Fall Compiler Principles Context-free Grammars Refresher. Roman Manevich Ben-Gurion University of the Negev
|
|
- Georgiana Blake
- 6 years ago
- Views:
Transcription
1 Fall Compiler Principles Context-free Grammars Refresher Roman Manevich Ben-Gurion University of the Negev 1
2 xample grammar S S ; S S id := S print (L) id num + L L L, shorthand for Statement shorthand for xpression shorthand for List (of expressions) 2
3 CFG terminology S S ; S S id := S print (L) id num + L L L, Symbols: Terminals (tokens): ; := ( ) id num print Non-terminals: S L Start non-terminal: S Convention: the non-terminal appearing in the first derivation rule Grammar productions (rules) N α 3
4 More definitions Sentential form: a sequence of symbols, terminals (tokens) and non-terminals Sentence: a sequence of terminals (tokens) Derivation step: given a sentential form αnβ and rule N µ a step is the transition αnβ αµβ Derivation sequence: a sequence of derivation steps 1 k such that i i+1 is the result of applying one production and k is a sentence 4
5 Language of a CFG A word ω is in L(G) (valid program) if there exists a corresponding derivation sequence Start the start symbol Repeatedly replace one of the non-terminals by a right-hand side of a production Stop when the sentence contains only terminals ω is in L(G) if S * ω Leftmost derivation Rightmost derivation 5
6 Leftmost derivation a := 56 ; b := S S ; S S id := S print (L) id num + L L L, S => S ; S => id := ; S => id := num ; S => id := num ; id := => id := num ; id := + => id := num ; id := num + => id := num ; id := num + num id := num ; id := num + num 6
7 Rightmost derivation a := 56 ; b := S S ; S S id := S print (L) id num + L L L, S => S ; S => S ; id := => S ; id := + => S ; id := + num => S ; id := num + num => id := ; id := num + num => id := num ; id := num + num id := num ; id := num + num 7
8 Canonical derivations Leftmost/rightmost derivations may not be unique but they allow describing a derivation by the sequence of production rules taken (since non-terminal is already known) Leftmost derivation example: 1, 2, 5, 2, 6, 5, 5 Rightmost derivation example: 1, 2, 6, 5, 5, 2, 5 8
9 Parse trees Tree nodes are symbols, children ordered left-to-right ach internal node is non-terminal and its children correspond to one of its productions N µ 1 µ k N µ 1 µ k Root is start non-terminal Leaves are tokens Yield of parse tree: left-to-right walk over leaves 9
10 Parse tree exercise S S ; S S id := S print (L) id Draw parse tree for expression num + L L L, id := num ; id := num + num 10
11 Parse tree exercise S S ; S S id := S print (L) id num + L L L, quivalently add parentheses labeled by non-terminal names S S Order-independent representation id := num ; id := num + num ( S ( S a := ( 56) ) S ; ( S b := ( ( 7) + ( 3) ) ) S ) S S 11
12 Capabilities and limitations of CFGs CFGs naturally express Hierarchical structure A program is a list of classes, A Class is a list of definition Alternatives A definition is either a field definition or a method definition Beginning-end type of constraints Balanced parentheses S (S)S ε Cannot express p. 173 Correlations between unbounded strings (identifiers) For example: variables are declared before use: ω S ω Handled by semantic analysis (attribute grammars) 12
13 Badly-formed grammars By Oren neu dag (Own work) [CC-BY-SA-3.0 ( via Wikimedia Commons 13
14 Badly-formed grammars A non-terminal N is reachable if S * αnβ A non-terminal N is generating if N * ω A grammar G is badly-formed if it either contains unreachable nonterminals or non-generating non-terminals G 1 = S x N y G 2 = S x N N a N b N xercise: algorithm to test whether a grammar is badly-formed Theorem: for every grammar G there exists an equivalent wellformed grammar G ( that is, L(G)=L(G ) ) Proof: exercise From now on, we will only handle well-formed grammars 14
15 Ambiguity in Context-free grammars 15
16 Sometimes there are two parse trees Arithmetic expressions: id num 1 + (2 + 3) (1 + 2) * ( ) num(1) + num(2) + num(3) num(1) + num(2) + num(3) Leftmost derivation + num + num + + num + num + num + num + num Rightmost derivation + + num + + num + num + num num + num + num 16
17 Is ambiguity a problem for compilers? Arithmetic expressions: id num 1 + (2 + 3) (1 + 2) Depends on semantics * ( ) num(1) + num(2) + num(3) = 6 num(1) + num(2) + num(3) = 6 Leftmost derivation + num + num + + num + num + num + num + num Rightmost derivation + + num + + num + num + num num + num + num 17
