Introducing Static Semantic Analysis to Templates Using JastAdd

1. Introducing Static Semantic Analysis to Templates Using JastAdd Jos Peeters

2. Goal Ambition • Improve the quality of code generators based on templates. Primary Research Question • Can static semantic checking be used in template-based code generators using off-the-shelf tooling? / name of department

3. Research Questions • Can JastAdd be coupled to Repleo? • Is the resulting coupling scalable? • How can static semantic checking be performed on templates? • How to deal with syntactic ambiguities? • How to implement this using JastAdd? / name of department

4. Research Questions • Tools • Repleo • JastAdd • Connection • Methodology • Placeholders • Static Semantic Checking • Syntactic Ambiguities • Implementing the Methodology • Conclusion / name of department

5. Tools • Repleo • Syntax-safe template engine • JastAdd • Java-based compiler compiler system • Object-oriented abstract syntax • Advanced attribute grammar features / name of department

6. Repleo • Templates • Architectural Pattern • Code with empty spaces and generative commands • Features • Guarantees syntax-safe output code • Provides meta-language for templates / name of department

7. Repleo / name of department

8. JastAdd • Features • Abstract Syntax • Parser Independent • Extended support Attribute Grammars • Aspect Oriented / name of department

9. JastAdd / name of department

10. Abstract syntax abstract BlockStmt; abstract Stmt: BlockStmt; AssignStmt : Stmt ::= Variable:Access Value:Exp; WhileStmt : Stmt ::= Condition:Exp Body:Stmt; abstract Exp; abstract Access:Exp; IntLiteral : Exp ::= <Value:String>; abstract Operator : Exp; abstract BinOperator : Operator ::= lhs:Exp rhs:Exp; PlusOp : BinOperator; / name of department

11. Attributes Properties as attributes • Synthesized • Inherited • Equations Also: • Rewrites • Circular attributes • Non-terminal attributes / name of department

12. Weaving Aspects aspect TypeAnalysis { synlazy TypeDecl Exp.type(); eq BinOperator.type() { if (getlhs().type().isSubtypeOf(getrhs().type()) || getrhs().type().isSubtypeOf(getlhs().type()) ) { if (getlhs().type().isUnknown() ) return getrhs().type(); return getlhs().type(); } return unknownDecl().type(); } eq IntLiteral.type() = intType(); } / name of department

13. Connection • Boolean Evaluator • Simple boolean expressions • Java 1.4 • Using JastAddJ / name of department

14. Connection / name of department

15. Connection JastAddJ Issues • No strict separation between checker and parser • Instantiation parts of checker • Rewriting during parse phase • Grammar differences between SDF and AST For placeholder a 1-to-1 transformation is required / name of department

16. Research Questions • Tools • Repleo • JastAdd • Connection • Methodology • Placeholders • Static Semantic Checking • Syntactic Ambiguities • Implementing the Methodology • Conclusion / name of department

17. Placeholders(1) What are placeholders? • Representation of empty space in code • Substitution or generative command • Properties defined by place of occurrence "<:" TreeQuery ":>" -> PlaceHolderSubstitution[[X]] / name of department

18. Placeholders(2) Substitution int <: x :>; Conditional <: if x == "true" then :> boolean b; <: else :> int i; <: fi :> / name of department

19. Placeholders (3) Iterative int i = 0; <: foreach $x in X do :> i = i + <: $x :>; <: od :> Match-Replace int i = 0; i = <: match X :> <: [$e,$t] = :> <: $e :> + <: $t :> <: [] = :> 0 <: end :>; / name of department

20. Static Semantic Checking • Target language • Type checking • Context related checks (f.i. duplicate declarations) • Placeholders language • Uniqueness meta-variables (i.e. $e) • Combination of both • Checking influence of placeholders on target language • “Bad Smells” / name of department

21. Bad Smells Not permitted • errors that are related to properties of placeholders <: foreach $x in X do :> int i; <: od :> Permitted • restrictions given only by the input data <: foreach $x in X do :> int <: $x :>; <: od :> / name of department

22. Syntactic Ambiguities • Occur when multiple production can be applied • Parsing problem • SGLR • Bad Smell publicclass A { <: a :> <: b :>(){} } / name of department

23. Disambiguation • Via Context • Use static semantic checker • Compare previous use of placeholders publicclass A { <: a :> i = 0; <: a :> <: b :>(){} } / name of department

24. Disambiguation • Using prioritization • Select the option containing the placeholder { int i; i = <: a :>; } / name of department

25. Research Questions • Tools • Repleo • JastAdd • Connection • Methodology • Placeholders • Static Semantic Checking • Syntactic Ambiguities • Implementing the Methodology • Conclusion / name of department

26. Implementing the Methodology PicoJava • Subset of Java • Originally an example of JastAdd Present • PicoJava language definition in JastAdd • Attributes to support checking • Static semantic checker • SDF definition Placeholders / name of department

27. Pipeline / name of department

28. Implementation Implemented as part of this project • SDF definition PicoJava • Traversal SGLR  JastAdd With JastAdd • Language definition placeholders • Extend attributes for the placeholders • Static semantic checker • Placeholders • Bad Smells • Ambiguity nodes • Disambiguation filter NB. JastAdd is Aspect-Oriented / name of department

29. template( { <: if x == $e then :> boolean i; i = <: match y :> <: [$e, $t] = :> <: $e :> + <: $t :> <: [] = :> 0 <: end :>; <: fi :> i = 0; } ) 1 2 3 4 5 6 7 8 9 10 11 12 Example - Template / name of department

30. Example – Output(1) --> Resolving ambiguities 6:21 Ambiguity found: Exp Ambiguity resolved using prioritization 6:32 Ambiguity found: Exp Ambiguity resolved using prioritization Done / name of department

31. Example – Output(2) --> Language Errors 10:2 : Can not assign to a variable of type boolean a value of type int --> Placeholder Errors 6:6 : duplicate declaration of meta-variables [$e] --> Placeholder Bad Smells 7:6 : inferred type of placeholder does not match the type of its declaration 10:2 : Variable i might not be declared, dependent on [x] --> List of PlaceHolders $e PhExp $unknown $unknown $t PhExp $unknown $unknown y PhMRExp $unknown int x PhIfBlockStmt $unknown $unknown / name of department

32. Conclusions Presented in this Thesis • Static Semantic Checks on Template • Use of off-the-shelf tools • Repleo • JastAdd Methodology • Multi-language approach • Ease-of-use of templates • Syntax-safe • Static Semantic Analysis / name of department

33. Questions / name of department