1. Distributed Meta- Programming Rui Shi, Chiyan Chen and Hongwei Xi Boston University

2. Outline MP vs. DMP Typeful Code Representation The Language dist The Language + dist Discussion and Conclusion

3. Meta-Programming (define (run code) (eval code nil)) (define (power n x) (if (= n 0) 1 `(*,x,(power (- n 1) x)))) ;;; (power 2 ‘x) yields (* x (* x 1)) (define square (run `(lambda (x),(power 2 ‘x)))) ;;; (power 3 ‘y) yields (* y (* y (* y 1))) (define cube (run `(lambda (y),(power 3 ‘y))))

4. Distributed Meta-Programming Cod e Run-time code generation Distributed execution

5. Outline MP vs. DMP Typeful Code Representation The Language dist The Language + dist Discussion and Conclusion

6. `(“abc” + 10) (ill-typed) `(( y.x) 10) (open code) Un-typed Code Representation No guarantee on the safety of generated code.  Code can be syntactically ill-formed or ill-typed, which lead to run-time errors when executed at remote sites.  Issues of locality and heterogeneity of resources Different sites may have different resources and thus likely to provide different services. f : (Int ! Int)@L L `(f 100) L’

7. Typeful Code Representation (T.C.R) The types of object programs can be reflected in the types of meta programs  E.g. code of type h , T i represents an object program of type T under the type environment . The type of the code also reflects where it should be sent for execution.  E.g. code of type h L, , T i can be sent to location L for execution. The compiler can statically guarantee that only well-typed code can be constructed at run-time and sent to proper locations for execution.

8. Outline MP vs. DMP Typeful Code Representation The Language dist The Language + dist Discussion and Conclusion

9. The Language dist

10. First-Order Code Constructors For example, the term x. y. y (x) can be represented as: which can be of type (with static variables properly instantiated) Lam (Lam (App (One) (Shi (One)))) 8. h, , int ! (int ! int) ! int i

11. Some Primitive Functions

12. Constant Messages Constant messages refer to the messages which can be interpreted at all sites. Example: perform addition of two integers at remote site

13. An Example in dist f : (Int ! Int)@L L `(f 100) rget int (L, rexec (L, App (Lift (n2m f)), Lift 100) )) of type h L, , int i

14. Outline MP vs. DMP Typeful Code Representation The Language dist The Language + dist Discussion and Conclusion

15. The Language + dist We extend dist to + dist with some language constructs adopted from meta-programming (supported in Scheme and MetaML):  `(e) for the code representation of e  ^(e) for spliceing the code e into some context  %(¢) is a shorthand for ^(Lift(¢))

16. An Example in Concrete Syntax of + dist typedef CodeType (L: loc) = int) -> int> fun rZeroFind2{L:loc} (L:loc(L)) (n: (int -> int) @ L) : int = let val zeroFindCode : CodeType (L) = `(lam f => (fix aux i => if f (i) = 0 then i else aux (i+1)) 0) in rexecInt (L, `(^zeroFindCode %(n2m n))) end

17. Outline MP vs. DMP Typeful Code Representation The Language dist The Language + dist Discussion and Conclusion

18. Discussion We have a transformation scheme from + dist to dist to justify the soundness of + dist. We have a process to elaborate programs (partial type inference) in the concrete syntax to the formal syntax of + dist DMP is implemented as a part of ATS (Applied Type System) framework.

19. Conclusion A simple and general approach to support typed mobile computing. Combines meta-programming with distributed programming in a coherent manner. In future, we are planning to study issues such as exception handling and distributed garbage collection in this context.

20. Thank You!