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A rule-based program, performing lexical tokenization, is called tokenizer, [1] or scanner, although scanner is also a term for the first stage of a lexer. A lexer forms the first phase of a compiler frontend in processing. Analysis generally occurs in one pass.
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 first edition (1986) is informally called the "red dragon book" to distinguish it from the second edition [5] and from Aho & Ullman's 1977 Principles of Compiler Design sometimes known as the "green dragon book". [5] Topics covered in the first edition include: Compiler structure; Lexical analysis (including regular expressions and finite ...
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, an automatic lexical analyser, is often used with Bison, to tokenise input data and provide Bison with tokens. [5] Bison was originally written by Robert Corbett in 1985. [1] Later, in 1989, Robert Corbett released another parser generator named Berkeley Yacc. Bison was made Yacc-compatible by Richard Stallman. [6]
The compiler generated by Yacc requires a lexical analyzer. Lexical analyzer generators, such as lex or flex are widely available. The IEEE POSIX P1003.2 standard defines the functionality and requirements for both Lex and Yacc.
Programming languages researchers have also responded by replacing or supplementing the principle of maximal munch with other lexical disambiguation tactics. One approach is to utilize "follow restrictions", which instead of directly taking the longest match will put some restrictions on what characters can follow a valid match.
Compiler analysis is the prerequisite for any compiler optimization, and they tightly work together. For example, dependence analysis is crucial for loop transformation. The scope of compiler analysis and optimizations vary greatly; their scope may range from operating within a basic block, to whole procedures, or even the whole program. There ...