Context-Free Languages. Wen-Guey Tzeng Department of Computer Science National Chiao Tung University
|
|
- Tamsyn Turner
- 5 years ago
- Views:
Transcription
1 Context-Free Languages Wen-Guey Tzeng Department of Computer Science National Chiao Tung University
2 Context-Free Grammars A grammar G=(V, T, S, P) is context-free if all productions in P are of form A x, where A V, x (V T)* The left side has only one variable. Example, G = ({S,A,B}, {a,b}, S, {S aab bba, A aab, B bbb }) 2
3 Derivation: 3
4 L(G) = {w * S * w} A language L is context-free if and only if there is a context-free grammar G such that L=L(G). 4
5 Examples G=({S}, {a, b}, S, P), with P={S asa bsb } S asa aasaa aabsbaa aab baa=aabbaa L(G) = {ww R : w {a, b}*} 5
6 S abb, A aabb, B bbaa L(G) = {ab(bbaa) n bba(ba) n : n 0}? 6
7 Design cfg s Give a cfg for L={a n b n : n 0} 7
8 Give a cfg for L={a n b m : n>m} 8
9 Give a cfg for L={a n b m : n m 0} Idea1: parse L into two cases (not necessarily disjoint) L 1 ={a n b m : n>m} L 2 ={a n b m : n<m}. Then, construct productions for L 1 and L 2, respectively. 9
10 Give a cfg for L={a n b m : n m 0} Idea2: produce the same amount of a s and b s, then extra a s or b s 10
11 Give a cfg for L={a n b m c k : m=n+k} Match a and b, b and c 11
12 Give a cfg for L={a n b m c k : m>n+k} 12
13 Give a cfg for L={w {a,b}* : n a (w)=n b (w)} Find the recursion 13
14 Give a cfg for L={w {a,b}* : n a (w)>n b (w)} Find relation with other language Consider starting with a and b, respectively 14
15 Leftmost and rightmost derivation G=({A, B, S}, {a, b}, S, P), where P contains S AB, A aaa, A, B Bb, B L(G)={a 2n b m : n, m 0} For string aab Rightmost derivation Leftmost derivation 15
16 Derivation (parse) tree A ababc 16
17 S aab, A bbb, B A 17
18 Some comments Derivation trees represent no orders of derivation Leftmost/rightmost derivations correspond to depth-first visiting of the tree Derivation tree and derivation order are very important to programming language and compiler design 18
19 Grammar for C 19
20 main() { int i=1; printf("i starts out life as %d.", i); i = add(1, 1); /* Function call */ printf(" And becomes %d after function is executed.\n", i); } 20
21 Parsing and ambiguity Parsing of w L(G): find a sequence of productions by which w L(G) is derived. Questions: given G and w Is w L(G)? (membership problem) Efficient way to determine whether w L(G)? How is w L(G) parsed? (build the parsing tree) Is the parsing unique? 21
22 Exhaustive search/top down parsing S SS asb bsa Determine aabb L(G)? 1 st round: (1) S SS; (2) S asb; (3) S bsa; (4) S 2 nd round: From (1), S SS SSS, S SS asbs, S SS bsas, S SS S From (2), S asb assb, S asb aasbb, S asb absab, S asb ab 3 rd round: Drawback: inefficiency Other ways? 22
23 If no productions of form A or A B, the exhaustive search for w L(G) can be done in P + P P 2 w = O( P 2 w +1 ) Consider the leftmost parsing method. w can be obtained within 2 w derivations. 23
24 Bottom up parsing To reduce a string w to the start variable S S asb w=aabb aasbb asb S Efficiency: O( w 3 ) 24
25 Linear-time parsing Simple grammar (s-grammar) All productions are of form A ax, where x (V T)* Any pair (A, a) occurs at most once in P. Example: S as bss c Parsing for ababccc 25
26 Ambiguous grammars G is ambiguous if some w L(G) has two derivation trees. Example: S asb SS 26
27 Example from programming languages C-like grammar for arithmetic expressions. G=({E, I}, {a, b, c, +, x, (, )}, E, P), where P contains E I E E+E E ExE E (E) I a b c w=a+bxc has two derivation trees 27
28 28
29 Ambiguous languages A cfl L is inherently ambiguous if any cfg G with L(G)=L is ambiguous. Otherwise, it is unambiguous. Note: an unambiguous language may have ambiguous grammar. Example: L={a n b n c m } {a n b m c m } is inherently ambigous. Hard to prove. 29
30 CFG and Programming Languages Programming language: syntax + semantics Syntax is defined by a grammar G <expression> ::= <term> <expression> + <term> <term> ::= <factor> <term> * <factor> <while_statement> ::= while <expression><statement> Syntax checking in compilers is done by a parser Is a program p grammatically correct? Is p L(G)? We need efficient parsers. 30
31 Goal: Restricted CFG Programming Languages Its expression power is enough. It has no ambiguity. if then if then else If then if then else If then if then else There exists an efficient parser. 31
32 C -- LR(1) PASCAL -- LL(1) Hierarchy of classes of context-free languages LL(1) LR(0) LR(1)=DCFL LR(2) CFL 32
33 Syntactic Correctness Lexical analyzer produces a stream of tokens x = y +2.1 <id> <op> <id> <op> <real> Parser (syntactic analyzer) verifies that this token stream is syntactically correct by constructing a valid parse tree for the entire program Unique parse tree for each language construct Program = collection of parse trees rooted at the top by a special start symbol slide 33
