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Flex: The Lexical Scanner Generator

by G. T. Nicol

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128 Pages, plus detachable Quick Reference Card.
Cover Price: $20.00
February 1993, for Flex Version 2.3.7
ISBN 1-882114-21-3
Plastic spine
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This manual is primarily designed as a reference but can also be used as an introduction to Flex. The manual has many examples, ranging from a simple scanner that replaces one work with another, to more complex examples such as a jargon converter. The manual contains a chapter providing useful snippets that you can include in your own scanners to handle comments, dates, numbers, and the like. There is a short chapter with a quick overview of Lex, comparing and contrasting it to Flex. There is also a long chapter on how Flex interfaces with Bison and C.

Flex is a lexical scanner generator. It converts a high-level description into a C program that can perform multiple tasks. It can read a file; group the characters within it into units such as numbers, keywords or strings; return tokens that match the types of unit and more.

One example of Flex's usefulness is as a translator. In a compiler, the syntax checker must receive a stream of tokens that represent parts of its grammar, not plain characters. A lexical scanner like Flex sits between the file and the syntax checker. It reads the file, groups the characters, and passes tokens to the syntax checker in a vocabulary it can understand.

The languages used by a programmer to create a description for the scanner is a high-level language that is much more suitable for describing scanners than the C language is. Although you can write scanners in C or similar languages, Flex is quicker and much more convenient. Flex produces fast scanners and is largely POSIX compatible.

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Updated: $Date: 2006/05/01 10:04:13 $ $Author: ramprasadb $