Further, the typical actions include generating the parse tree. After recognizing the rule, it executes the C code associated with each rule. The output is a shift-reduce parser in C. Moreover, the input to Yacc is a grammar of C code that is attached to its rules. Additionally, GNU based Linux distribution include Bison, forward-compatible Yacc replacement. It is a standard utility on BSD and AT&T UNIX. Johnson developed it, and it is used in UNIX systems. Yacc stands for Yet Another Compiler-Compiler. The most popular open-source version of Lex is called flex, which stands for Fast Lexical Analyzer. When the lexer identifies that the text in the input matches a given pattern, it will execute the associated C code.Ĭ code: This section consists of C statements and functions.įurthermore, the open-source version of Lex is now distributed as a part of OpenSolaris and Plan 9 from Bell Labs. Rules: It contains regular expression patterns with C statements. Then, it outputs the source code implementing the lexer in the C language.Ī Lex file consists of the following three sections:ĭefinition: Defines macros and imports header files written in C.

Furthermore, Lex reads an input stream specifying the lexical analyzer. Generally, Lex is used with Yacc parse generator. Lex is specified as a part of the POSIX standard. It is a standard lexical analyzer generator on various UNIX systems. Mike Lex and Eric Schmidt are the original developers of Lex. Lex is a computer program that generates lexical analyzers. Lex, Lexical Analyzer, Parse Tree, Syntax Analysis, Yacc For example, Lex takes the string input to create tokens, and Yacc uses those tokenized input. Lex is a lexical analyzer whereas Yacc is a parser. Overall, the lexical analyzer performs the lexical analysis while syntax analyzer performs syntax analysis. It takes the tokens of the lexical analysis and produces a parse tree as the output. Next, the output of that phase goes to the syntax analysis.

It involves reading the source program one character at a time and converting it into meaningful lexemes (tokens). First, there is a lexical analysis phase. It goes through several phases to perform this conversion. Generally, a compiler is a software program that converts the source code into machine code. The main difference between Lex and Yacc is that Lex is a lexical analyzer which converts the source program into meaningful tokens while Yacc is a parser that generates a parse tree from the tokens generated by Lex.

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