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Formal languages and Compiler Design

Formal languages and Compiler Design. Simona Motogna. Why ?. Organization Issues. Course – 2 h/ week Seminar – 2h/week Laboratory - 2 h/week PRESENCE IS MANDATORY. 10 presences – seminar 12 presences - lab. Organization Issues. Final grade = 70% written exam + 20% lab

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Formal languages and Compiler Design

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  1. Formal languages and Compiler Design Simona Motogna S. Motogna - LFTC

  2. Why? S. Motogna - LFTC

  3. Organization Issues • Course – 2 h/ week • Seminar – 2h/week • Laboratory - 2 h/week PRESENCE IS MANDATORY 10 presences – seminar 12 presences - lab S. Motogna - LFTC

  4. Organization Issues • Final grade = 70% written exam + 20% lab + 10% seminar Lab: - all laboratory assignments are mandatory - delays NO more than 2 weeks Seminar: - solved problems, answers (blackboard), homeworks S. Motogna - LFTC

  5. References • See fișa disciplinei S. Motogna - LFTC

  6. What is a compiler? Interpreter? Object code / program Source code / program Compiler Assembler? S. Motogna - LFTC

  7. A little bit of history … • Java • 1995 • J. Gosling • C • 1969 - 1973 • D. Ritchie • Pascal • 1968 - 1970 • N. Wirth • Lisp • 1962 • McCarthy • Fortran • 1954-1957 • Backus S. Motogna - LFTC

  8. Structure of a compiler Error handling analysis Source code/ program tokens Syntax tree synthesis Adnotated syntax tree Symbol Table management Intermediary code Object code / program Optimized intermediary code S. Motogna - LFTC

  9. Chapter 1. Scanning Definition = treats the source program as a sequence of characters, detect lexical tokens, classify and codify them INPUT: source program OUTPUT: PIF + ST Algorithm Scanning v1 While (not(eof)) do detect(token); classify(token); codify(token); End_while S. Motogna - LFTC

  10. Detect I am a student. • Separators => Remark 1) + 2) • Look-ahead => Remark 3) if (x==y) {x=y+2} S. Motogna - LFTC

  11. Classify • Classes of tokens: • Identifiers • Constants • Reserved words (keywords) • Separators • Operators • If a token can NOT be classified => LEXICAL ERROR S. Motogna - LFTC

  12. Codify • Codification table • Identifier, constant => Symbol Table (ST) • PIF = Program Internal Form = array of pairs • Token – replaced by pair (code, position in ST) identifier, constant S. Motogna - LFTC

  13. Algorithm Scanning v2 While (not(eof)) do detect(token); iftoken is reserved word OR operator OR separator thengenFIP(code, 0) else if token is identifier OR constant then index = pos(token, ST); genFIP(code, index) else message “Lexical error” endif endif endwhile S. Motogna - LFTC

  14. Remarks: • genFIP = adds a pair (code, position) to PIF • Pos(token,ST) – searches token in symbol table ST; if found then return position; if not found insert in SR and return position • Order of classification (reserved word, then identifier) • If-then-else imbricate => detect error if a token cannot be classified S. Motogna - LFTC

  15. Symbol Table Definition = contains all information collected during compiling regarding the symbolic names from the source program identifiers, constants, etc. Variants: - Unique symbol table – contains all symbolic names - distinct symbol tables: IT (identifiers table) + CT (constants table) S. Motogna - LFTC

  16. ST organization Remark: search and insert • Unsorted table – in order of detection in source code O(n) • Sorted table: alphabetic (numeric) O(lg n) • Binary search tree (balanced) O(lg n) • Hash table O(1) S. Motogna - LFTC

  17. Hash table • K = set of keys (symbolic names) • A = set of positions (|A| = m; m –prime number) h : K → A h(k) = (val(k) mod m) + 1 • Conflicts: k1 ≠ k2 , h(k1) = h(k2) S. Motogna - LFTC

  18. Visibility domain (scope) • Each scope – separate ST • Structure -> inclusion tree S. Motogna - LFTC

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