Pdf an exploration on lexical analysis researchgate. Lexical analysis or scanning is the process where the stream of. This article will describe how to build the first phase of a compiler, the lexer. Lexical analysis is the very first phase in the compiler designing. What constitutes the stages of the compilation process. Goals of lexical analysis convert from physical description of a program into sequence of of tokens. Lexical analysis article about lexical analysis by the free. The more information a compiler has, the more defects it can find.
The stream of characters making up the source program or other input is read one at a time and grouped into. Each token represents one logical piece of the source file a keyword, the name of a variable, etc. Lexical analysis is the process of converting a sequence of characters such as in a computer program or web page into a sequence of tokens strings with an identified. Bruda winter 2016 t he l exical a nalyzer main role.
The stream of tokens is sent to the parser for syntax analysis. The reason why lexical analysis is a separate phase simplifies the design of the compiler ll1 or lr1 parsing with 1 token lookahead would not be possible multiple characterstokens to match provides efficient implementation systematic techniques to implement lexical analyzers by hand or automatically from specifications. Syntax analyzers are based directly on the grammars discussed in chapter 3. It presents a major common rational characteristic, being more or less intuitive, personal, and subjective. Cs143 handout 04 summer 2012 june 27, 2012 lexical analysis handout written by maggie johnson and julie zelenski. It takes the modified source code from language preprocessors that are written in the form of sentences. A lexical analyser is used in various applications like text editors, information retrieval system, pattern recognition programs and language compilers. Compilers questions and answers lexical analysis 2. These questions are frequently asked in all trb exams, bank clerical exams, bank po, ibps exams and all entrance exams 2017 like cat exams 2017, mat exams 2017, xat exams 2017, tancet exams 2017, mba.
These questions are frequently asked in all trb exams, bank clerical exams, bank po, ibps exams and all entrance exams 2017 like cat exams 2017, mat exams 2017, xat exams 2017, tancet exams 2017, mba exams 2017, mca exams 2017 and ssc 2017 exams. Making model is the basis of the lexical analyzer constructing. Lexical analyser phases compiler design lec5 bhanu. Read the input characters and produce a sequence of tokens that will be processed by the parser. A program or function that performs lexical analysis is called a lexical. Essentially, lexical analysis means grouping a stream of letters or sounds into sets of units that represent meaningful syntax. Since the cost of scanning grows linearly with the number of characters, and the constant costs are low, pushing lexical analysis from the parser into a separate. What is an example of a lexical error in compilers. Lexical analysis syntax analysis scanner parser syntax. Compiler design lexical analysis in compiler design tutorial.
Compiler design lexical analysis in compiler design. Compiler efficiency is improved specialized buffering techniques for reading characters speed up the compiler process. Its job is to turn a raw byte or character input stream coming from the source. It occurs when compiler does not recognise valid token string while scanning the. Simplicity of design of compiler the removal of white spaces and comments enables the syntax analyzer for efficient syntactic constructs. Lexical analysis or scanning is the process where the stream of characters making up the source program is read from lefttoright and grouped into tokens. Apr 12, 2020 lexical analysis is the very first phase in the compiler designing. Chapter 1 lexical analysis using jflex page 1 of 39 chapter 1 lexical analysis using jflex tokens the first phase of compilation is lexical analysis the decomposition of the input into tokens. The input is a high level language program, such as a c program in. Javacc takes just one input file called the grammar file, which is then used to create both classes for lexical analysis, as well as for the parser. A source file is an ordered sequence of unicode characters. The syntax and semantic analysis phases usually handle a large fraction of the errors detectable by the compiler.
These syntaxes are broke into series of tokens by the lexical analyzer and the whitespace or the comments are removed in the source code. In the previous unit, we observed that the syntax analyzer that were going to develop will consist of two main modules, a tokenizer and a parser, and the subject of this unit is the tokenizer. Lecture 7 september 17, 20 1 introduction lexical analysis is the. In computer science, lexical analysis, lexing or tokenization is the process of converting a sequence of characters such as in a computer program or web page into a sequence of tokens strings with an assigned and thus identified meaning. If the lexical analyzer finds a token invalid, it generates an. Lexical analysis can be implemented with the deterministic finite automata. The word lexical in lexical analysis, its meaning is extracted from the word lexeme. Cooper, linda torczon, in engineering a compiler second edition, 2012. Error detection and recovery in compiler geeksforgeeks. Lexical analysis is a concept that is applied to computer science in a very similar way that it is applied to linguistics.