34 CFG For Floating Point Numbers ::= stands for production rule; < > are non-terminals; represents alternatives for the right-hand side of a production rule Sample parse tree: slide 34
35 CFG For Balanced Parentheses Could we write this grammar using regular expressions or DFA? Why? Sample derivation: <balanced> ( <balanced> ) (( <balanced> )) (( <empty> )) (( )) slide 35
36 CFG For Decimal Numbers (Redux) This grammar is right-recursive Sample top-down leftmost derivation: <num> <digit> <num> 7 <num> 7 <digit> <num> 7 8 <num> 7 8 <digit> slide 36
37 Compiler-compiler A compiler-compiler is a program that generates a compiler from a defined grammar Parser can be built automatically from the BNF description of the language s CFG Tools: yacc, Bison slide 37
38 program Programming language grammar G=(V, T, S, P) Compilercompiler Compiler: parser + code generator Input data Execution code result slide 38
Context-Free Languages. Wen-Guey Tzeng Department of Computer Science National Chiao Tung University
Context-Free Languages Wen-Guey Tzeng Department of Computer Science National Chiao Tung University Context-Free Grammars A grammar G=(V, T, S, P) is context-free if all productions in P are of form A
More informationContext-Free Languages. Wen-Guey Tzeng Department of Computer Science National Chiao Tung University
Context-Free Languages Wen-Guey Tzeng Department of Computer Science National Chiao Tung University Context-Free Grammars A grammar G=(V, T, S, P) is context-free if all productions in P are of form A
More informationContext-Free Languages. Wen-Guey Tzeng Department of Computer Science National Chiao Tung University
Context-Free Languages Wen-Guey Tzeng Department of Computer Science National Chiao Tung University 1 Context-Free Grammars Some languages are not regular. Eg. L={a n b n : n 0} A grammar G=(V, T, S, P)
More informationChapter 3: CONTEXT-FREE GRAMMARS AND PARSING Part 1
Chapter 3: CONTEXT-FREE GRAMMARS AND PARSING Part 1 1. Introduction Parsing is the task of Syntax Analysis Determining the syntax, or structure, of a program. The syntax is defined by the grammar rules
More informationCOP 3402 Systems Software Syntax Analysis (Parser)
COP 3402 Systems Software Syntax Analysis (Parser) Syntax Analysis 1 Outline 1. Definition of Parsing 2. Context Free Grammars 3. Ambiguous/Unambiguous Grammars Syntax Analysis 2 Lexical and Syntax Analysis
More informationCompiler Construction
Compiler Construction Exercises 1 Review of some Topics in Formal Languages 1. (a) Prove that two words x, y commute (i.e., satisfy xy = yx) if and only if there exists a word w such that x = w m, y =
More informationCMSC 330: Organization of Programming Languages. Context-Free Grammars Ambiguity
CMSC 330: Organization of Programming Languages Context-Free Grammars Ambiguity Review Why should we study CFGs? What are the four parts of a CFG? How do we tell if a string is accepted by a CFG? What
More informationCMSC 330: Organization of Programming Languages
CMSC 330: Organization of Programming Languages Context Free Grammars and Parsing 1 Recall: Architecture of Compilers, Interpreters Source Parser Static Analyzer Intermediate Representation Front End Back
More informationJNTUWORLD. Code No: R
Code No: R09220504 R09 SET-1 B.Tech II Year - II Semester Examinations, April-May, 2012 FORMAL LANGUAGES AND AUTOMATA THEORY (Computer Science and Engineering) Time: 3 hours Max. Marks: 75 Answer any five
More informationEECS 6083 Intro to Parsing Context Free Grammars
EECS 6083 Intro to Parsing Context Free Grammars Based on slides from text web site: Copyright 2003, Keith D. Cooper, Ken Kennedy & Linda Torczon, all rights reserved. 1 Parsing sequence of tokens parser
More informationCMSC 330: Organization of Programming Languages
CMSC 330: Organization of Programming Languages Context Free Grammars 1 Architecture of Compilers, Interpreters Source Analyzer Optimizer Code Generator Abstract Syntax Tree Front End Back End Compiler
More informationCMSC 330: Organization of Programming Languages. Architecture of Compilers, Interpreters
: Organization of Programming Languages Context Free Grammars 1 Architecture of Compilers, Interpreters Source Scanner Parser Static Analyzer Intermediate Representation Front End Back End Compiler / Interpreter
More informationContext-Free Languages & Grammars (CFLs & CFGs) Reading: Chapter 5
Context-Free Languages & Grammars (CFLs & CFGs) Reading: Chapter 5 1 Not all languages are regular So what happens to the languages which are not regular? Can we still come up with a language recognizer?
