The trick simulate the nfa each state of dfa a nonempty subset of states of the nfa s e sttartat the set of nfa states reachable through. The lexical analyzer can be a convenient place to carry out some other chores like stripping out comments and white space between tokens and perhaps even some features like macros and conditional compilation although often these are handled by some sort of preprocessor which filters the input before the compiler runs. An analysis of compiler design in context of lexical analyzer. That means, when parser required string of tokens it invokes lexical analyzer. Recognitions of tokens the lexical analyzer generator lexical unit ii syntax analysis. The lexical analyzer breaks this syntax into a series of tokens. The role of the lexical analyzer in the compiler upon receiving a getnexttohen command from the parser, the lexical analyzer reads input characters until it can identify the next token. Lex is an acronym that stands for lexical analyzer generator. It converts the high level input program into a sequence of tokens. Applications of finite automata in lexical analysis and as. Lexical analyzer, syntax analyzer and semantic analyzer are the parts of this phase. Chapter 3 lexical analysis from mca 200125 at galgotias university.
Lexical analysis can be implemented with the deterministic finite automata. In order to reduce the complexity of designing and building computers, nearly all of these are made to execute relatively simple commands. Compiler design lexical analysis in compiler design compiler design lexical analysis in compiler design courses with reference manuals and examples pdf. Lexical analysis is the very first phase in the compiler designing. Compiler is responsible for converting high level language in machine language. Finite automata, lexical analysis, vending machine. There are several phases involved in this and lexical analysis is the first phase. It reads the input character and produces output sequence of tokens that the parser uses for syntax analysis.
Tokens, patterns, and lexemes a token is a set of strings over the source alphabet. Let l r be a regular language recognized by some finite automata fa. Unit ii lexical analysis 9 need and role of lexical analyzerlexical errorsexpressing tokens by regular expressionsconverting regular expression to dfa minimization of dfalanguage for specifying lexicalanalyzerslexdesign of lexical analyzer for a sample language. The role of the lexical analyzer the lexical analyzer or scanner is the first phase of a compiler. Lexical analysis in compiler design with example guru99.
Lexical analysis is a concept that is applied to computer science in a very similar way that it is applied to linguistics. A lexer takes the modified source code which is written in the form of sentences. Second is about the designing of vending machine to issue the tickets for the simple applications. The lexical analyzer is the first phase of compiler. The role of the semantic analyzer i for instance, a completely separated compiler could have a wellde ned lexical analysis and parsing stage generating a parse tree, which is passed wholesale to a semantic analyzer, which could then create a syntax tree and populate a symbol table, and then pass it all on to a code generator. It may also perform secondary task at user interface. For the love of physics walter lewin may 16, 2011 duration. Compiler efficiency is improved specialized buffering techniques for reading characters speed up the compiler process. Its main task is to read the input characters and produce a sequence of tokens for the syntax analyzer. Introduction to syntax analysis in compiler design. Ullman lecture12 the role of parser, syntactic errors and recovery actions ref.
Essentially, lexical analysis means grouping a stream of letters or sounds into sets of units that represent meaningful syntax. These syntaxes are broke into series of tokens by the lexical analyzer and the whitespace or the comments are removed in the source code. Introduction to syntax analysis in compiler design when an input string source code or a program in some language is given to a compiler, the compiler processes it in several phases, starting from lexical analysis scans the input and divides it. It takes the modified source code from language preprocessors that are written in the form of sentences. A lexical analyzer generally does nothing with combinations of tokens, a task left for a. Lexical analyzers also have a role in removing whitespace newline. Introduction to lexical analysis uppsala university. A parser is more complicated than a lexical analyzer and. Unit i introduction to compilers 9 cs8602 syllabus compiler design. Simplicity of design of compiler the removal of white spaces and comments enables the syntax analyzer for efficient syntactic constructs. Lexical analysisthe role of lexical analyzer t1109114 1 3 3. Lex is a program designed to generate scanners, also known as tokenizers, which recognize lexical patterns in text.
In this process of compilation the parser and lexical analyzer work together. Its job is to turn a raw byte or character input stream coming from the source. Its job is to turn a raw byte or char acter input stream coming from the source. Simplicity techniques for lexical analysis are less complex that those required for syntax analysis, so the lexicalanalysis process can be simpler if it separate. The lexical analysis used to identify the token with its type. Lexical analyzer reads the characters from source code and convert it into tokens. In linguistics, it is called parsing, and in computer science, it can be called parsing or.
Includes a fast standalone regex engine and library. Interaction is actually implemented by parser when it calls getnexttoken, so that the lexical analyzer processes its input stream and identify next lexeme to generate the next token for parser. The development of lexical analysis and parsing tools has been an important area of research in. A lexical token is a sequence of characters that can be treated as a unit in the grammar of the programming languages. The role of a parser, context free grammars writing a grammar, top down passing bottom up. Role of lexical analyzer lexical analyzer performs the following tasks. In turn, the lexical analyzer supplies tokens to syntax analyzer parser. Structure of a compiler lexical analysis role of lexical analyzer input buffering specification of tokens recognition of tokens lex finite automata regular expressions to automata minimizing dfa. If the lexical analyzer finds a token invalid, it generates an. Function line lexer takes as input a string of characters and returns the correspond ing stream of. The structure of a compiler 8 scanner lexical analyzer parser syntax analyzer semantic process semantic analyzer code generator intermediate code generator code optimizer parse tree abstract syntax tree w attributes nonoptimized intermediate code optimized intermediate code code genrator target machine code compiler design 40106. Its main task is to read the input characters and produce as output a sequence of tokens that the parser uses for syntax analysis. A language for specifying lexical analyzer, design of lexical analyzer generator ref. Creating a lexical analyzer with lex and flex lex or flex compiler lex source program lex.
Upon receiving a getnext tohen command from the parser, the lexical. Generates reusable source code that is easy to understand. Chapter 3 lexical analysis outline role of lexical analyzer specification of tokens recognition of. The role of lexical analysis buffing, specification of tokens. Compiler design lexical analysis in compiler design. Lexical analyzer is also responsible for eliminating comments and white spaces from the source program. More compact representation of input and easier to deal with later. The role of the lexical analyzer posted by unknown on 11. The role of lexical analyzer simple approach to design of a lexical analyzer regular expressions finite automata from regular expression to finite automata minimizing the number of states of a dfa a language for specifying lexical analyzer implementing a lexical. The term optimization in compiler design refers to the attempts that a compiler makes to produce code that is. Introduction to compilerthe structure of compiler t1412 2 2 2. Reads the source program, scans the input characters, group them into lexemes and produce the token as output. 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.
Cse304 compiler design notes kalasalingam university. It can either work as a separate module or as a submodule. Pdf the word lexical in lexical analysis, its meaning is extracted from the word lexeme. Lexical analysis is the first phase of compiler also known as scanner. The code for lex was originally developed by eric schmidt and mike lesk.
For example, a typical lexical analyzer recognizes parenthesis as tokens, but does nothing to ensure that each is matched with a. In a compiler, linear analysis is called lexical analysis or scanning. In other words, it helps you to convert a sequence of characters into a sequence of tokens. Pdf an exploration on lexical analysis researchgate. Lexical analysis syntax analysis scanner parser syntax. Also, removing the low level details of lexical analysis from the syntax analyze makes. The lexical analyzer breaks these syntaxes into a series of tokens, by removing any whitesp. Issues in lexical analysis simpler design compiler efficiency is improved compiler portability is enhanced 23.