Edited by Himanshu Mittal. Lexical Analysis Phase
|
|
- Sheryl Owen
- 6 years ago
- Views:
Transcription
1 Edited by Himanshu Mittal Lexical Analysis Phase
2 Lexical Analyzer The main task of Lexical analysis is to read input characters of source program and group them into lexemes and produce as output a sequence of tokens for each lexeme in the source file. Other tasks: Stripping out comments and whitespaces Co-relating error messages.
3 Role of Lexical Analyzer Parser issues getnexttoken command that causes the lexical analyzer to read input characters until it can identify the next lexeme and produce it as next token which it returns to parser. The stream of tokens is sent to the parser for syntax analysis.
4 Patterns Pattern: The definition used for recognizing tokens. Regular expressions are used for defining/specifying patterns. NFA/DFA is used to implement the regular expressions.
5 Lexeme Lexeme: A sequence of characters (or substring) in the input, identified by a pattern(or regular expression) as token. Eg., in a C stmt, int a = 0 Lexemes are int, a, =, 0.
6 Token Class Token Class: A category to which a lexeme can belong. Some common token class are Keyword, Identifier, Digit, Operator, Literals. Eg., in C stmt, int a = 0: int belongs to keyword class, a belongs to identifier class, = belongs to operator class, 0 belongs to digit class.
7 Another Example In C stmt, char v= hello //v is a variable char belongs to keyword class, v belongs to identifier class, = belongs to operator class, hello belongs to literal class, //v is a variable belongs to comment class.
8 Token Token: Symbol used for representing lexeme. The representation form for tokens can vary. Generally, tokens are represented as pair of token class and lexeme. <token_class,lexeme> Eg., token of int is <keyword,int>. Note: Patterns for tokens are specified through regular expression. Recognition of token is done through finite automata(nfa/dfa).
9 Lex Tool Tool for constructing lexical analyzers from special purpose notations based on regular expressions. Tool widely used to specify lexical analyzers for a variety of languages. Free available with Unix Terminal
10 Lex Tool Lex program is a file with extension.l that contains regular expressions, together with the actions to be taken when each expression is matched. Lex compiler produces an output file, usually called lex.yy.c, that contains C code defining a procedure yylex() which is table driven implementation of a DFA corresponding to the regular expression in the lex file and that operates like a gettoken procedure. The lex.yy.c file is then compiled and linked to a main program to get a running program using C compiler.
11 Lex Process Create a file, named as filename.l, that contains specifications/regular expression. lex compiler processes filename.l and produces lex.yy.c file. The C compiler turns lex.yy.c file into a.out file. Steps to execute a lex file on unix terminal: lex filename.l gcc lex.yy.c ll (-ll means link with lex library, use lfl if using flex)./a.out Note: lex contains a function yylex( ) which does actual lexical analysis.
12 Creating a Lexical Analyzer with LEX Lex source program LEX Compiler Lex.yy.c Lex.yy.c C Compiler a.out Input Stream a.out Sequence of tokens
13 Lex File Format <Definitions> %% <Rules> %% <Supplementary code> #includes #defines RegExps Pattern/Action Pairs {pattern1} {action1} {pattern2} {action2} Additional code (Not always needed)
14 Eg: Simple Lex Program Small program Lex program that prints everything as output that is entered as input. File Name: scan.l %%. \n %% main() { } yylex(); ECHO; We get this by default in Lex! This form will read from stdin. To terminate type: ctrl/d Put this code in a file called: scan.l Run lex: lex scan.l Compile: gcc lex.yy.c -ll Run by typing:./a.out or a.out < somefile.txt
15 Another Example %{ #include<stdio.h> %} digit [0-9]+ letter [a-za-z]+ How to include c code id {letter}({letter} {digit})* %% {id} { printf( Found identifier %s,yytext); } {digit} {printf( Found Digit %s,yytext); } %% yytext is an Internal variable containing text of word matched
16 Eg: To count of variables in input string %{ #include<stdio.h> int count=0; %} digit [0-9]+ letter [a-za-z]+ id {letter}({letter} {digit})* %% {id} { count++ } %% int main() { yylex(); printf( The no. of variables in string: %d,count); return(0); }
17 Main Points Text that is not matched is echoed as read. Thus, there is an implied ECHO. If you don't specifiy a main you get one for free!!! Lex patterns only match a given input character or string once Lex executes the action for the longest possible match for the current input. If two patterns are of same length, then lex executes the action of pattern that has high priority(or first in pattern sequence).