Errors where the token stream violates the structure rules syntax. Lexical analyser being the first phase of the compilation process it deals with the. Chapter 4 lexical and syntax analysis recursivedescent. The lexical analysis breaks this syntax into a series of tokens. It takes the modified source code which is written in the form of sentences. Programming languages lexical and syntax analysis cmsc 4023 chapter 4 1 4. A parser takes tokens and builds a data structure like an abstract syntax tree ast. These errors are detected during the lexical analysis phase. Its job is to turn a raw byte or char acter input stream coming from the source.
Lexical analysis is the first phase of compiler also known as scanner. Unlike the other tools presented in this chapter, javacc is a parser and a scanner lexer generator in one. Lexical analysis handout written by maggie johnson and julie zelenski. At the end of the article, you will get your hands dirty with a challenge. Tools for constructing scanners severaltoolsforbuildinglexicalanalyzersfromspecialpurposenotationbased onregularexpressions. The terminal symbols of the lexical grammar are the characters of the unicode character set, and the lexical grammar specifies how characters are combined to form tokens tokens, white space white space, comments comments, and pre. Usually implemented as subroutine or coroutine of parser. As the first phase of a compiler, the main task of the lexical analyzer is to read the input characters of the source program, group them into lexemes, and produce as output a sequence of tokens for each lexeme in the source program. Compiler design mcq with answers pdf compiler mcq questions. Lexical analysis article about lexical analysis by the.
A lexical analyzer can be used to do lexical analyzing in many kinds of software such as language compiler and document editor. What are some examples of errors a lexical analyzer could detect. In linguistics, it is called parsing, and in computer science, it can be called parsing or. But we limit our discussion in this paper to language compilers. A graphical display shows the complete details of each individual stage of the compilation process comprehensively. The lexer, also called lexical analyzer or tokenizer, is a program that breaks down the input source code into a sequence of lexemes. Tokens are sequences of characters with a collective meaning. In other words, it helps you to converts a sequence of characters into a sequence of tokens. The modified source code is taken from the language preprocessors which are written as sentences.
A compiler is a combined lexer and parser, built for. Lexical analysis or scanning is the process where the stream of characters making up the source program is read from left toright and grouped into tokens. Originally, the separation of lexical analysis, or scanning, from syntax analysis, or parsing, was justified with an efficiency argument. Welcome to unit 2 in which were going to talk about lexical analysis. Compiler design lecture 4 elimination of left recursion and left factoring the grammars duration. A lexer takes the modified source code which is written in the form of sentences. The first phase of the compiler is the lexical analysis. It presents a major common rational characteristic, being more or. A lexical token is a sequence of characters that can be treated as a unit in the grammar of the programming languages. Some compilers operate in a forgiving mode but have a strict or pedantic mode, if you request it. It contains well written, well thought and well explained computer science and programming articles, quizzes and practicecompetitive programmingcompany interview questions. Lexical and syntax analysis why should we discuss the implementation of parts of a compiler. The basics lexical analysis or scanning is the process where the stream of characters making up the source program is read from lefttoright and grouped into tokens. Compilerlexical analyzer you are encouraged to solve this task according to the task description, using any language you may know.
Jan 09, 2019 compiler design lexical analyzer in detail. Lexeme is an abstract unit of morphological analysis in linguistics. The scanninglexical analysis phase of a compiler performs the task of reading the source program as a file of characters and dividing up into tokens. A parser with comments or white spaces is more complex 2 compiler efficiency is improved. The front end of a compiler performs lexical, syntactic, and semantic analysis. Lexical and syntax analyzers are needed in numerous situations outside compiler design. A lexer performs lexical analysis, turning text into tokens. The lexical analyzer breaks these syntaxes into a series of tokens, by removing any whitespace or comments in the source code. What are some examples of errors a lexical analyzer could.
In theory, token discovery lexical analysis could be done as part of the structure discovery syntactical analysis, parsing. Lexical and syntax analysis 6 issues in lexical and syntax analysis reasons for separating both analysis. Jeena thomas, asst professor, cse, sjcet palai 1 2. Lexical error are the errors which occurs during lexical analysis phase of compiler. A qualitative practical application document analysis, which includes content analysis and lexical analysis, follow classic methods like the judicial and sociological research.