1. Bringing Reflection to Life with First-Class Interpreters
Toon Verwaest
Camillo Bruni
David Gurtner
Adrian Lienhard
Oscar Nierstrasz
Software Composition Group
University of Bern
Switzerland

2. debugging is hard

3. System.out.println

4. developing debuggers is even harder

5. Object-Flow Debugger
Lienhard '07

6. modifications to the Virtual Machine

8. What if we could build a specialized debugger in just a few hours?

9. implement debuggers in the language itself in terms of the source code

10. Debugger interpret: [ Person new ]

11. Debugger interpret: [ Person new ] reflection

12. recursive AST visitor garbage collection object model Interpreter
environment
visitAssign:
visitBlock:
visitClass:
visitConstant:
visitSelf:
visitSend:
visitSuper:
visitVariable:
...
interpret:
send:to:class:
classOf:
invokeMethod:
recursive AST visitor
garbage collection
object model

13. recursive AST visitor garbage collection object model Interpreter
environment
interpret:
send:to:class:
classOf:
invokeMethod:
...
recursive AST visitor
garbage collection
object model
Debugger
send:to:class:
shell

14. send: message to: receiver: class: class self print:
receiver class name,'>>', message.
self shell.
^ super
send: message
to: receiver
class: class
Interpreter
environment
interpret:
send:to:class:
classOf:
invokeMethod:
...
Debugger
send:to:class:
shell

15. AliasInterpreter interpret: [
person := Person new.
person name: 'John'.
person name: 'Doe'.
person ]

32. interpretMethod: method | result |
Interpreter
environment
interpret:
send:to:class:
classOf:
interpretMethod:
...
interpretMethod: method
| result |
result := super interpretMethod: method.
^ (ReturnAlias alias: result)
environment: environment
AliasInterpreter
classOf:
interpretMethod:
...

33. AliasInterpreter interpret: [
person := Person new.
person name: 'John'.
person name: 'Doe'.
person ]

34. Pinocchio Metacircular
Performance (fib)
2.5x slower than Squeak
2x slower than Ruby 1.9
1.3x faster than Python 2.6.4
6x faster than Ruby 1.8
160x slower than Pinocchio
Pinocchio
Metacircular

35. Pinocchio Metacircular Ruby 1.8 Performance (fib)
2.5x slower than Squeak
2x slower than Ruby 1.9
1.3x faster than Python 2.6.4
6x faster than Ruby 1.8
160x slower than Pinocchio
Pinocchio
Metacircular
Ruby 1.8
163x slower than Java 1.6

36. Future work debuggers as recursive AST visitors
extensible using OO techniques
implemented practical debuggers
Future work
performance is not addressed yet

37. Future work http://scg.unibe.ch/pinocchio
debuggers as recursive AST visitors
extensible using OO techniques
implemented practical debuggers
Future work
performance is not addressed yet