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JRuby, Not Just For Hard-Headed Pragmatists Anymore
The document discusses a presentation on compiling using JRuby, focusing on the theoretical aspects of compiler creation rather than pragmatic applications. The talk outlines the process of writing a compiler for a fictional language, 'thnad', covering elements like parsing integers, function calls, conditionals, and function definitions, alongside tools like Parslet and Bitescript. It aims to engage the audience with live coding and a unique approach compared to other presentations at the conference.
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JRuby, Not Just For Hard-Headed Pragmatists Anymore
- 1. JRUBY, NOT JUSTFOR HARD- HEADED PRAGMATISTS ANYMORE IAN DEES • @UNDEES WHISKEY- CONF 2011 ✹ ALSO JR UBY Hi, I’m Ian. Hope everyone’s having a great WhiskyConf. I hear we’ll have some JRuby material at this conference as well. ;-) http://www.flickr.com/photos/etnobofin/3786071796
- 2. Write a Compiler MostJRuby talks are pragmatic: either a case study of how JRuby helped a project, or a specific library that developers can use. This talk will be more theoretical. We’ll use JRuby as a vehicle to explore an area of computer science; namely, writing a compiler.
- 3. The Three Paths Abstraction compilers Time Depending on your path through computer science, you may have encountered the topic already.
- 4. Abstraction compilers xor eax, eax e- Time If, like me, you grew up on the hardware path, a compiler is the next logical step beyond learning programming languages.
- 5. logic λx.x grammars Abstraction compilers xor eax, eax e- Time If you took the software path and learned the theory of computation first, then compilers are a practical application of those ideas.
- 6. logic λx.x grammars Abstraction compilers xor eax, eax e- Time If you took the self-made path, you may or may not have encountered compilers by this point on your journey. Either way, I hope the tools we talk about today pique your interest.
- 7. The Plan ✓Stay up late drinking whisky ✓Wear the T-shirt of the band that’s playing ✓Choose the wrong topic ✓Go at a pace that’s awkward for everyone ✓Code live on stage The plan for this talk is to show up tired, wear a JRubyConf t-shirt (this is like showing up at a concert wearing the t-shirt of the band that’s playing), choose a topic and pace different from all the other talks, and introduce an element of uncertainty by coding on stage. (If you’re reading this, I’ll show you GitHub commits instead.)
- 8. This might bea train wreck, but train wrecks can be entertaining as long as they’re toy trains. http://www.flickr.com/photos/cianginty/3148870954
- 9. The Tools • Parslet http://kschiess.github.com/parslet • BiteScript https://github.com/headius/bitescript • Gritty https://github.com/undees/gritty • Graph http://rubygems.org/gems/graph • JRuby! The first two tools are the ones we’ll use to write the compiler. The next two are the ones I used to draw the pictures on the subsequent slides.
- 10. The Language The languagewe’re going to be writing a compiler for is an extremely simple one.
- 11. Thnad (thank you, Dr. Seuss!) Most of the real letters of the alphabet are already used for programming languages (C, D, J, K, R, etc.). So we’ll use the fictional letter “Thnad,” which comes to us from Dr. Seuss.
- 12. function factorial(n) { if (eq(n, 1)) { 1 } else { times(n, factorial(minus(n, 1))) } } print(factorial(4)) Here’s the Thnad program we’d eventually like to compile. It has integers, function calls, conditionals, and function definitions—and that’s about it.
- 13. 1. Integers One bigstep is to write a compiler top to bottom that parses an integer and outputs a working Java .class file.
- 14. 42 First, we’re goingto write code that parses the text “42” into a Ruby hash representing the tree on the right.
- 15. Following Along • Test → test_parser.rb • Code → parser.rb Slides like this one will contain a link to the tests, code, or full examples for the steps we’ve just been over.
- 16. Next, we’re goingto transform that Ruby hash (which isn’t as useful by itself) into a custom Ruby class that will eventually be able to output Java bytecode.
- 17. • Test →test_transform.rb • Code → transform.rb • Full Example
- 18. 2. Function Calls Now,let’s add the ability to compile function calls.
- 19. foo We need tobe able to parse identifiers; we’ll use these for function and parameter names.
- 20. As we didwith integers, we want to transform the first hash representation into a more specific Ruby object.
- 21. (42, foo) Next, we’llparse an argument list, which is a set of parentheses containing integers and parameter names.
- 22. We’ll need codeto transform that into an array of the Ruby objects we’ve already defined.
- 23. baz(42, foo) Now, we’refinally ready to parse a function call...
- 24. ...and transform itinto a Ruby object that will be able to emit bytecode.
- 25.
- 26. 3. Conditionals The nextbig piece of our compiler is the conditional expression.
- 27. if (0) { 42 } else { 667 } Here’s the kind of conditional statement we’d like to be able to parse. The “else” clause is mandatory (I hope Zed Shaw will approve).
- 28. Paradoxically, the morecomplicated the expression we parse, the more our tree of custom Ruby classes resembles the Ruby hash we started with.
- 29.
- 30. 4. Function Definitions Thelast piece we need for our factorial Thnad program is the ability to compile function definitions.
- 31. function foo(x) { 5 } A function definition is the keyword “function” followed by a list of parameters in parentheses, then a computation between braces.
- 32. And here’s theresulting tree of Ruby objects.
- 33.
- 34. Marc-André Cournoyer Marc-André Cournoyer’sbook on creating your own programming language was helpful during this process as a way of “checking my answers” (just like checking your answers to today’s crossword puzzle by looking in tomorrow’s paper).
- 35. Code https://github.com/undees/thnad The full compiler, complete with bytecode generation, is available here.
- 36. For more aboutJRuby (which made this whole exercise possible in half an hour), see our book at http://pragprog.com/titles/jruby.