18 Problematic ambiguity example Arithmetic expressions: * 3 id num 1 + (2 * 3) This is what we (1 + 2) * 3 + usually want: * has * precedence over + ( ) num(1) + num(2) * num(3) = 7 num(1) + num(2) * num(3) = 9 Leftmost derivation + num + num + * num + num * num + num * num Rightmost derivation * * num + * num + num * num num + num * num 18
19 Ambiguous grammars A grammar is ambiguous if there exists a word for which there are Two different leftmost derivations Two different rightmost derivations Two different parse trees Property of grammars, not languages 19
20 Facts about ambiguous grammars Some languages are inherently ambiguous no unambiguous grammars exist [Parikh 1961] Checking whether an arbitrary grammar is ambiguous is undecidable [Hopcroft, Motwani, Ullman, 2001] 20
Syntax 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 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 informationMA513: Formal Languages and Automata Theory Topic: Context-free Grammars (CFG) Lecture Number 18 Date: September 12, 2011
MA53: Formal Languages and Automata Theory Topic: Context-free Grammars (CFG) Lecture Number 8 Date: September 2, 20 xercise: Define a context-free grammar that represents (a simplification of) expressions
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 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 informationIntroduction to Parsing. Lecture 5. Professor Alex Aiken Lecture #5 (Modified by Professor Vijay Ganesh)
Introduction to Parsing Lecture 5 (Modified by Professor Vijay Ganesh) 1 Outline Regular languages revisited Parser overview Context-free grammars (CFG s) Derivations Ambiguity 2 Languages and Automata
More informationContext-Free Languages and Parse Trees
Context-Free Languages and Parse Trees Mridul Aanjaneya Stanford University July 12, 2012 Mridul Aanjaneya Automata Theory 1/ 41 Context-Free Grammars A context-free grammar is a notation for describing
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 informationSyntax Analysis Part I
Syntax Analysis Part I Chapter 4: Context-Free Grammars Slides adapted from : Robert van Engelen, Florida State University Position of a Parser in the Compiler Model Source Program Lexical Analyzer Token,
More informationAnnouncements. Written Assignment 1 out, due Friday, July 6th at 5PM.
Syntax Analysis Announcements Written Assignment 1 out, due Friday, July 6th at 5PM. xplore the theoretical aspects of scanning. See the limits of maximal-munch scanning. Class mailing list: There is an
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 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 informationOutline. Regular languages revisited. Introduction to Parsing. Parser overview. Context-free grammars (CFG s) Lecture 5. Derivations.
Outline Regular languages revisited Introduction to Parsing Lecture 5 Parser overview Context-free grammars (CFG s) Derivations Prof. Aiken CS 143 Lecture 5 1 Ambiguity Prof. Aiken CS 143 Lecture 5 2 Languages
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 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 information( ) i 0. Outline. Regular languages revisited. Introduction to Parsing. Parser overview. Context-free grammars (CFG s) Lecture 5.
Outline Regular languages revisited Introduction to Parsing Lecture 5 Parser overview Context-free grammars (CFG s) Derivations Prof. Aiken CS 143 Lecture 5 1 Ambiguity Prof. Aiken CS 143 Lecture 5 2 Languages
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 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 informationParsing: Derivations, Ambiguity, Precedence, Associativity. Lecture 8. Professor Alex Aiken Lecture #5 (Modified by Professor Vijay Ganesh)
Parsing: Derivations, Ambiguity, Precedence, Associativity Lecture 8 (Modified by Professor Vijay Ganesh) 1 Topics covered so far Regular languages and Finite automaton Parser overview Context-free grammars
More informationMore on Syntax. Agenda for the Day. Administrative Stuff. More on Syntax In-Class Exercise Using parse trees
More on Syntax Judy Stafford Comp 80 Meeting February, 00 Agenda for the Day Administrative Stuff Moodle Classlist at without waiting list More on Syntax InClass Exercise Using parse trees Last time Syntax
More informationFall Compiler Principles Lecture 2: LL parsing. Roman Manevich Ben-Gurion University of the Negev
Fall 2017-2018 Compiler Principles Lecture 2: LL parsing Roman Manevich Ben-Gurion University of the Negev 1 Books Compilers Principles, Techniques, and Tools Alfred V. Aho, Ravi Sethi, Jeffrey D. Ullman