More informationQUESTIONS RELATED TO UNIT I, II And III
QUESTIONS RELATED TO UNIT I, II And III UNIT I 1. Define the role of input buffer in lexical analysis 2. Write regular expression to generate identifiers give examples. 3. Define the elements of production.
More informationCMSC 330: Organization of Programming Languages. Context Free Grammars
CMSC 330: Organization of Programming Languages Context Free Grammars 1 Architecture of Compilers, Interpreters Source Analyzer Optimizer Code Generator Abstract Syntax Tree Front End Back End Compiler
More informationCMSC 330: Organization of Programming Languages. Context Free Grammars
CMSC 330: Organization of Programming Languages Context Free Grammars 1 Architecture of Compilers, Interpreters Source Analyzer Optimizer Code Generator Abstract Syntax Tree Front End Back End Compiler
More informationCPS 506 Comparative Programming Languages. Syntax Specification
CPS 506 Comparative Programming Languages Syntax Specification Compiling Process Steps Program Lexical Analysis Convert characters into a stream of tokens Lexical Analysis Syntactic Analysis Send tokens
More informationFormal Languages and Compilers Lecture V: Parse Trees and Ambiguous Gr
Formal Languages and Compilers Lecture V: Parse Trees and Ambiguous Grammars Free University of Bozen-Bolzano Faculty of Computer Science POS Building, Room: 2.03 artale@inf.unibz.it http://www.inf.unibz.it/
More informationWhere We Are. CMSC 330: Organization of Programming Languages. This Lecture. Programming Languages. Motivation for Grammars
CMSC 330: Organization of Programming Languages Context Free Grammars Where We Are Programming languages Ruby OCaml Implementing programming languages Scanner Uses regular expressions Finite automata Parser
More informationCMSC 330: Organization of Programming Languages
CMSC 330: Organization of Programming Languages Context Free Grammars 1 Architecture of Compilers, Interpreters Source Analyzer Optimizer Code Generator Abstract Syntax Tree Front End Back End Compiler
More informationA simple syntax-directed
Syntax-directed is a grammaroriented compiling technique Programming languages: Syntax: what its programs look like? Semantic: what its programs mean? 1 A simple syntax-directed Lexical Syntax Character
More informationContext-Free Grammars
Context-Free Grammars 1 Informal Comments A context-free grammar is a notation for describing languages. It is more powerful than finite automata or RE s, but still cannot define all possible languages.
More informationR10 SET a) Construct a DFA that accepts an identifier of a C programming language. b) Differentiate between NFA and DFA?
R1 SET - 1 1. a) Construct a DFA that accepts an identifier of a C programming language. b) Differentiate between NFA and DFA? 2. a) Design a DFA that accepts the language over = {, 1} of all strings that
More informationCS 2210 Sample Midterm. 1. Determine if each of the following claims is true (T) or false (F).