18 Example: AAA { printf("<found 3 A's>"); } AA { printf("<found 2 A's>"); } Given Input: AAAAAAAA Will print: <Found 3 A's><Found 3 A's><Found 2 A's> The scanning continues unless a value is returned!
19 Lex Predefined Variables yytext --> a string containing the matched lexeme yyleng --> the length of the matched lexeme yyin --> the input stream pointer the default input of default main() is stdin yyout --> the output stream pointer the default output of default main() is stdout. E.g.,./a.out < inputfile > outfile E.g. [a-z]+ [a-z]+ [a-za-z]+ printf( %s, yytext); ECHO; {words++; chars += yyleng;} PLLab, NTHU,Cs2403 Programming Languages 19
20 Lex Library Routines yylex() The default main() contains a call of yylex() yymore() return the next token yyless(n) retain the first n characters in yytext yywarp() is called whenever Lex reaches an end-of-file The default yywarp() always returns 1 PLLab, NTHU,Cs2403 Programming Languages 20
21 Pattern Matching Primitives Metacharacter Matches. any character except newline \n newline * zero or more copies of the preceding expression + one or more copies of the preceding expression? zero or one copy of the preceding expression ^ beginning of line / complement $ end of line a b a or b (ab)+ one or more copies of ab (grouping) [ab] a or b a{3} 3 instances of a a+b literal a+b (C escapes still work)
22 Review of Lex Predefined Variables Name char *yytext int yyleng FILE *yyin FILE *yyout int yylex(void) char* yymore(void) int yyless(int n) int yywrap(void) ECHO REJECT INITAL BEGIN Function pointer to matched string length of matched string input stream pointer output stream pointer call to invoke lexer, returns token return the next token retain the first n characters in yytext wrapup, return 1 if done, 0 if not done write matched string go to the next alternative rule initial start condition condition switch start condition
Module 8 - Lexical Analyzer Generator. 8.1 Need for a Tool. 8.2 Lexical Analyzer Generator Tool
Module 8 - Lexical Analyzer Generator This module discusses the core issues in designing a lexical analyzer generator from basis or using a tool. The basics of LEX tool are also discussed. 8.1 Need for
More informationEXPERIMENT NO : M/C Lenovo Think center M700 Ci3,6100,6th Gen. H81, 4GB RAM,500GB HDD
GROUP - B EXPERIMENT NO : 07 1. Title: Write a program using Lex specifications to implement lexical analysis phase of compiler to total nos of words, chars and line etc of given file. 2. Objectives :
More informationUsing Lex or Flex. Prof. James L. Frankel Harvard University
Using Lex or Flex Prof. James L. Frankel Harvard University Version of 1:07 PM 26-Sep-2016 Copyright 2016, 2015 James L. Frankel. All rights reserved. Lex Regular Expressions (1 of 4) Special characters
More informationEXPERIMENT NO : M/C Lenovo Think center M700 Ci3,6100,6th Gen. H81, 4GB RAM,500GB HDD
GROUP - B EXPERIMENT NO : 06 1. Title: Write a program using Lex specifications to implement lexical analysis phase of compiler to generate tokens of subset of Java program 2. Objectives : - To understand
More informationLexical Analysis. Implementing Scanners & LEX: A Lexical Analyzer Tool
Lexical Analysis Implementing Scanners & LEX: A Lexical Analyzer Tool Copyright 2016, Pedro C. Diniz, all rights reserved. Students enrolled in the Compilers class at the University of Southern California
More informationCS4850 SummerII Lex Primer. Usage Paradigm of Lex. Lex is a tool for creating lexical analyzers. Lexical analyzers tokenize input streams.
CS4850 SummerII 2006 Lexical Analysis and Lex (contd) 4.1 Lex Primer Lex is a tool for creating lexical analyzers. Lexical analyzers tokenize input streams. Tokens are the terminals of a language. Regular
More informationLecture Outline. COMP-421 Compiler Design. What is Lex? Lex Specification. ! Lexical Analyzer Lex. ! Lex Examples. Presented by Dr Ioanna Dionysiou
Lecture Outline COMP-421 Compiler Design! Lexical Analyzer Lex! Lex Examples Presented by Dr Ioanna Dionysiou Figures and part of the lecture notes taken from A compact guide to lex&yacc, epaperpress.com
More informationBig Picture: Compilation Process. CSCI: 4500/6500 Programming Languages. Big Picture: Compilation Process. Big Picture: Compilation Process.
