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Lex is a computer program that generates lexical analyzers ("scanners" or "lexers"). [1] [2] It is commonly used with the yacc parser generator and is the standard lexical analyzer generator on many Unix and Unix-like systems. An equivalent tool is specified as part of the POSIX standard. [3]
Flex (fast lexical analyzer generator) is a free and open-source software alternative to lex. [2] It is a computer program that generates lexical analyzers (also known as "scanners" or "lexers").
The resulting program is faster than its table-driven counterpart [1] and much easier to debug and understand. Moreover, this approach often results in smaller lexers, [ 1 ] as re2c applies a number of optimizations such as DFA minimization and the construction of tunnel automaton. [ 9 ]
The RE/flex lexical analyzer generator accepts an extended syntax of Flex lexer specifications as input. The RE/flex specification syntax is more expressive than the traditional Flex lexer specification syntax and may include indentation anchors, word boundaries, lazy quantifiers (non-greedy, lazy repeats), and new actions such as wstr() to ...
Tokens are often defined by regular expressions, which are understood by a lexical analyzer generator such as lex, or handcoded equivalent finite-state automata. The lexical analyzer (generated automatically by a tool like lex or hand-crafted) reads in a stream of characters, identifies the lexemes in the stream, and categorizes them into tokens.
Yacc (Yet Another Compiler-Compiler) is a computer program for the Unix operating system developed by Stephen C. Johnson.It is a lookahead left-to-right rightmost derivation (LALR) parser generator, generating a LALR parser (the part of a compiler that tries to make syntactic sense of the source code) based on a formal grammar, written in a notation similar to Backus–Naur form (BNF). [1]
In more detail, in a compiler, the lexer performs one of the earliest stages of converting the source code to a program. It scans the text to extract meaningful tokens, such as words, numbers, and strings. The parser analyzes sequences of tokens attempting to match them to syntax rules representing language structures, such as loops and ...
JavaCC (Java Compiler Compiler) is an open-source parser generator and lexical analyzer generator written in the Java programming language. [2] JavaCC is similar to yacc in that it generates a parser from a formal grammar written in EBNF notation. Unlike yacc, however, JavaCC generates top-down parsers.