LCA2011 miniconf presentation on compiler construction for the JVM.

1. Compiler Construction for the JVM Tom Lee [email_address] Senior Consultant Shine Technologies http://www.shinetech.com

3. Why target the JVM?

4. Compiler Construction 101

5. “Hello World”

6. Scala's Parser Combinators

7. “Hello World” in AST form

8. Representing ASTs in Scala

9. Compiling ASTs with BCEL

10. A Small Proof of Concept

13. Compilation of ASTs within Python in 2.6

18. Compiler Construction 101

19. “Hello World” puts(“Hello World”);

20. “Hello World” (cont.) puts ( “Hello World” ) ;

21. “Hello World” (cont.) putsStmt -> “puts” “(“ str “)” “;” str -> STR STR -> regex(“[^”]*”)

22. “Hello World” (cont.) call -> name “(“ str “)” “;” name -> ID str -> STR ID -> regex([a-zA-Z_][a-zA-Z_0-9]*) STR -> regex(“[^”]*”)

23. “Hello World” (cont.) stmt -> expr “;” expr -> str | call call -> name “(“ args? “)” args -> expr ( “,” expr)* str -> STR name -> ID STR -> regex(“[^”]*”) ID -> regex([a-zA-Z_][a-zA-Z_0-9]*) By deriving these grammars, we make it easy to reproduce them in Scala. How?

26. Scala's Parser Combinators (cont.) expr -> str | call call -> name “(“ args? “)” “;” ... Grammar def expr = str | call def call = name ~ (“(“ ~> args? <~ “)”) “;” ... Scala

27. “Hello World” in AST form

28. “Hello World” in AST form (cont.) o_O For the sake of simplicity, we'll pretend all our programs consist of a single expression...

30. Trait for expressions

31. Trait for statements

32. Case classes for everything else

33. Representing ASTs in Scala (cont.) trait AST {} // trait Stmt extends AST {} trait Expr extends AST {} case class Call(name : Name, args : List[Expr]) extends Expr case class Name(id : String) extends Expr case class Str(value : String) extends Expr

35. Generate logically equivalent bytecode

39. Convert it to its parser combinator equivalent

40. Act upon parse results to construct an AST

41. Generate logically equivalent JVM bytecode