Big Picture: Compilation Process Source program CSCI: 4500/6500 Programming Languages Lex & Yacc Scanner Lexical Lexical units, token stream Parser Syntax Intermediate Parse tree Code Generator Semantic
More informationFigure 2.1: Role of Lexical Analyzer
Chapter 2 Lexical Analysis Lexical analysis or scanning is the process which reads the stream of characters making up the source program from left-to-right and groups them into tokens. The lexical analyzer
More informationLEX/Flex Scanner Generator
Compiler Design 1 LEX/Flex Scanner Generator Compiler Design 2 flex - Fast Lexical Analyzer Generator We can use flex a to automatically generate the lexical analyzer/scanner for the lexical atoms of a
More informationAn introduction to Flex
An introduction to Flex 1 Introduction 1.1 What is Flex? Flex takes a set of descriptions of possible tokens and produces a scanner. 1.2 A short history Lex was developed at Bell Laboratories in the 1970s.
More informationThe structure of a compiler
The structure of a compiler Source code front-end Intermediate front-end representation compiler back-end machine code Front-end & Back-end C front-end Pascal front-end C front-end Intel x86 back-end Motorola
More informationCSC 467 Lecture 3: Regular Expressions
CSC 467 Lecture 3: Regular Expressions Recall How we build a lexer by hand o Use fgetc/mmap to read input o Use a big switch to match patterns Homework exercise static TokenKind identifier( TokenKind token
More informationBig Picture: Compilation Process. CSCI: 4500/6500 Programming Languages. Big Picture: Compilation Process. Big Picture: Compilation Process
Big Picture: Compilation Process Source program CSCI: 4500/6500 Programming Languages Lex & Yacc Symbol Table Scanner Lexical Parser Syntax Intermediate Code Generator Semantic Lexical units, token stream
More informationProf. Mohamed Hamada Software Engineering Lab. The University of Aizu Japan
Compilers Prof. Mohamed Hamada Software Engineering Lab. The University of Aizu Japan Lexical Analyzer (Scanner) 1. Uses Regular Expressions to define tokens 2. Uses Finite Automata to recognize tokens
More informationLexical and Syntax Analysis
Lexical and Syntax Analysis (of Programming Languages) Flex, a Lexical Analyser Generator Lexical and Syntax Analysis (of Programming Languages) Flex, a Lexical Analyser Generator Flex: a fast lexical
More informationCS143 Handout 04 Summer 2011 June 22, 2011 flex In A Nutshell
CS143 Handout 04 Summer 2011 June 22, 2011 flex In A Nutshell Handout written by Julie Zelenski with minor edits by Keith. flex is a fast lexical analyzer generator. You specify the scanner you want in
More informationPRINCIPLES OF COMPILER DESIGN UNIT II LEXICAL ANALYSIS 2.1 Lexical Analysis - The Role of the Lexical Analyzer
PRINCIPLES OF COMPILER DESIGN UNIT II LEXICAL ANALYSIS 2.1 Lexical Analysis - The Role of the Lexical Analyzer As the first phase of a compiler, the main task of the lexical analyzer is to read the input
More informationConcepts Introduced in Chapter 3. Lexical Analysis. Lexical Analysis Terms. Attributes for Tokens
Concepts Introduced in Chapter 3 Lexical Analysis Regular Expressions (REs) Nondeterministic Finite Automata (NFA) Converting an RE to an NFA Deterministic Finite Automatic (DFA) Lexical Analysis Why separate
More informationFlex and lexical analysis
Flex and lexical analysis From the area of compilers, we get a host of tools to convert text files into programs. The first part of that process is often called lexical analysis, particularly for such
More informationChapter 3 Lexical Analysis
Chapter 3 Lexical Analysis Outline Role of lexical analyzer Specification of tokens Recognition of tokens Lexical analyzer generator Finite automata Design of lexical analyzer generator The role of lexical
More informationCompiler course. Chapter 3 Lexical Analysis
Compiler course Chapter 3 Lexical Analysis 1 A. A. Pourhaji Kazem, Spring 2009 Outline Role of lexical analyzer Specification of tokens Recognition of tokens Lexical analyzer generator Finite automata
More informationAn Introduction to LEX and YACC. SYSC Programming Languages
An Introduction to LEX and YACC SYSC-3101 1 Programming Languages CONTENTS CONTENTS Contents 1 General Structure 3 2 Lex - A lexical analyzer 4 3 Yacc - Yet another compiler compiler 10 4 Main Program
