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Lecture 5: Syntax Analysis

The University of North Carolina at Chapel Hill. Lecture 5: Syntax Analysis. COMP 144 Programming Language Concepts Spring 2002. Felix Hernandez-Campos Jan 18. Source Code. Interpre- tation. Target Code. Review: Compilation/Interpretation. Compiler or Interpreter

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Lecture 5: Syntax Analysis

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  1. The University of North Carolina at Chapel Hill Lecture 5: Syntax Analysis COMP 144 Programming Language Concepts Spring 2002 Felix Hernandez-Campos Jan 18 COMP 144 Programming Language Concepts Felix Hernandez-Campos

  2. Source Code Interpre- tation Target Code Review: Compilation/Interpretation Compiler or Interpreter Translation Execution COMP 144 Programming Language Concepts Felix Hernandez-Campos

  3. Review: Syntax Analysis • Specifying the form of a programming language • Tokens • Regular Expression • Syntax • Context-Free Grammars Source Code Compiler or Interpreter Translation Execution Target Code COMP 144 Programming Language Concepts Felix Hernandez-Campos

  4. Phases of Compilation COMP 144 Programming Language Concepts Felix Hernandez-Campos

  5. Syntax Analysis • Syntax: • Webster’s definition: 1 a : the way in which linguistic elements (as words) are put together to form constituents (as phrases or clauses) • The syntax of a programming language • Describes its form • Organization of tokens(elements) • Context Free Grammars (CFGs) • Must be recognizable by compilers and interpreters • Parsing • LL and LR parsers COMP 144 Programming Language Concepts Felix Hernandez-Campos

  6. Context Free Grammars • CFGs • Add recursion to regular expressions • Nested constructions • Notation expression identifier | number| -expression | (expression) | expressionoperatorexpression operator  + | -| *| / • Terminal symbols • Non-terminal symbols • Production rule (i.e. substitution rule) terminal symbol  terminal and non-terminal symbols COMP 144 Programming Language Concepts Felix Hernandez-Campos

  7. Parsers • Scanners • Task: recognize language tokens • Implementation: Deterministic Finite Automaton • Transition based on the next character • Parsers • Task: recognize language syntax (organization of tokens) • Implementation: • Top-down parsing • Bottom-up parsing COMP 144 Programming Language Concepts Felix Hernandez-Campos

  8. Parse Trees • A parse is graphical representation of a derivation • Example COMP 144 Programming Language Concepts Felix Hernandez-Campos

  9. Parsing example • Example: comma-separated list of identifier • CFG id_list  idid_list_tail id_list_tail  ,id_list_tail id_list_tail  ; • Parsing A, B, C; COMP 144 Programming Language Concepts Felix Hernandez-Campos

  10. Left-to-right, Left-most derivation LL(1) parsing Top-down derivation of A, B, C; CFG COMP 144 Programming Language Concepts Felix Hernandez-Campos

  11. Top-down derivation of A, B, C; CFG COMP 144 Programming Language Concepts Felix Hernandez-Campos

  12. Bottom-up parsing of A, B, C; CFG Left-to-right, Right-most derivation LR(1) parsing COMP 144 Programming Language Concepts Felix Hernandez-Campos

  13. Bottom-up parsing of A, B, C; CFG COMP 144 Programming Language Concepts Felix Hernandez-Campos

  14. Bottom-up parsing of A, B, C; CFG COMP 144 Programming Language Concepts Felix Hernandez-Campos

  15. Parsing • Parsing an arbitrary Context Free Grammar • O(n3) • Too slow for large programs • Linear-time parsing • LL parsers • Recognize LL grammar • Use a top-down strategy • LR parsers • Recognize LR grammar • Use a bottom-up strategy COMP 144 Programming Language Concepts Felix Hernandez-Campos

  16. Hierarchy of Linear Parsers • Basic containment relationship • All CFGs can be recognized by LR parser • Only a subset of all the CFGs can be recognized by LL parsers CFGsLR parsing LL parsing COMP 144 Programming Language Concepts Felix Hernandez-Campos

  17. Recursive Descent Parser Example • LL(1) grammar COMP 144 Programming Language Concepts Felix Hernandez-Campos

  18. Recursive Descent Parser Example • Outline of recursive parser • This parser only verifies syntax • match is the scanner COMP 144 Programming Language Concepts Felix Hernandez-Campos

  19. Recursive Descent Parser Example COMP 144 Programming Language Concepts Felix Hernandez-Campos

  20. Recursive Descent Parser Example COMP 144 Programming Language Concepts Felix Hernandez-Campos

  21. Recursive Descent Parser Example COMP 144 Programming Language Concepts Felix Hernandez-Campos

  22. Semantic Analysis • Specifying the meaning of a programming language • Attribute Grammars Source Code Compiler or Interpreter Translation Execution Target Code COMP 144 Programming Language Concepts Felix Hernandez-Campos

  23. Reading Assignment • Scott’s Chapter 2 • Section 2.2.2 • Section 2.2.3 COMP 144 Programming Language Concepts Felix Hernandez-Campos

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