1 / 25

Grammar Variation in Compiler Design

Grammar Variation in Compiler Design. Carl Wu. Three topics. Syntax Grammar vs. AST Component(?)-based grammar Aspect-oriented grammar. Grammar vs. AST (I). How to automatically generate a tree from a grammar?. Grammar vs. AST (I). Stmt ::= Block | “if” Expr “then” Stmt

alice
Download Presentation

Grammar Variation in Compiler Design

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Grammar Variation in Compiler Design Carl Wu

  2. Three topics • Syntax Grammar vs. AST • Component(?)-based grammar • Aspect-oriented grammar

  3. Grammar vs. AST (I) How to automatically generate a tree from a grammar?

  4. Grammar vs. AST (I) Stmt ::= Block | “if” Expr “then” Stmt | IdUse “:=” Exp

  5. Grammar vs. AST (I) Stmt ::= Block | “if” Exp “then” Stmt | IdUse “:=” Exp JastAdd Specification (Tree) abstract Stmt; BlockStmt : Stmt ::= Block; IfStmt : Stmt ::= Exp Stmt; AssignStmt : Stmt ::= IdUse Exp;

  6. Grammar vs. AST (I) Restricted CFG Definition A ::= B C D √ => aggregation A ::= B | C | D √ => inheritance A ::= B C | D ×

  7. Grammar vs. AST (I) RCFG Specification Stmt :: Block | IfStmt | AssignStmt IfStmt :: “if” Exp “then” Stmt AssignStmt :: IdUse “:=” Exp

  8. Grammar vs. AST (II) Parse tree vs. IR tree

  9. Grammar vs. AST (II) • In an IDE, there are multiple visitors for the same source code (>12 !). • Different requirement for the tree structure: • Syntax vs. semantics • Immutable vs. transformable (optimization) • Parse tree vs. IR tree

  10. Grammar vs. AST (II) • Generate two tree structures from the same grammar! • One immutable, strong-typed, concrete parse tree – Read only! • One transferable, untyped, abstract IR tree – Read and write!

  11. Grammar vs. AST (II) IfStmt :: “if” Exp “then” Stmt Class ASTNode{ protected ASTNode[] children; } class IfStmt extends ASTNode{ final protected Token token_if, Exp exp, Token token_then, Stmt stmt; IfStmt(Token token_if, Exp exp, Token token_then, Stmt stmt){ // parse tree construction this.token_if = token_if; this.exp = exp; this.token_then = token_then; this.stmt = stmt; // IR tree construction children[0] = exp; children[1] = stmt; } }

  12. Component(?)-based grammar

  13. Component vs. module • What is the different between a component and a module? • What is a modularized grammar? • What is an ideal component-based grammar?

  14. Component vs. module Grammar Module Grammar Module Grammar Component Grammar Component Grammar Parser Parser Parser Modularized grammar Component-based grammar

  15. Benefits • Benefits from modularized grammar • Easy to read, write, change • Eliminate naming conflicts • Additional benefits brought from component-based grammar • Each component can be designed, developed and tested individually. • Any change to certain component does not require compiling all the other components. • Different type of grammars/parsing algorithms can be used for different component, e.g., one component can be LL, one can be LALR.

  16. Difficulty in designing component-based grammar • No clear guards between two components. • Switch the control to a new parser or stay in the same? • Suitable for embed languages, e.g., Jscript in Html • Not suitable for an integral language, e.g., Java • Two much coupling between two components. • Not just reuse the component as a whole, may also reuse the internal productions and symbols. • Not applicable for LR parsers, once the table is built, you can’t reuse the internal productions (no way to jump into a table).

  17. Ideal vs. reality

  18. Suggestions?

  19. Aspect-oriented grammar

  20. Aspect-oriented grammar • Join-point: grammar patterns that crosscut multiple productions • Punctuations, identifiers, modifiers…

  21. Example • ";“ appears 25 times in one of the Java grammars • “.” appears 74 times in one of the Cobol grammars • Every one of them should be carefully placed!

  22. <Sentence> ::= <Accept Stm> '.' | <Add Stm> '.' | <Add Stm Ex> <End-Add Opt> '.' | <Call Stm> '.' | <Call Stm Ex> <End-Call Opt> '.' | <Close Stm> '.' | <Compute Stm> '.' | <Compute Stm Ex> <End-Compute Opt> '.' | <Display Stm> '.' | <Divide Stm> '.' | <Divide Stm Ex> <End-Divide Opt> '.' | <Evaluate Stm> <End-Evaluate Opt> '.' | <If Stm> <End-If Opt>'.' | <Move Stm> '.' | <Move Stm Ex> <End-Move Opt> '.' | <Multiply Stm>'.' | <Multiply Stm Ex> <End-Multiply Opt> '.' | <Open Stm> '.' | <Perform Stm> '.' | <Perform Stm Ex> <End-Perform Opt> '.' | <Read Stm> '.' | <Read Stm Ex> <End-Read Opt> '.' | <Release Stm> '.' | <Rewrite Stm> '.' | <Rewrite Stm Ex> <End-Rewrite Opt> '.' | <Set Stm> '.' | <Start Stm> '.' | <Start Stm Ex> <End-Start Opt> '.' | <String Stm> '.' | <String Stm Ex> <End-String Opt> '.' | <Subtract Stm>'.' | <Subtract Stm Ex> <End-Substract Opt> '.' | <Write Stm> '.' | <Write Stm Ex> <End-Write Opt> '.' | <Unstring Stm>'.' | <Unstring Stm Ex> <End-Unstring Opt> '.' | <Misc Stm> '.' pointcut PreDot(): <Sentence>; after PreDot(): ‘.'

  23. Another example pointcut Content(): … … before Content(): “(”; after Content(): “)”; Guarantee they match!

  24. Grammar weaving Base Grammar Grammar Aspect Result grammar Parser

  25. What do you think?

More Related