More informationFlex and lexical analysis. October 25, 2016
Flex and lexical analysis October 25, 2016 Flex and lexical analysis From the area of compilers, we get a host of tools to convert text files into programs. The first part of that process is often called
More informationLexical analysis. Syntactical analysis. Semantical analysis. Intermediate code generation. Optimization. Code generation. Target specific optimization
Second round: the scanner Lexical analysis Syntactical analysis Semantical analysis Intermediate code generation Optimization Code generation Target specific optimization Lexical analysis (Chapter 3) Why
More informationTDDD55- Compilers and Interpreters Lesson 2
TDDD55- Compilers and Interpreters Lesson 2 November 11 2011 Kristian Stavåker (kristian.stavaker@liu.se) Department of Computer and Information Science Linköping University PURPOSE OF LESSONS The purpose
More informationMarcello Bersani Ed. 22, via Golgi 42, 3 piano 3769
Marcello Bersani bersani@elet.polimi.it http://home.dei.polimi.it/bersani/ Ed. 22, via Golgi 42, 3 piano 3769 Flex, Bison and the ACSE compiler suite Marcello M. Bersani LFC Politecnico di Milano Schedule
More informationChapter 4. Lexical analysis. Concepts. Lexical scanning Regular expressions DFAs and FSAs Lex. Lexical analysis in perspective
Chapter 4 Lexical analysis Lexical scanning Regular expressions DFAs and FSAs Lex Concepts CMSC 331, Some material 1998 by Addison Wesley Longman, Inc. 1 CMSC 331, Some material 1998 by Addison Wesley
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 13, 2007 Outline Recap
More informationLECTURE 6 Scanning Part 2
LECTURE 6 Scanning Part 2 FROM DFA TO SCANNER In the previous lectures, we discussed how one might specify valid tokens in a language using regular expressions. We then discussed how we can create a recognizer
More informationType 3 languages. Regular grammars Finite automata. Regular expressions. Deterministic Nondeterministic. a, a, ε, E 1.E 2, E 1 E 2, E 1*, (E 1 )
Course 7 1 Type 3 languages Regular grammars Finite automata Deterministic Nondeterministic Regular expressions a, a, ε, E 1.E 2, E 1 E 2, E 1*, (E 1 ) 2 Brief history of programming Stages of compilation
More informationConcepts. Lexical scanning Regular expressions DFAs and FSAs Lex. Lexical analysis in perspective
Concepts Lexical scanning Regular expressions DFAs and FSAs Lex CMSC 331, Some material 1998 by Addison Wesley Longman, Inc. 1 CMSC 331, Some material 1998 by Addison Wesley Longman, Inc. 2 Lexical analysis
More informationPreparing for the ACW Languages & Compilers
Preparing for the ACW 08348 Languages & Compilers Introductory Lab There is an Introductory Lab Just involves copying the lab task See separate Lab slides Language Roadmaps Convenient way of showing syntax
More informationProgram Development Tools. Lexical Analyzers. Lexical Analysis Terms. Attributes for Tokens
Program Development Tools lex makefiles vi and gvim ctags source level debugging diff and cmp Lexical Analyzers A lexical analyzer reads in a stream of characters as input and produces a sequence of symbols
More informationLexical Analyzer Scanner
Lexical Analyzer Scanner ASU Textbook Chapter 3.1, 3.3, 3.4, 3.6, 3.7, 3.5 Tsan-sheng Hsu tshsu@iis.sinica.edu.tw http://www.iis.sinica.edu.tw/~tshsu 1 Main tasks Read the input characters and produce
More informationLexical Analyzer Scanner
Lexical Analyzer Scanner ASU Textbook Chapter 3.1, 3.3, 3.4, 3.6, 3.7, 3.5 Tsan-sheng Hsu tshsu@iis.sinica.edu.tw http://www.iis.sinica.edu.tw/~tshsu 1 Main tasks Read the input characters and produce
More informationLexical and Parser Tools
Lexical and Parser Tools CSE 413, Autumn 2005 Programming Languages http://www.cs.washington.edu/education/courses/413/05au/ 7-Dec-2005 cse413-20-tools 2005 University of Washington 1 References» The Lex
More informationParsing and Pattern Recognition
Topics in IT 1 Parsing and Pattern Recognition Week 10 Lexical analysis College of Information Science and Engineering Ritsumeikan University 1 this week mid-term evaluation review lexical analysis its
More informationHandout 7, Lex (5/30/2001)
Handout 7, Lex (5/30/2001) Lex is a venerable Unix tool that generates scanners. Input to lex is a text file that specifies the scanner; more precisely: specifying tokens, a yet to be made scanner must