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 informationParsing. Roadmap. > Context-free grammars > Derivations and precedence > Top-down parsing > Left-recursion > Look-ahead > Table-driven parsing
Roadmap > Context-free grammars > Derivations and precedence > Top-down parsing > Left-recursion > Look-ahead > Table-driven parsing The role of the parser > performs context-free syntax analysis > guides
More informationCSE302: Compiler Design
CSE302: Compiler Design Instructor: Dr. Liang Cheng Department of Computer Science and Engineering P.C. Rossin College of Engineering & Applied Science Lehigh University February 20, 2007 Outline Recap
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 informationIntroduction to Parsing Ambiguity and Syntax Errors
Introduction to Parsing Ambiguity and Syntax rrors Outline Regular languages revisited Parser overview Context-free grammars (CFG s) Derivations Ambiguity Syntax errors Compiler Design 1 (2011) 2 Languages
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 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 informationAmbiguous Grammars and Compactification
Ambiguous Grammars and Compactification Mridul Aanjaneya Stanford University July 17, 2012 Mridul Aanjaneya Automata Theory 1/ 44 Midterm Review Mathematical Induction and Pigeonhole Principle Finite Automata
More informationIntroduction to Parsing Ambiguity and Syntax Errors
Introduction to Parsing Ambiguity and Syntax rrors Outline Regular languages revisited Parser overview Context-free grammars (CFG s) Derivations Ambiguity Syntax errors 2 Languages and Automata Formal
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 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 informationSyntax Analysis. Prof. James L. Frankel Harvard University. Version of 6:43 PM 6-Feb-2018 Copyright 2018, 2015 James L. Frankel. All rights reserved.
Syntax Analysis Prof. James L. Frankel Harvard University Version of 6:43 PM 6-Feb-2018 Copyright 2018, 2015 James L. Frankel. All rights reserved. Context-Free Grammar (CFG) terminals non-terminals start
More informationMIT Specifying Languages with Regular Expressions and Context-Free Grammars
MIT 6.035 Specifying Languages with Regular essions and Context-Free Grammars Martin Rinard Laboratory for Computer Science Massachusetts Institute of Technology Language Definition Problem How to precisely
More informationFall Compiler Principles Lecture 2: LL parsing. Roman Manevich Ben-Gurion University of the Negev
Fall 2016-2017 Compiler Principles Lecture 2: LL parsing Roman Manevich Ben-Gurion University of the Negev 1 Books Compilers Principles, Techniques, and Tools Alfred V. Aho, Ravi Sethi, Jeffrey D. Ullman
More informationOptimizing Finite Automata
Optimizing Finite Automata We can improve the DFA created by MakeDeterministic. Sometimes a DFA will have more states than necessary. For every DFA there is a unique smallest equivalent DFA (fewest states
More informationAmbiguity, Precedence, Associativity & Top-Down Parsing. Lecture 9-10
Ambiguity, Precedence, Associativity & Top-Down Parsing Lecture 9-10 (From slides by G. Necula & R. Bodik) 9/18/06 Prof. Hilfinger CS164 Lecture 9 1 Administrivia Please let me know if there are continued
More information3. Parsing. Oscar Nierstrasz
3. Parsing Oscar Nierstrasz Thanks to Jens Palsberg and Tony Hosking for their kind permission to reuse and adapt the CS132 and CS502 lecture notes. http://www.cs.ucla.edu/~palsberg/ http://www.cs.purdue.edu/homes/hosking/
More informationGrammars and ambiguity. CS164 3:30-5:00 TT 10 Evans. Prof. Bodik CS 164 Lecture 8 1
Grammars and ambiguity CS164 3:30-5:00 TT 10 vans 1 Overview derivations and parse trees different derivations produce may produce same parse tree ambiguous grammars what they are and how to fix them 2
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 informationContext-Free Grammars
CFG2: Ambiguity Context-Free Grammars CMPT 379: Compilers Instructor: Anoop Sarkar anoopsarkar.github.io/compilers-class Ambiguity - / - / ( ) - / / - 16-06-22 2 Ambiguity Grammar is ambiguous if more
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 informationIntro To Parsing. Step By Step
#1 Intro To Parsing Step By Step #2 Self-Test from Last Time Are practical parsers and scanners based on deterministic or non-deterministic automata? How can regular expressions be used to specify nested
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 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 information([1-9] 1[0-2]):[0-5][0-9](AM PM)? What does the above match? Matches clock time, may or may not be told if it is AM or PM.
