A Direct Semantics of Declarative Disambiguation Rules
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This document discusses research into providing a direct semantics for declarative disambiguation of expression grammars. It aims to define what disambiguation rules mean, ensure they are safe and complete, and provide an effective implementation strategy. The document outlines key research questions around the meaning, safety, completeness and coverage of disambiguation rules. It also presents contributions around using subtree exclusion patterns to define safe and complete disambiguation for classes of expression grammars, and implementing this in SDF3.
A Direct Semantics of Declarative Disambiguation Rules
- 1. LUIS EDUARDO S. AMORIM (Delft University of Technology) TIMOTHE ́E HAUDEBOURG (ENS Rennes) MICHAEL J. STEINDORFER (Delft University of Technology) EELCO VISSER (Delft University of Technology) TU Delft March 2019 A Direct Semantics for Declarative Disambiguation of Expression Grammars
- 2. What is the meaning of associativity and priority declarations? !2
- 3. !3 Major revision of TOPLAS submission Work in progress 68 pages
- 4. What is the meaning of a set of disambiguation rules for a grammar? - What are the parse trees associated with sentences in the language of the disambiguated grammar? - independent of particular implementation strategy? Is a set of disambiguation rules safe? - Do the disambiguation rules preserve the language of the grammar they disambiguate? - Is it necessary for disambiguation rules to be safe, or can rules exclude sentences? Is a set of disambiguation rules complete? - Do the rules identify at most one parse tree for each sentence in the language? - Not obvious: ambiguity of CFGs is undecidable What is the coverage of disambiguation rules? - What classes of ambiguity do the rules solve? What is an effective implementation strategy for disambiguation rules? What is the notational overhead of disambiguation rules? - More effective than an encoding in the grammar? !4 Research Questions
- 5. Expression grammars - Sub-classes of CFGs with decidable ambiguity - Extraction of embedded expression grammars Harmless overlap - Avoid inherent ambiguities Subtree exclusion patterns - Deep priority conflict patterns Safe and complete - Preserve language and solve all ambiguities - Proof: induction on trees under subtree exclusion Implementation in SDF3 - Transformation to contextual grammars - Data-dependent parsing Evaluation on 5 programming languages !5 Contributions
- 6. This Talk !6
- 7. !7
- 9. Grammars, Well-Formed Trees, Languages !9
- 10. Parsing !10
- 11. Derivations !11 Lemma 2.5. A parse tree directly corresponds to a derivation, modulo the order in which productions are applied.
- 12. Parse Tree to Abstract Syntax Tree !12
- 13. Tree Patterns and Pattern Matching !13
- 14. Tree Patterns and Pattern Matching: Example !14
- 15. Ambiguity !15
- 19. Trees under Subtree Exclusion !19
- 23. Classes of Expression Grammars !23 Basic Distfix Indirectly recursive
- 29. Subtree Exclusion is Safe !29
- 30. Subtree Exclusion is Safe !30
- 31. Subtree Exclusion is Safe !31
- 32. Subtree Exclusion is Safe !32
- 33. Total Set of Disambiguation Rules !33
- 34. Subtree Exclusion is Complete !34
- 35. Subtree Exclusion is Complete !35
- 36. Subtree Exclusion is Complete !36
- 37. Subtree Exclusion is Complete !37
- 38. Subtree Exclusion is Complete !38
- 39. Disambiguation for Infix Expression is Safe and Complete !39
- 42. SDF2 Semantics is Unsafe for Prefix Expression Grammars !42
- 44. Safe Semantics for Shallow Conflicts !44
- 48. Rightmost Deep Priority Conflict Pattern !48
- 49. Etc. 49