CS 2210 Sample Midterm 1. Determine if each of the following claims is true (T) or false (F). F A language consists of a set of strings, its grammar structure, and a set of operations. (Note: a language
More informationContext-Free Grammars and Languages (2015/11)
Chapter 5 Context-Free Grammars and Languages (2015/11) Adriatic Sea shore at Opatija, Croatia Outline 5.0 Introduction 5.1 Context-Free Grammars (CFG s) 5.2 Parse Trees 5.3 Applications of CFG s 5.4 Ambiguity
More informationQUESTION BANK. Formal Languages and Automata Theory(10CS56)
QUESTION BANK Formal Languages and Automata Theory(10CS56) Chapter 1 1. Define the following terms & explain with examples. i) Grammar ii) Language 2. Mention the difference between DFA, NFA and εnfa.
More informationContext-Free Grammars
Context-Free Grammars Describing Languages We've seen two models for the regular languages: Finite automata accept precisely the strings in the language. Regular expressions describe precisely the strings
More information2068 (I) Attempt all questions.
2068 (I) 1. What do you mean by compiler? How source program analyzed? Explain in brief. 2. Discuss the role of symbol table in compiler design. 3. Convert the regular expression 0 + (1 + 0)* 00 first
More informationChapter 3: Describing Syntax and Semantics. Introduction Formal methods of describing syntax (BNF)
Chapter 3: Describing Syntax and Semantics Introduction Formal methods of describing syntax (BNF) We can analyze syntax of a computer program on two levels: 1. Lexical level 2. Syntactic level Lexical
More informationCS415 Compilers. Syntax Analysis. These slides are based on slides copyrighted by Keith Cooper, Ken Kennedy & Linda Torczon at Rice University
CS415 Compilers Syntax Analysis These slides are based on slides copyrighted by Keith Cooper, Ken Kennedy & Linda Torczon at Rice University Limits of Regular Languages Advantages of Regular Expressions
More informationIntroduction to Parsing. Lecture 8
Introduction to Parsing Lecture 8 Adapted from slides by G. Necula Outline Limitations of regular languages Parser overview Context-free grammars (CFG s) Derivations Languages and Automata Formal languages
More informationPlan for Today. Regular Expressions: repetition and choice. Syntax and Semantics. Context Free Grammars
Plan for Today Context Free s models for specifying programming languages syntax semantics example grammars derivations Parse trees yntax-directed translation Used syntax-directed translation to interpret
More informationIntroduction to Parsing
Introduction to Parsing The Front End Source code Scanner tokens Parser IR Errors Parser Checks the stream of words and their parts of speech (produced by the scanner) for grammatical correctness Determines
More informationCS 315 Programming Languages Syntax. Parser. (Alternatively hand-built) (Alternatively hand-built)
Programming languages must be precise Remember instructions This is unlike natural languages CS 315 Programming Languages Syntax Precision is required for syntax think of this as the format of the language
More informationCSE450 Translation of Programming Languages. Lecture 4: Syntax Analysis
CSE450 Translation of Programming Languages Lecture 4: Syntax Analysis http://xkcd.com/859 Structure of a Today! Compiler Source Language Lexical Analyzer Syntax Analyzer Semantic Analyzer Int. Code Generator
More informationOutline. Limitations of regular languages. Introduction to Parsing. Parser overview. Context-free grammars (CFG s)
Outline Limitations of regular languages Introduction to Parsing Parser overview Lecture 8 Adapted from slides by G. Necula Context-free grammars (CFG s) Derivations Languages and Automata Formal languages
More informationPrinciples of Programming Languages COMP251: Syntax and Grammars
Principles of Programming Languages COMP251: Syntax and Grammars Prof. Dekai Wu Department of Computer Science and Engineering The Hong Kong University of Science and Technology Hong Kong, China Fall 2006
More informationQuestion Bank. 10CS63:Compiler Design
Question Bank 10CS63:Compiler Design 1.Determine whether the following regular expressions define the same language? (ab)* and a*b* 2.List the properties of an operator grammar 3. Is macro processing a
More informationSyntax-Directed Translation. Lecture 14
Syntax-Directed Translation Lecture 14 (adapted from slides by R. Bodik) 9/27/2006 Prof. Hilfinger, Lecture 14 1 Motivation: parser as a translator syntax-directed translation stream of tokens parser ASTs,
More informationSection A. A grammar that produces more than one parse tree for some sentences is said to be ambiguous.