What is the corresponding regex? [2-9]: ([1-9] 1[0-2]):[0-5][0-9](AM PM)? What does the above match? Matches clock time, may or may not be told if it is AM or PM. CS 230 - Spring 2018 4-1 More CFG Notation
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 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 informationSometimes an ambiguous grammar can be rewritten to eliminate the ambiguity.
Eliminating Ambiguity Sometimes an ambiguous grammar can be rewritten to eliminate the ambiguity. Example: consider the following grammar stat if expr then stat if expr then stat else stat other One can
More informationLecture 8: Context Free Grammars
Lecture 8: Context Free s Dr Kieran T. Herley Department of Computer Science University College Cork 2017-2018 KH (12/10/17) Lecture 8: Context Free s 2017-2018 1 / 1 Specifying Non-Regular Languages Recall
More informationDescribing Syntax and Semantics
Describing Syntax and Semantics Introduction Syntax: the form or structure of the expressions, statements, and program units Semantics: the meaning of the expressions, statements, and program units Syntax
More informationSYNTAX ANALYSIS 1. Define parser. Hierarchical analysis is one in which the tokens are grouped hierarchically into nested collections with collective meaning. Also termed as Parsing. 2. Mention the basic
More informationMIT Specifying Languages with Regular Expressions and Context-Free Grammars. Martin Rinard Massachusetts Institute of Technology
MIT 6.035 Specifying Languages with Regular essions and Context-Free Grammars Martin Rinard Massachusetts Institute of Technology Language Definition Problem How to precisely define language Layered structure
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 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 informationFall Compiler Principles Lecture 3: Parsing part 2. Roman Manevich Ben-Gurion University
Fall 2014-2015 Compiler Principles Lecture 3: Parsing part 2 Roman Manevich Ben-Gurion University Tentative syllabus Front End Intermediate Representation Optimizations Code Generation Scanning Lowering
More informationOutline. Limitations of regular languages Parser overview Context-free grammars (CFG s) Derivations Syntax-Directed Translation
Outline Introduction to Parsing Lecture 8 Adapted from slides by G. Necula and R. Bodik Limitations of regular languages Parser overview Context-free grammars (CG s) Derivations Syntax-Directed ranslation
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 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 informationCMPS Programming Languages. Dr. Chengwei Lei CEECS California State University, Bakersfield
CMPS 3500 Programming Languages Dr. Chengwei Lei CEECS California State University, Bakersfield Chapter 3 Describing Syntax and Semantics Chapter 3 Topics Introduction The General Problem of Describing
More informationprogramming languages need to be precise a regular expression is one of the following: tokens are the building blocks of programs
Chapter 2 :: Programming Language Syntax Programming Language Pragmatics Michael L. Scott Introduction programming languages need to be precise natural languages less so both form (syntax) and meaning
More informationE E+E E E (E) id. id + id E E+E. id E + E id id + E id id + id. Overview. derivations and parse trees. Grammars and ambiguity. ambiguous grammars
Overview Grammars and ambiguity CS164 3:30-5:00 TT 10 vans derivations and parse trees dferent derivations produce may produce same parse tree ambiguous grammars what they are and how to fix them 1 2 Recall:
More informationParsing Part II. (Ambiguity, Top-down parsing, Left-recursion Removal)
Parsing Part II (Ambiguity, Top-down parsing, Left-recursion Removal) Ambiguous Grammars Definitions If a grammar has more than one leftmost derivation for a single sentential form, the grammar is ambiguous
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 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 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 informationThe analysis part breaks up the source program into constituent pieces and creates an intermediate representation of the source program.
