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Typed AG

Typed AG. Alexey Rodriquez Y Faridah Liduan Type Systems Project 26 Jun 2003. Introduction. Goals. Produce a well-typed AG file Detect type errors of semantic functions early in the AG stage Do type checking and type inferencing using: AG type annotations

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Typed AG

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  1. Typed AG Alexey Rodriquez Y Faridah Liduan Type Systems Project 26 Jun 2003

  2. Introduction

  3. Goals • Produce a well-typed AG file • Detect type errors of semantic functions early in the AG stage • Do type checking and type inferencing using: • AG type annotations • Types of haskell source fragment • Local attributes definitions

  4. Why Typed AG? • Well typed AG => well typed haskell program • Typed errors are given in terms of the AG source

  5. AG Type Errors in Terms of Haskell Source

  6. How to Merge AG and UHC

  7. Embedding AG to UHC (Attribute Haskell) • Advantages: • Haskell is extended with attribute grammar • Make use features of haskell interpreter and haskell compiler • AG will have a module system if it is properly done • Disadvantages: • Utterly Complex • Proper language design vs gluing

  8. Embedding UHC to AG (Typed AG) • Advantages: • Easier to implement • Disadvantages: • Still a two-step process • Improvements in the UHC do not apply to Typed AG

  9. Our Choice • Implement Typed AG

  10. Typing Semantic Functions

  11. AG Data and Semantic Function Definition

  12. AG Generated Semantic Function

  13. How to Type Check Semantic Functions

  14. How to Type Check Semantic Functions (cont~)

  15. Simple Subset (no local attributes)

  16. Implementation of Typed AG

  17. AG Example

  18. AG Data Flow Diagram

  19. Implementation Choice

  20. Other implementation choice?

  21. Type Inference of Local Attributes

  22. Implementation Options • Simple Dependency Analysis Type inference over local variables in the order determined by the analysis • Constraint: no cycles (cycle = incorrect result) • Use bindgroup • Put all local attributes in a bindgroup and do type inferencing. • Disadvantages: no polymorphic local attributes

  23. Implementation Options (cont~) • Use HC Constructors Use semantic functions to type check local, synthesized, and inherited attributes. • Disadvantages: Error messages are not given in terms of original AG source.

  24. Implementation Issues

  25. AG + UHC • UHC copied to the AG repository. • Slight modification of existing Makefiles.

  26. Current State of Affairs • Our implementation can detect type errors in the embedded Haskell source fragments. • It can also detect type errors related to misuse of semantic functions. • Type errors are also detected in the RHS of the attribute rules.

  27. Missing features from UHC and our implementation • Type synonyms are not supported. • Types are not parsed. • Omission of local attributes (& patterns). • Typing of attribute expressions as a whole.

  28. Final Remarks • Typed AG guarantees well-typedness of generated Haskell source file. • A really useful implementation of Typed AG will need modules and full Haskell.

  29. Q & A

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