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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 ...
A Flex lexical analyzer usually has time complexity () in the length of the input. That is, it performs a constant number of operations for each input symbol. This constant is quite low: GCC generates 12 instructions for the DFA match loop.
[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] Lex reads an input stream specifying the lexical analyzer and writes source code which implements the lexical analyzer in the C ...
Lexical analysis mainly segments the input stream of characters into tokens, simply grouping the characters into pieces and categorizing them. However, the lexing may be significantly more complex; most simply, lexers may omit tokens or insert added tokens.
A compiler is likely to perform some or all of the following operations, often called phases: preprocessing, lexical analysis, parsing, semantic analysis (syntax-directed translation), conversion of input programs to an intermediate representation, code optimization and machine specific code generation.
The () parser is a deterministic pushdown automaton with the ability to peek on the next input symbols without reading. This peek capability can be emulated by storing the lookahead buffer contents in the finite state space, since both buffer and input alphabet are finite in size.
Note that the preprocessor is in principle language agnostic, and is a lexical preprocessor, working at the lexical analysis level – it does not do parsing, and thus is unable to do any processing specific to C syntax. The input to the compiler is the translation unit, and thus it does not see any preprocessor directives, which have all been ...
In computer programming and computer science, "maximal munch" or "longest match" is the principle that when creating some construct, as much of the available input as possible should be consumed. The earliest known use of this term is by R.G.G. Cattell in his PhD thesis [ 1 ] on automatic derivation of code generators for compilers .