COMPILER DESIGN 1. What is a compiler? A compiler is a program that reads a program written in one language the source language and translates it into an equivalent program in another language-the target
More informationParsing III. CS434 Lecture 8 Spring 2005 Department of Computer Science University of Alabama Joel Jones
Parsing III (Top-down parsing: recursive descent & LL(1) ) (Bottom-up parsing) CS434 Lecture 8 Spring 2005 Department of Computer Science University of Alabama Joel Jones Copyright 2003, Keith D. Cooper,
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 informationDefining syntax using CFGs
Defining syntax using CFGs Roadmap Last time Defined context-free grammar This time CFGs for specifying a language s syntax Language membership List grammars Resolving ambiguity CFG Review G = (N,Σ,P,S)
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 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 informationProperties of Regular Expressions and Finite Automata
Properties of Regular Expressions and Finite Automata Some token patterns can t be defined as regular expressions or finite automata. Consider the set of balanced brackets of the form [[[ ]]]. This set
More informationSyntax Analysis. Amitabha Sanyal. (www.cse.iitb.ac.in/ as) Department of Computer Science and Engineering, Indian Institute of Technology, Bombay
Syntax Analysis (www.cse.iitb.ac.in/ as) Department of Computer Science and Engineering, Indian Institute of Technology, Bombay September 2007 College of Engineering, Pune Syntax Analysis: 2/124 Syntax
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 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 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 informationChapter 4. Syntax - the form or structure of the expressions, statements, and program units
Syntax - the form or structure of the expressions, statements, and program units Semantics - the meaning of the expressions, statements, and program units Who must use language definitions? 1. Other language
More informationCompilers Course Lecture 4: Context Free Grammars
Compilers Course Lecture 4: Context Free Grammars Example: attempt to define simple arithmetic expressions using named regular expressions: num = [0-9]+ sum = expr "+" expr expr = "(" sum ")" num Appears
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 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 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 informationGrammars & Parsing. Lecture 12 CS 2112 Fall 2018
Grammars & Parsing Lecture 12 CS 2112 Fall 2018 Motivation The cat ate the rat. The cat ate the rat slowly. The small cat ate the big rat slowly. The small cat ate the big rat on the mat slowly. The small
More informationCS153: Compilers Lecture 4: Recursive Parsing
CS153: Compilers Lecture 4: Recursive Parsing Stephen Chong https://www.seas.harvard.edu/courses/cs153 Announcements Proj 1 out Due Thursday Sept 20 11:59 Start soon if you haven t! Proj 2 released today
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 Context-Free Grammars A grammar G=(V, T, S, P) is context-free if all productions in P are of form A
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 informationVIVA QUESTIONS WITH ANSWERS
VIVA QUESTIONS WITH ANSWERS 1. What is a compiler? A compiler is a program that reads a program written in one language the source language and translates it into an equivalent program in another language-the
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 informationCSE P 501 Compilers. Parsing & Context-Free Grammars Hal Perkins Winter /15/ Hal Perkins & UW CSE C-1
CSE P 501 Compilers Parsing & Context-Free Grammars Hal Perkins Winter 2008 1/15/2008 2002-08 Hal Perkins & UW CSE C-1 Agenda for Today Parsing overview Context free grammars Ambiguous grammars Reading:
More informationEDA180: Compiler Construc6on Context- free grammars. Görel Hedin Revised:
EDA180: Compiler Construc6on Context- free grammars Görel Hedin Revised: 2013-01- 28 Compiler phases and program representa6ons source code Lexical analysis (scanning) Intermediate code genera6on tokens
More informationEng. Maha Talaat Page 1
El-Shorouk cademy cad. Year : 2013 / 2014 Higher Institute for Computer & Term : 2nd Information Technology Year : 4th Computer Science Department Supervisor: Prof. Dr. hmed bbassy Section contents: mbiguity
More informationDefinition: two derivations are similar if one of them precedes the other.
Parse Trees and Ambiguity (Chapter 3, ection 3.2) Cmc 365 Theory of Computation 1. Derivations and similarity Let G be a CFG. A string w L(G) may have many derivations, corresponding to how we choose the
More informationAmbiguity. Grammar E E + E E * E ( E ) int. The string int * int + int has two parse trees. * int
Administrivia Ambiguity, Precedence, Associativity & op-down Parsing eam assignments this evening for all those not listed as having one. HW#3 is now available, due next uesday morning (Monday is a holiday).
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 information2.2 Syntax Definition
42 CHAPTER 2. A SIMPLE SYNTAX-DIRECTED TRANSLATOR sequence of "three-address" instructions; a more complete example appears in Fig. 2.2. This form of intermediate code takes its name from instructions
More informationTHE COMPILATION PROCESS EXAMPLE OF TOKENS AND ATTRIBUTES
THE COMPILATION PROCESS Character stream CS 403: Scanning and Parsing Stefan D. Bruda Fall 207 Token stream Parse tree Abstract syntax tree Modified intermediate form Target language Modified target language
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 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 informationIntroduction to Lexing and Parsing
Introduction to Lexing and Parsing ECE 351: Compilers Jon Eyolfson University of Waterloo June 18, 2012 1 Riddle Me This, Riddle Me That What is a compiler? 1 Riddle Me This, Riddle Me That What is a compiler?
More information