More informationIntroduction to Lex & Yacc. (flex & bison)
Introduction to Lex & Yacc (flex & bison) Lex & Yacc (flex & bison) lexical rules (regular expression) lexical rules (context-free grammar) lex (flex) yacc (bison) Input yylex() yyparse() Processed output
More informationLex & Yacc (GNU distribution - flex & bison) Jeonghwan Park
Lex & Yacc (GNU distribution - flex & bison) Jeonghwan Park Prerequisite Ubuntu Version 14.04 or over Virtual machine for Windows user or native OS flex bison gcc Version 4.7 or over Install in Ubuntu
More informationChapter 3 -- Scanner (Lexical Analyzer)
Chapter 3 -- Scanner (Lexical Analyzer) Job: Translate input character stream into a token stream (terminals) Most programs with structured input have to deal with this problem Need precise definition
More informationFormal Languages and Compilers Lecture VI: Lexical Analysis
Formal Languages and Compilers Lecture VI: Lexical Analysis Free University of Bozen-Bolzano Faculty of Computer Science POS Building, Room: 2.03 artale@inf.unibz.it http://www.inf.unibz.it/ artale/ Formal
More informationPRACTICAL CLASS: Flex & Bison
Master s Degree Course in Computer Engineering Formal Languages FORMAL LANGUAGES AND COMPILERS PRACTICAL CLASS: Flex & Bison Eliana Bove eliana.bove@poliba.it Install On Linux: install with the package
More informationImplementation of Lexical Analysis
Implementation of Lexical Analysis Outline Specifying lexical structure using regular expressions Finite automata Deterministic Finite Automata (DFAs) Non-deterministic Finite Automata (NFAs) Implementation
More informationScanning. COMP 520: Compiler Design (4 credits) Professor Laurie Hendren.
COMP 520 Winter 2016 Scanning COMP 520: Compiler Design (4 credits) Professor Laurie Hendren hendren@cs.mcgill.ca Scanning (1) COMP 520 Winter 2016 Scanning (2) Readings Crafting a Compiler: Chapter 2,
More informationLex (Lesk & Schmidt[Lesk75]) was developed in the early to mid- 70 s.
Lex (October 17, 2003) 1 1 Lexical Analysis What is Lexical Analysis? Process of breaking input into tokens. Sometimes called scanning or tokenizing. Lexical Analyzer scans the input stream and converts
More informationScanning. COMP 520: Compiler Design (4 credits) Alexander Krolik MWF 13:30-14:30, MD 279
COMP 520 Winter 2017 Scanning COMP 520: Compiler Design (4 credits) Alexander Krolik alexander.krolik@mail.mcgill.ca MWF 13:30-14:30, MD 279 Scanning (1) COMP 520 Winter 2017 Scanning (2) Announcements
More informationA program that performs lexical analysis may be termed a lexer, tokenizer, or scanner, though scanner is also a term for the first stage of a lexer.
Compiler Design A compiler is computer software that transforms computer code written in one programming language (the source language) into another programming language (the target language). The name
More informationLexical Analysis. Lecture 3. January 10, 2018
Lexical Analysis Lecture 3 January 10, 2018 Announcements PA1c due tonight at 11:50pm! Don t forget about PA1, the Cool implementation! Use Monday s lecture, the video guides and Cool examples if you re
More informationAutomatic Scanning and Parsing using LEX and YACC
Available Online at www.ijcsmc.com International Journal of Computer Science and Mobile Computing A Monthly Journal of Computer Science and Information Technology ISSN 2320 088X IMPACT FACTOR: 6.017 IJCSMC,
More informationScanners. Xiaokang Qiu Purdue University. August 24, ECE 468 Adapted from Kulkarni 2012
Scanners Xiaokang Qiu Purdue University ECE 468 Adapted from Kulkarni 2012 August 24, 2016 Scanners Sometimes called lexers Recall: scanners break input stream up into a set of tokens Identifiers, reserved
More informationImplementation of Lexical Analysis
Implementation of Lexical Analysis Outline Specifying lexical structure using regular expressions Finite automata Deterministic Finite Automata (DFAs) Non-deterministic Finite Automata (NFAs) Implementation
More informationLex & Yacc. By H. Altay Güvenir. A compiler or an interpreter performs its task in 3 stages:
Lex & Yacc By H. Altay Güvenir A compiler or an interpreter performs its task in 3 stages: 1) Lexical Analysis: Lexical analyzer: scans the input stream and converts sequences of characters into tokens.
