The LEX & YACC Page

Time 2020-10-27 22:05:50

Web Name: The LEX & YACC Page

WebSite: http://dinosaur.compilertools.net

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A compiler or interptreter for a programminning languageis often decomposed into two parts:Lex helps write programs whose control flow is directed byinstances of regular expressions in the input stream. It is wellsuited for editor-script type transformations and for segmentinginput in preparation for a parsing routine.Lex source is a table of regular expressions and correspondingprogram fragments. The table is translated to a programwhich reads an input stream, copying it to an output stream andpartitioning the input into strings which match the given expressions.As each such string is recognized the corresponding program fragmentis executed. The recognition of the expressions isperformed by a deterministic finite automaton generated by Lex.The program fragments written by the user are executed in theorder in which the corresponding regular expressions occur in theinput stream.Computer program input generally has some structure;in fact, every computer program that does inputcan be thought of as defining an ``input language''which it accepts. An input language may be as complexas a programming language, or as simple as a sequenceof numbers. Unfortunately, usual input facilities arelimited, difficult to use, and often are lax aboutchecking their inputs for validity.Yacc provides a general tool for describing theinput to a computer program. The Yacc user specifiesthe structures of his input, together with code to beinvoked as each such structure is recognized. Yaccturns such a specification into a subroutine that han-dles the input process; frequently, it is convenientand appropriate to have most of the flow of control inthe user's application handled by this subroutine.flex is a tool for generating scanners: programs which recognized lexicalpatterns in text. flex reads the given input files, or its standardinput if no file names are given, for a description of a scanner to generate.The description is in the form of pairs of regular expressions and Ccode, called rules. flex generates as output a C source file, `lex.yy.c',which defines a routine `yylex()'. This file is compiled andlinked with the `-lfl' library to produce an executable.When the executable is run, it analyzes its input for occurrencesof the regular expressions. Whenever it finds one,it executes the corresponding C code. Bison is a general-purpose parser generator that converts a grammar description for an LALR(1) context-free grammar into a C program toparse that grammar. Once you are proficient with Bison, you may use it to develop a wide range of language parsers, from those used in simpledesk calculators to complex programming languages. Bison is upward compatible with Yacc: all properly-written Yacc grammars ought to work with Bison with no change. Anyone familiar withYacc should be able to use Bison with little trouble. Lex & YaccJohn R. Levine, Tony Mason, Doug Brown Paperback - 366 pages 2nd/updated edition (October 1992)O'Reilly & AssociatesISBN: 1565920007Compilers:Principles, Techniques, and ToolsAlfred V. Aho, Ravi Sethi, Jeffrey D. UllmanAddison-Wesley Pub CoISBN: 0201100886ModernCompiler Implementation in CAndrew W. Appel, Maia GinsburgHardcover - 560 pages Rev expand edition (January 1998)Cambridge University PressISBN: 052158390X

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