
  7. 7. grade = (student) -> if student.excellentWork "A+" else if student.okayStuff if student.triedHard then "B" else "B-" else "C" eldest = if 24 > 21 then "Liz" else "Ike" Open  source  project  with  a  huge  community Syntax  sugar,  more  a  pre-­‐processor  than  a   compiler Focused  on  having  a  very  concise  syntaxTuesday, November 27, 12
  8. 8. /**  * A shape.  * @interface  */ function Shape() {}; Shape.prototype.draw = function() {}; /**  * @constructor  * @implements {Shape}  */ function Square() {}; Square.prototype.draw = function() {   ... }; Backed  by  Google Annotated  Javascript  code More  a  staOc  analysis  tool  than  a  compilerTuesday, November 27, 12
  9. 9. interface Person { firstname: string; lastname: string; } function greeter(person : Person) { return "Hello, " + person.firstname + " " + person.lastname; } var user = {firstname: "Jane", lastname: "User"}; document.body.innerHTML = greeter(user); Backed  by  MicrosoP Type  extensions  to  JavaScript  syntax Focused  on  being  IDE  friendlyTuesday, November 27, 12
  10. 10. Why  so  many? • Javascript  syntax  is  geRng  dated  (Harmony  in  the  works   to  somehow  remedy  that) • Browser  war  has  focused  on  Javascript  engines,  huge   performance  boost  in  latest  years. • Programmers  with  many  different  backgrounds  using   Javascript  to  develop/deploy  complex  products. • Much  improved  debugging  tools  (Firebug,  SourceMaps,   OpOmizers,  …) • User  friendly  write-­‐compile-­‐test  workflows    Tuesday, November 27, 12
  11. 11. Won’t  Harmony  save  JavaScript? • The  standard  is  finally  coming  along  but  not  expected  to   be  finished  unOl  mid  2013.  Browser  vendors  are  not  too   far  from  having  a  working  implementaOon  though. • The  browser  market  is  hugely  fragmented,  mobile  devices   will  probably  held  back  early  adopOon  this  Ome,  although   we  will  conOnue  to  blame  MicrosoP  :-­‐) • Harmony  is  being  driven  to  be  highly  performant  on   current  engines  not  that  much  on  improving  developers   performance. • Harmony  will  be  a  good  step  forward  but  it  won’t  render   fuOle  the  JavaScript  as  Virtual  Machine  approach.Tuesday, November 27, 12
  12. 12. The  Boo  LanguageTuesday, November 27, 12
  13. 13. Boo is an object oriented statically typed programming language ... with a python inspired syntax and a special focus on language and compiler extensibility. Rodrigo  B.  De  Oliveira Boo’s  creatorTuesday, November 27, 12
  14. 14. import System class Person: public name as string public age as int def constructor(name as string): .name = name age = 0 def birthday(p as Person): p.age += 1 # Create an instance me = Person(DrSlump, age: 32) birthday(me) print "$( celebrated his $(me.age) birthday"Tuesday, November 27, 12
  15. 15. Readable  and  expressive  syntax Python  inspired DSL  oriented StaOcally  typed Type  inference Duck  typing Extensible Macros  and  Meta  methods  (AST  manipulaOon) Open  compiler  design  (Pipelines)Tuesday, November 27, 12
  16. 16. Language  Features .Net  Type  System  (classes,  value  types,  interfaces,  ...) Slicing  syntax,  Variadic  arguments,  IniOalizers FuncOons  are  first  class  ciOzens Closures Events,  Generators,  Expression  modifiers Method  and  Operators  OverloadingTuesday, November 27, 12
  17. 17. Extensibility  and  Meta  programming SyntacOc  Macros  and  Afributes Meta  methods  (macros  aPer  type  resoluOon) Pafern  Matching Custom  pipelines Compiler  as  a  serviceTuesday, November 27, 12
  18. 18. BooJs boo·jay·es /bʊ ˈdʒeɪ ɛs/Tuesday, November 27, 12
  19. 19. Why  did  you  do  it? More  bang  for  the  buck If  we  are  going  to  require  a  compilaOon  workflow,  lets   have  a  really  powerful  compiler,  not  just  syntacOc  sugar. An  almost  perfect  type  system A  staOcally  typed  language  with  the  look  and  feel  of  a   scripOng  language  is  a  great  combinaOon,  specially  for   medium  to  large  code  bases.  It’s  just  one  small  step  short   from  latent  typing,  which  I  hope  to  support  in  the  future. It  is  FUN! Programming  is  fun  ergo  programming  compilers  is  twice   as  fun!Tuesday, November 27, 12
  20. 20. Comparison  with  Javascript Boo JavaScript First-­‐class  funcEons  ✓  ✓ FuncEon  expressions  ✓  ✓ Closures  ✓  ✓ Scope Lexical  (funcOon  and  types) Lexical  (funcOon) Type  system StaOc  and  Dynamic  (strong) Dynamic  (weak) Variadic  funcEons  ✓  ✓  (via  arguments) Inheritance Class/Type  based Prototypal Generators  ✓ ✘ List  comprehensions  ✓ ✘ Iterators  ✓ ✘ ProperEes  ✓ ✘ Destructuring  ✓ ✘ Method  overloading  ✓ ✘ Operator  overloading  ✓ ✘ Macros  ✓ ✘ PaLern  Matching  ✓ ✘Tuesday, November 27, 12
  21. 21. ImplementaOon Leverages  Boo’s  open  compiler  design Implemented  using  the  Boo  language Runs  on  .Net  4.0  and  Mono  2.1.x Over  700  unit  tests,  automated  with  Travis-­‐CI Generates  a  Mozilla  AST,  prefy  printed  to  JS  1.5 SourceMaps  support   JS  type  system  and  runOme  (no  .NET  emulaOon!) Lightweight  runOme  library  (≈4kb  gzipped)Tuesday, November 27, 12
  22. 22. ApplicaOon  structure Each  file  is  a  Module Each  Module  has  a  single  Namespace Modules  are  organized  in  Assemblies Only  one  of  the  modules  can  be  the  entry  point External  Namespaces  and  Types  can  be  imported Each  assembly  generates  an  output  Javascript  file An  AMD  style  loader  is  used  to  resolve  dependenciesTuesday, November 27, 12
  23. 23. Using  exisOng  JavaScript  code Macros  and  afributes  to  model  external  Javascript Standard  APIs  like  the  DOM/jQuery  are  provided Support  for  prototypal  and  Module  Pafern  styles Extern  type  definiOons  do  not  generate  any  code `backOck  quoted  code`  is  embedded  unmodified Global  macro  to  access  exisOng  symbols Duck  typing  allows  to  use  pracOcally  everything!Tuesday, November 27, 12
  24. 24. Code  exampleTuesday, November 27, 12
  25. 25. Tuesday, November 27, 12
  26. 26. The limits of my language are the limits of my world. Ludwig  Wifgenstein Philosopher  (1889-­‐1951)Tuesday, November 27, 12
  27. 27. Related  material BooJs  project  page Boo  websiteTuesday, November 27, 12