More informationLexical Analysis. Chapter 1, Section Chapter 3, Section 3.1, 3.3, 3.4, 3.5 JFlex Manual
Lexical Analysis Chapter 1, Section 1.2.1 Chapter 3, Section 3.1, 3.3, 3.4, 3.5 JFlex Manual Inside the Compiler: Front End Lexical analyzer (aka scanner) Converts ASCII or Unicode to a stream of tokens
More information2 Input and Output The input of your program is any file with text. The output of your program will be a description of the strings that the program r
CSCI 2400 Models of Computation Project 1: Lex Return Day: Tuesday, October 23. Teams: You must form teams of 2 or 3 persons. 1 Overview In this assignment you will use the lexical analyzer lex to write
More informationLexical Analysis. Sukree Sinthupinyo July Chulalongkorn University
Sukree Sinthupinyo 1 1 Department of Computer Engineering Chulalongkorn University 14 July 2012 Outline Introduction 1 Introduction 2 3 4 Transition Diagrams Learning Objectives Understand definition of
More informationIntroduction to Lexical Analysis
Introduction to Lexical Analysis Outline Informal sketch of lexical analysis Identifies tokens in input string Issues in lexical analysis Lookahead Ambiguities Specifying lexical analyzers (lexers) Regular
More informationLex & Yacc. by H. Altay Güvenir. A compiler or an interpreter performs its task in 3 stages:
Lex & Yacc by H. Altay Güvenir A compiler or an interpreter performs its task in 3 stages: 1) Lexical Analysis: Lexical analyzer: scans the input stream and converts sequences of characters into tokens.
More informationIntroduction to Lexical Analysis
Introduction to Lexical Analysis Outline Informal sketch of lexical analysis Identifies tokens in input string Issues in lexical analysis Lookahead Ambiguities Specifying lexers Regular expressions Examples
More informationLexical Analysis. Dragon Book Chapter 3 Formal Languages Regular Expressions Finite Automata Theory Lexical Analysis using Automata
Lexical Analysis Dragon Book Chapter 3 Formal Languages Regular Expressions Finite Automata Theory Lexical Analysis using Automata Phase Ordering of Front-Ends Lexical analysis (lexer) Break input string
More informationLECTURE 7. Lex and Intro to Parsing
LECTURE 7 Lex and Intro to Parsing LEX Last lecture, we learned a little bit about how we can take our regular expressions (which specify our valid tokens) and create real programs that can recognize them.
More informationMonday, August 26, 13. Scanners
Scanners Scanners Sometimes called lexers Recall: scanners break input stream up into a set of tokens Identifiers, reserved words, literals, etc. What do we need to know? How do we define tokens? How can
More informationWednesday, September 3, 14. Scanners
Scanners Scanners Sometimes called lexers Recall: scanners break input stream up into a set of tokens Identifiers, reserved words, literals, etc. What do we need to know? How do we define tokens? How can
More informationCOLLEGE OF ENGINEERING, NASHIK. LANGUAGE TRANSLATOR
Pune Vidyarthi Griha s COLLEGE OF ENGINEERING, NASHIK. LANGUAGE TRANSLATOR By Prof. Anand N. Gharu (Assistant Professor) PVGCOE Computer Dept.. 22nd Jan 2018 CONTENTS :- 1. Role of lexical analysis 2.
More informationStructure of Programming Languages Lecture 3
Structure of Programming Languages Lecture 3 CSCI 6636 4536 Spring 2017 CSCI 6636 4536 Lecture 3... 1/25 Spring 2017 1 / 25 Outline 1 Finite Languages Deterministic Finite State Machines Lexical Analysis
More informationThe Language for Specifying Lexical Analyzer
The Language for Specifying Lexical Analyzer We shall now study how to build a lexical analyzer from a specification of tokens in the form of a list of regular expressions The discussion centers around
More informationCOMPILER DESIGN UNIT I LEXICAL ANALYSIS. Translator: It is a program that translates one language to another Language.