Section A 1. What do you meant by parser and its types? A parser for grammar G is a program that takes as input a string w and produces as output either a parse tree for w, if w is a sentence of G, or
More informationITEC2620 Introduction to Data Structures
ITEC2620 Introduction to Data Structures Lecture 9b Grammars I Overview How can a computer do Natural Language Processing? Grammar checking? Artificial Intelligence Represent knowledge so that brute force
More information1. The output of lexical analyser is a) A set of RE b) Syntax Tree c) Set of Tokens d) String Character
1. The output of lexical analyser is a) A set of RE b) Syntax Tree c) Set of Tokens d) String Character 2. The symbol table implementation is based on the property of locality of reference is a) Linear
More informationParsing II Top-down parsing. Comp 412
COMP 412 FALL 2018 Parsing II Top-down parsing Comp 412 source code IR Front End Optimizer Back End IR target code Copyright 2018, Keith D. Cooper & Linda Torczon, all rights reserved. Students enrolled
More informationSYED AMMAL ENGINEERING COLLEGE (An ISO 9001:2008 Certified Institution) Dr. E.M. Abdullah Campus, Ramanathapuram
CS6660 COMPILER DESIGN Question Bank UNIT I-INTRODUCTION TO COMPILERS 1. Define compiler. 2. Differentiate compiler and interpreter. 3. What is a language processing system? 4. List four software tools
More informationCS375: Logic and Theory of Computing
CS375: Logic and Theory of Computing Fuhua (Frank) Cheng Department of Computer Science University of Kentucky 1 Table of Contents: Week 1: Preliminaries (set algebra, relations, functions) (read Chapters
More informationDownloaded from Page 1. LR Parsing
Downloaded from http://himadri.cmsdu.org Page 1 LR Parsing We first understand Context Free Grammars. Consider the input string: x+2*y When scanned by a scanner, it produces the following stream of tokens:
More informationIntroduction to Syntax Analysis
Compiler Design 1 Introduction to Syntax Analysis Compiler Design 2 Syntax Analysis The syntactic or the structural correctness of a program is checked during the syntax analysis phase of compilation.
More informationChapter 3. Topics. Languages. Formal Definition of Languages. BNF and Context-Free Grammars. Grammar 2/4/2019
Chapter 3. Topics The terms of Syntax, Syntax Description Method: Context-Free Grammar (Backus-Naur Form) Derivation Parse trees Ambiguity Operator precedence and associativity Extended Backus-Naur Form
More informationArchitecture of Compilers, Interpreters. CMSC 330: Organization of Programming Languages. Front End Scanner and Parser. Implementing the Front End
Architecture of Compilers, Interpreters : Organization of Programming Languages ource Analyzer Optimizer Code Generator Context Free Grammars Intermediate Representation Front End Back End Compiler / Interpreter
More informationCS 314 Principles of Programming Languages
CS 314 Principles of Programming Languages Lecture 5: Syntax Analysis (Parsing) Zheng (Eddy) Zhang Rutgers University January 31, 2018 Class Information Homework 1 is being graded now. The sample solution
More informationLexical Analysis (ASU Ch 3, Fig 3.1)
Lexical Analysis (ASU Ch 3, Fig 3.1) Implementation by hand automatically ((F)Lex) Lex generates a finite automaton recogniser uses regular expressions Tasks remove white space (ws) display source program
More informationΕΠΛ323 - Θεωρία και Πρακτική Μεταγλωττιστών
ΕΠΛ323 - Θεωρία και Πρακτική Μεταγλωττιστών Lecture 5a Syntax Analysis lias Athanasopoulos eliasathan@cs.ucy.ac.cy Syntax Analysis Συντακτική Ανάλυση Context-free Grammars (CFGs) Derivations Parse trees
More informationDr. D.M. Akbar Hussain
Syntax Analysis Parsing Syntax Or Structure Given By Determines Grammar Rules Context Free Grammar 1 Context Free Grammars (CFG) Provides the syntactic structure: A grammar is quadruple (V T, V N, S, R)
More informationIntroduction to Syntax Analysis. The Second Phase of Front-End
Compiler Design IIIT Kalyani, WB 1 Introduction to Syntax Analysis The Second Phase of Front-End Compiler Design IIIT Kalyani, WB 2 Syntax Analysis The syntactic or the structural correctness of a program
