Flex与Bison构建编译器：Aaby的2005年教程

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"《使用Flex和Bison构建编译器》是一份由Anthony A.Aaby撰写的重要教材，于2005年发布。作者是Walla Walla College的计算机科学教授，其电子邮箱为aabyan@wwc.edu。该书是针对编译器构造课程设计的，主要采用Flex和Bison这两种流行的工具进行讲解，这两者在解析器生成器领域中扮演着关键角色。 Flex是一种广泛用于编写输入处理程序的工具，它专注于解析文本流并产生与之匹配的输入事件。而Bison则是一个强大的语法分析器生成器，用于根据上下文无关文法（Context-Free Grammar, CFG）构建解析器。本书旨在引导读者理解和实现一个编译器的核心组件，从词法分析到语法分析，通过实际案例展示了如何利用Flex和Bison来处理语言的词汇和结构规则。版本更新至2005年4月22日，版权归属安东尼·阿拜，强调了材料的开放性和免费分发原则，遵循Open Publication License v1.0或更高版本的规定。作者鼓励个人和商业使用这本书，但必须保留版权声明，并且分发方式需符合许可证条款，可在www.opencontent.org/openpub找到详细条款。书中不仅包含理论知识，还提供了LaTeX源代码供读者请求获取，以方便深入学习和实践。作者明确指出，无需特别授权即可复制和传播这本书，无论是纸质版还是电子版，只要不侵犯版权声明和保持许可协议的执行。这本资源对于学习编译器原理和技术的学生和开发者来说是一份宝贵的资料，涵盖了词法分析、语法分析、解析器设计以及用Flex和Bison实现的关键步骤，是理解现代软件开发中核心技术的理想入门指南。"

DIGIT [0-9]

ID [a-z][a-z0-9]*

Token deﬁnitions and actions

C subroutines

The second section of the Lex ﬁle gives the regular expressions for each token

to be recognized and a corresponding action. Strings of one or more digits are

recognized as an integer and thus the value INT is returned to the parser. The

reserved words of the language are strings of lower case letters (upper-case may

be used but must be treated diﬀerently). Blanks, tabs and newlines are ignored.

All other single character symbols are returned as themselves (the s canner places

all input in the string yytext).

C and scanner declarations

”:=” { return(ASSGNOP); }

{DIGIT}+ { return(NUMBER); }

do { return(DO); }

else { return(ELSE); }

end { return(END); }

ﬁ { return(FI); }

if { return(IF); }

in { return(IN); }

integer { return(INTEGER); }

let { return(LET); }

read { return(READ); }

skip { return(SKIP); }

then { return(THEN); }

while { return(WHILE); }

write { return(WRITE); }

{ID} { return(IDENTIFIER); }

[ \t\n]+ /* blank, tab, new line: eat up whitespace */

. { return(yytext[0]); }

C subroutines

The values associated with the tokens are the integer values that the scanner

returns to the parser upon recognizing the token.

Figure 3.1 gives the format of some of the regular expressions that may be

used to deﬁne the tokens. There is a global variable yylval is accessible by

both the scanner and the parser and is used to store additional information

about the token.

The third section of the ﬁle is empty in this example but may contain C

code associated with the actions.

Compiling the Lex ﬁle with the command lex ﬁle.lex (ﬂex ﬁle.lex) results in

the production of the ﬁle lex.yy.c which deﬁnes the C function yylex(). One each

invocation, the function yylex() scans the input ﬁle an returns the next token.

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