UNIT I LEXICAL ANALYSIS Translator: It is a program that translates one language to another Language. Source Code Translator Target Code 1. INTRODUCTION TO LANGUAGE PROCESSING The Language Processing System
More informationLECTURE 11. Semantic Analysis and Yacc
LECTURE 11 Semantic Analysis and Yacc REVIEW OF LAST LECTURE In the last lecture, we introduced the basic idea behind semantic analysis. Instead of merely specifying valid structures with a context-free
More informationflex is not a bad tool to use for doing modest text transformations and for programs that collect statistics on input.
flex is not a bad tool to use for doing modest text transformations and for programs that collect statistics on input. More often than not, though, you ll want to use flex to generate a scanner that divides
More informationSyntactic Analysis. CS345H: Programming Languages. Lecture 3: Lexical Analysis. Outline. Lexical Analysis. What is a Token? Tokens
Syntactic Analysis CS45H: Programming Languages Lecture : Lexical Analysis Thomas Dillig Main Question: How to give structure to strings Analogy: Understanding an English sentence First, we separate a
More informationGenerating a Lexical Analyzer Program
lex 1 Introduction A software tool known aslex enables you solve a wide class of problems drawn from text processing, code enciphering, compiler writing, and other areas. In text processing, you might
More information10/4/18. Lexical and Syntactic Analysis. Lexical and Syntax Analysis. Tokenizing Source. Scanner. Reasons to Separate Lexical and Syntactic Analysis
Lexical and Syntactic Analysis Lexical and Syntax Analysis In Text: Chapter 4 Two steps to discover the syntactic structure of a program Lexical analysis (Scanner): to read the input characters and output
More informationI. OVERVIEW 1 II. INTRODUCTION 3 III. OPERATING PROCEDURE 5 IV. PCLEX 10 V. PCYACC 21. Table of Contents
Table of Contents I. OVERVIEW 1 II. INTRODUCTION 3 1. FEATURES 3 2. CONVENTIONS 3 3. READING THIS MANUAL 3 III. OPERATING PROCEDURE 5 1. WRITING GRAMMAR DESCRIPTION FILES FOR PCYACC 5 2. GENERATING THE
More informationDOID: A Lexical Analyzer for Understanding Mid-Level Compilation Processes
www.ijecs.in International Journal Of Engineering And Computer Science ISSN: 2319-7242 Volume 5 Issue 12 Dec. 2016, Page No. 19507-19511 DOID: A Lexical Analyzer for Understanding Mid-Level Compilation
More information10/5/17. Lexical and Syntactic Analysis. Lexical and Syntax Analysis. Tokenizing Source. Scanner. Reasons to Separate Lexical and Syntax Analysis
Lexical and Syntactic Analysis Lexical and Syntax Analysis In Text: Chapter 4 Two steps to discover the syntactic structure of a program Lexical analysis (Scanner): to read the input characters and output
More informationLex Spec Example. Int installid() {/* code to put id lexeme into string table*/}
Class 5 Lex Spec Example delim [ \t\n] ws {delim}+ letter [A-Aa-z] digit [0-9] id {letter}({letter} {digit})* number {digit}+(\.{digit}+)?(e[+-]?{digit}+)? %% {ws} {/*no action and no return*?} if {return(if);}
More information1. INTRODUCTION TO LANGUAGE PROCESSING The Language Processing System can be represented as shown figure below.
UNIT I Translator: It is a program that translates one language to another Language. Examples of translator are compiler, assembler, interpreter, linker, loader and preprocessor. Source Code Translator
More informationCS 403: Scanning and Parsing
CS 403: Scanning and Parsing Stefan D. Bruda Fall 2017 THE COMPILATION PROCESS Character stream Scanner (lexical analysis) Token stream Parser (syntax analysis) Parse tree Semantic analysis Abstract syntax
More informationRecognition of Tokens
Recognition of Tokens Lecture 3 Section 3.4 Robb T. Koether Hampden-Sydney College Mon, Jan 19, 2015 Robb T. Koether (Hampden-Sydney College) Recognition of Tokens Mon, Jan 19, 2015 1 / 21 1 A Class of
More informationAdvances in Compilers
Advances in Compilers Prof. (Dr.) K.R. Chowdhary, Director COE Email: kr.chowdhary@jietjodhpur.ac.in webpage: http://www.krchowdhary.com JIET College of Engineering August 4, 2017 kr chowdhary Compilers
More informationComputer Science Department Carlos III University of Madrid Leganés (Spain) David Griol Barres
Computer Science Department Carlos III University of Madrid Leganés (Spain) David Griol Barres dgriol@inf.uc3m.es Introduction: Definitions Lexical analysis or scanning: To read from left-to-right a source
More informationCompil M1 : Front-End
Compil M1 : Front-End TD1 : Introduction à Flex/Bison Laure Gonnord (groupe B) http://laure.gonnord.org/pro/teaching/ Laure.Gonnord@univ-lyon1.fr Master 1 - Université Lyon 1 - FST Plan 1 Lexical Analysis
More informationLexical Analysis. Lexical analysis is the first phase of compilation: The file is converted from ASCII to tokens. It must be fast!