More informationPrinciples of Programming Languages COMP251: Syntax and Grammars
Principles of Programming Languages COMP251: Syntax and Grammars Prof. Dekai Wu Department of Computer Science and Engineering The Hong Kong University of Science and Technology Hong Kong, China Fall 2007
More informationWriting a Simple DSL Compiler with Delphi. Primož Gabrijelčič / primoz.gabrijelcic.org
Writing a Simple DSL Compiler with Delphi Primož Gabrijelčič / primoz.gabrijelcic.org About me Primož Gabrijelčič http://primoz.gabrijelcic.org programmer, MVP, writer, blogger, consultant, speaker Blog
More informationOutline. Parser overview Context-free grammars (CFG s) Derivations Syntax-Directed Translation
Outline Introduction to Parsing (adapted from CS 164 at Berkeley) Parser overview Context-free grammars (CFG s) Derivations Syntax-Directed ranslation he Functionality of the Parser Input: sequence of
More informationParsing. source code. while (k<=n) {sum = sum+k; k=k+1;}
Compiler Construction Grammars Parsing source code scanner tokens regular expressions lexical analysis Lennart Andersson parser context free grammar Revision 2012 01 23 2012 parse tree AST builder (implicit)
More informationCompiler Design Concepts. Syntax Analysis
Compiler Design Concepts Syntax Analysis Introduction First task is to break up the text into meaningful words called tokens. newval=oldval+12 id = id + num Token Stream Lexical Analysis Source Code (High
More informationContext-Free Grammars
Context-Free Grammars Describing Languages We've seen two models for the regular languages: Finite automata accept precisely the strings in the language. Regular expressions describe precisely the strings
More information1. Which of the following regular expressions over {0, 1} denotes the set of all strings not containing 100 as a sub-string?
Multiple choice type questions. Which of the following regular expressions over {, } denotes the set of all strings not containing as a sub-string? 2. DFA has a) *(*)* b) ** c) ** d) *(+)* a) single final
More informationContext-Free Grammars
Context-Free Grammars Lecture 7 http://webwitch.dreamhost.com/grammar.girl/ Outline Scanner vs. parser Why regular expressions are not enough Grammars (context-free grammars) grammar rules derivations
More informationFall Compiler Principles Context-free Grammars Refresher. Roman Manevich Ben-Gurion University of the Negev
Fall 2016-2017 Compiler Principles Context-free Grammars Refresher Roman Manevich Ben-Gurion University of the Negev 1 xample grammar S S ; S S id := S print (L) id num + L L L, shorthand for Statement
More informationParsing. Note by Baris Aktemur: Our slides are adapted from Cooper and Torczon s slides that they prepared for COMP 412 at Rice.
Parsing Note by Baris Aktemur: Our slides are adapted from Cooper and Torczon s slides that they prepared for COMP 412 at Rice. Copyright 2010, Keith D. Cooper & Linda Torczon, all rights reserved. Students
More informationSyntax Analysis Check syntax and construct abstract syntax tree
Syntax Analysis Check syntax and construct abstract syntax tree if == = ; b 0 a b Error reporting and recovery Model using context free grammars Recognize using Push down automata/table Driven Parsers
More informationCompilers and computer architecture From strings to ASTs (2): context free grammars
1 / 1 Compilers and computer architecture From strings to ASTs (2): context free grammars Martin Berger October 2018 Recall the function of compilers 2 / 1 3 / 1 Recall we are discussing parsing Source
More informationCT32 COMPUTER NETWORKS DEC 2015
Q.2 a. Using the principle of mathematical induction, prove that (10 (2n-1) +1) is divisible by 11 for all n N (8) Let P(n): (10 (2n-1) +1) is divisible by 11 For n = 1, the given expression becomes (10
More informationQUESTION BANK. Unit 1. Introduction to Finite Automata
QUESTION BANK Unit 1 Introduction to Finite Automata 1. Obtain DFAs to accept strings of a s and b s having exactly one a.(5m )(Jun-Jul 10) 2. Obtain a DFA to accept strings of a s and b s having even
More informationMultiple Choice Questions
Techno India Batanagar Computer Science and Engineering Model Questions Subject Name: Formal Language and Automata Theory Subject Code: CS 402 Multiple Choice Questions 1. The basic limitation of an FSM
More informationDerivations vs Parses. Example. Parse Tree. Ambiguity. Different Parse Trees. Context Free Grammars 9/18/2012
Derivations vs Parses Grammar is used to derive string or construct parser Context ree Grammars A derivation is a sequence of applications of rules Starting from the start symbol S......... (sentence)
More informationPart 3. Syntax analysis. Syntax analysis 96
Part 3 Syntax analysis Syntax analysis 96 Outline 1. Introduction 2. Context-free grammar 3. Top-down parsing 4. Bottom-up parsing 5. Conclusion and some practical considerations Syntax analysis 97 Structure
More informationSyntax Analysis. COMP 524: Programming Language Concepts Björn B. Brandenburg. The University of North Carolina at Chapel Hill
Syntax Analysis Björn B. Brandenburg The University of North Carolina at Chapel Hill Based on slides and notes by S. Olivier, A. Block, N. Fisher, F. Hernandez-Campos, and D. Stotts. The Big Picture Character
More informationProgramming Languages & Translators PARSING. Baishakhi Ray. Fall These slides are motivated from Prof. Alex Aiken: Compilers (Stanford)
Programming Languages & Translators PARSING Baishakhi Ray Fall 2018 These slides are motivated from Prof. Alex Aiken: Compilers (Stanford) Languages and Automata Formal languages are very important in
More informationCSE443 Compilers. Dr. Carl Alphonce 343 Davis Hall
CSE443 Compilers Dr. Carl Alphonce alphonce@buffalo.edu 343 Davis Hall Phases of a compiler Syntactic structure Figure 1.6, page 5 of text Recap Lexical analysis: LEX/FLEX (regex -> lexer) Syntactic analysis:
More informationSyntax Analysis. The Big Picture. The Big Picture. COMP 524: Programming Languages Srinivas Krishnan January 25, 2011
Syntax Analysis COMP 524: Programming Languages Srinivas Krishnan January 25, 2011 Based in part on slides and notes by Bjoern Brandenburg, S. Olivier and A. Block. 1 The Big Picture Character Stream Token
More informationSyntax. In Text: Chapter 3
Syntax In Text: Chapter 3 1 Outline Syntax: Recognizer vs. generator BNF EBNF Chapter 3: Syntax and Semantics 2 Basic Definitions Syntax the form or structure of the expressions, statements, and program
More informationEDAN65: Compilers, Lecture 04 Grammar transformations: Eliminating ambiguities, adapting to LL parsing. Görel Hedin Revised:
EDAN65: Compilers, Lecture 04 Grammar transformations: Eliminating ambiguities, adapting to LL parsing Görel Hedin Revised: 2017-09-04 This lecture Regular expressions Context-free grammar Attribute grammar
More informationSyntax Analysis Top Down Parsing
Syntax Analysis Top Down Parsing CMPSC 470 Lecture 05 Topics: Overview Recursive-descent parser First and Follow A. Overview Top-down parsing constructs parse tree for input string from root and creating
More informationLecture 4: Syntax Specification
The University of North Carolina at Chapel Hill Spring 2002 Lecture 4: Syntax Specification Jan 16 1 Phases of Compilation 2 1 Syntax Analysis Syntax: Webster s definition: 1 a : the way in which linguistic
More informationUNIT I PART A PART B
OXFORD ENGINEERING COLLEGE (NAAC ACCREDITED WITH B GRADE) DEPARTMENT OF COMPUTER SCIENCE & ENGINEERING LIST OF QUESTIONS YEAR/SEM: III/V STAFF NAME: Dr. Sangeetha Senthilkumar SUB.CODE: CS6503 SUB.NAME:
More informationA Simple Syntax-Directed Translator
Chapter 2 A Simple Syntax-Directed Translator 1-1 Introduction The analysis phase of a compiler breaks up a source program into constituent pieces and produces an internal representation for it, called
More informationCMPT 755 Compilers. Anoop Sarkar.
CMPT 755 Compilers Anoop Sarkar http://www.cs.sfu.ca/~anoop Parsing source program Lexical Analyzer token next() Parser parse tree Later Stages Lexical Errors Syntax Errors Context-free Grammars Set of
More informationCSCI312 Principles of Programming Languages!