Lexical Analysis Lexical analysis is the first phase of compilation: The file is converted from ASCII to tokens. It must be fast! Compiler Passes Analysis of input program (front-end) character stream
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 informationLexical Analysis - Flex
Lexical Analysis - Flex CMPSC 470 Lecture 03 Topics: Flex / JFlex A. Lex/Flex Lex and flex (fast lex) are programs that 1. Take, as input, a program containing regular expressions (describing patterns
More informationFSASIM: A Simulator for Finite-State Automata
FSASIM: A Simulator for Finite-State Automata P. N. Hilfinger Chapter 1: Overview 1 1 Overview The fsasim program reads in a description of a finite-state recognizer (either deterministic or non-deterministic),
More informationJFlex Regular Expressions
JFlex Regular Expressions Lecture 17 Section 3.5, JFlex Manual Robb T. Koether Hampden-Sydney College Wed, Feb 25, 2015 Robb T. Koether (Hampden-Sydney College) JFlex Regular Expressions Wed, Feb 25, 2015
More informationUlex: A Lexical Analyzer Generator for Unicon
Ulex: A Lexical Analyzer Generator for Unicon Katrina Ray, Ray Pereda, and Clinton Jeffery Unicon Technical Report UTR 02a May 21, 2003 Abstract Ulex is a software tool for building language processors.
More informationGechstudentszone.wordpress.com
Unit 7 LEX AND YACC-1 Lex is a program generator designed for lexical processing of character input streams. It accepts a high-level, problem oriented specification for character string matching, and produces
More informationDavid Griol Barres Computer Science Department Carlos III University of Madrid Leganés (Spain)
David Griol Barres dgriol@inf.uc3m.es Computer Science Department Carlos III University of Madrid Leganés (Spain) OUTLINE Introduction: Definitions The role of the Lexical Analyzer Scanner Implementation
More informationLexical Analysis. Finite Automata
#1 Lexical Analysis Finite Automata Cool Demo? (Part 1 of 2) #2 Cunning Plan Informal Sketch of Lexical Analysis LA identifies tokens from input string lexer : (char list) (token list) Issues in Lexical
More informationRay Pereda Unicon Technical Report UTR-02. February 25, Abstract
iflex: A Lexical Analyzer Generator for Icon Ray Pereda Unicon Technical Report UTR-02 February 25, 2000 Abstract iflex is software tool for building language processors. It is based on flex, a well-known
More informationLanguages and Compilers
Principles of Software Engineering and Operational Systems Languages and Compilers SDAGE: Level I 2012-13 4. Lexical Analysis (Scanning) Dr Valery Adzhiev vadzhiev@bournemouth.ac.uk Office: TA-121 For
More informationLesson 10. CDT301 Compiler Theory, Spring 2011 Teacher: Linus Källberg
Lesson 10 CDT301 Compiler Theory, Spring 2011 Teacher: Linus Källberg Outline Flex Bison Abstract syntax trees 2 FLEX 3 Flex Tool for automatic generation of scanners Open-source version of Lex Takes regular
More informationInterpreter. Scanner. Parser. Tree Walker. read. request token. send token. send AST I/O. Console
Scanning 1 read Interpreter Scanner request token Parser send token Console I/O send AST Tree Walker 2 Scanner This process is known as: Scanning, lexing (lexical analysis), and tokenizing This is the
More informationLexical Analysis. Chapter 2
Lexical Analysis Chapter 2 1 Outline Informal sketch of lexical analysis Identifies tokens in input string Issues in lexical analysis Lookahead Ambiguities Specifying lexers Regular expressions Examples
More informationA Pascal program. Input from the file is read to a buffer program buffer. program xyz(input, output) --- begin A := B + C * 2 end.
A Pascal program program xyz(input, output); var A, B, C: integer; begin A := B + C * 2 end. Input from the file is read to a buffer program buffer program xyz(input, output) --- begin A := B + C * 2 end.
More informationCompiler phases. Non-tokens
Compiler phases Compiler Construction Scanning Lexical Analysis source code scanner tokens regular expressions lexical analysis Lennart Andersson parser context free grammar Revision 2011 01 21 parse tree
More informationLexical Analysis. Textbook:Modern Compiler Design Chapter 2.1
Lexical Analysis Textbook:Modern Compiler Design Chapter 2.1 A motivating example Create a program that counts the number of lines in a given input text file Solution (Flex) int num_lines = 0; %% \n ++num_lines;.
More information