CSCI312 Principles of Programming Languages!! Chapter 3 Regular Expression and Lexer Xu Liu Recap! Copyright 2006 The McGraw-Hill Companies, Inc. Clite: Lexical Syntax! Input: a stream of characters from
More informationCSE 3302 Programming Languages Lecture 2: Syntax
CSE 3302 Programming Languages Lecture 2: Syntax (based on slides by Chengkai Li) Leonidas Fegaras University of Texas at Arlington CSE 3302 L2 Spring 2011 1 How do we define a PL? Specifying a PL: Syntax:
More informationCompilers. Yannis Smaragdakis, U. Athens (original slides by Sam
Compilers Parsing Yannis Smaragdakis, U. Athens (original slides by Sam Guyer@Tufts) Next step text chars Lexical analyzer tokens Parser IR Errors Parsing: Organize tokens into sentences Do tokens conform
More informationSyntax Analysis. Chapter 4
Syntax Analysis Chapter 4 Check (Important) http://www.engineersgarage.com/contributio n/difference-between-compiler-andinterpreter Introduction covers the major parsing methods that are typically used
More informationCOP4020 Programming Languages. Syntax Prof. Robert van Engelen
COP4020 Programming Languages Syntax Prof. Robert van Engelen Overview n Tokens and regular expressions n Syntax and context-free grammars n Grammar derivations n More about parse trees n Top-down and
More informationRecursive Descent Parsers
Recursive Descent Parsers Lecture 7 Robb T. Koether Hampden-Sydney College Wed, Jan 28, 2015 Robb T. Koether (Hampden-Sydney College) Recursive Descent Parsers Wed, Jan 28, 2015 1 / 18 1 Parsing 2 LL Parsers
More informationCS 321 Programming Languages and Compilers. VI. Parsing
CS 321 Programming Languages and Compilers VI. Parsing Parsing Calculate grammatical structure of program, like diagramming sentences, where: Tokens = words Programs = sentences For further information,
More informationChapter 3: CONTEXT-FREE GRAMMARS AND PARSING Part2 3.3 Parse Trees and Abstract Syntax Trees
Chapter 3: CONTEXT-FREE GRAMMARS AND PARSING Part2 3.3 Parse Trees and Abstract Syntax Trees 3.3.1 Parse trees 1. Derivation V.S. Structure Derivations do not uniquely represent the structure of the strings
More informationAUTOMATA THEORY AND COMPUTABILITY
AUTOMATA THEORY AND COMPUTABILITY QUESTION BANK Module 1 : Introduction to theory of computation and FSM Objective: Upon the completion of this chapter you will be able to Define Finite automata, Basic
More informationUNIT III & IV. Bottom up parsing
UNIT III & IV Bottom up parsing 5.0 Introduction Given a grammar and a sentence belonging to that grammar, if we have to show that the given sentence belongs to the given grammar, there are two methods.
More informationCOP4020 Programming Languages. Syntax Prof. Robert van Engelen
COP4020 Programming Languages Syntax Prof. Robert van Engelen Overview Tokens and regular expressions Syntax and context-free grammars Grammar derivations More about parse trees Top-down and bottom-up
More informationIntroduction to Parsing. Lecture 5
Introduction to Parsing Lecture 5 1 Outline Regular languages revisited Parser overview Context-free grammars (CFG s) Derivations Ambiguity 2 Languages and Automata Formal languages are very important
More informationNatural Language Processing
Natural Language Processing Anoop Sarkar http://www.cs.sfu.ca/~anoop 9/18/18 1 Ambiguity An input is ambiguous with respect to a CFG if it can be derived with two different parse trees A parser needs a
More informationCOP 3402 Systems Software Top Down Parsing (Recursive Descent)
COP 3402 Systems Software Top Down Parsing (Recursive Descent) Top Down Parsing 1 Outline 1. Top down parsing and LL(k) parsing 2. Recursive descent parsing 3. Example of recursive descent parsing of arithmetic
More informationCS143 Midterm Fall 2008
CS143 Midterm Fall 2008 Please read all instructions (including these) carefully. There are 4 questions on the exam, some with multiple parts. You have 75 minutes to work on the exam. The exam is closed
More informationEDAN65: Compilers, Lecture 06 A LR parsing. Görel Hedin Revised:
EDAN65: Compilers, Lecture 06 A LR parsing Görel Hedin Revised: 2017-09-11 This lecture Regular expressions Context-free grammar Attribute grammar Lexical analyzer (scanner) Syntactic analyzer (parser)
More informationCOMPILER CONSTRUCTION LAB 2 THE SYMBOL TABLE. Tutorial 2 LABS. PHASES OF A COMPILER Source Program. Lab 2 Symbol table
COMPILER CONSTRUCTION Lab 2 Symbol table LABS Lab 3 LR parsing and abstract syntax tree construction using ''bison' Lab 4 Semantic analysis (type checking) PHASES OF A COMPILER Source Program Lab 2 Symtab
More informationCSE 401 Midterm Exam Sample Solution 2/11/15
Question 1. (10 points) Regular expression warmup. For regular expression questions, you must restrict yourself to the basic regular expression operations covered in class and on homework assignments:
More information