Compiler Principle(1)Lex and Yacc

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magic_dreamer

最新推荐文章于 2025-08-11 22:14:14 发布

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本文介绍了Lex与Yacc的基本概念及其使用方法。Lex用于构建词法分析器，而Yacc则用于创建语法分析器。文章通过具体示例展示了如何用Lex统计单词数量，并用Yacc实现简单的语法解析。

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Compiler Principle(1)Lex and Yacc

1. Some Concept
Abstract Syntax Tree AST
Lex - Lexical Analyzer
Yacc - Yet Another Compiler Compiler

2. Lex
>lex --version
flex 2.5.35 Apple(flex-31)

Declare the wordCount
%{

int wordCount = 0;

chars [A-za-z\_\'\.\"]

numbers ([0-9])+

delim [" "\n\t]

whitespace {delim}+

words {chars}+

%%

Lex Rules
{words} {

wordCount++;

/* increase the word count by one*/ }

{whitespace}

{ /* do nothing*/ }

{numbers}

{ /* one may want to add some processing here*/ }

%%

The last part is usually, the main Function
void main()

{

yylex();

/* start the analysis*/

printf(" No. of words:%d\n", wordCount);

}

int yywrap(){

return 1;

}

3. Yacc
>yacc -V
bison (GNU Bison) 2.3 Written by Robert Corbett and Richard Stallman.

>yacc filename.y

Declaration
%{
#typedef char* string; /* to specify token types as char* */
#define YYSTYPE string /*a Yacc variable which has the value of returned token */
%}
%token NAME EQ AGE
%%

Grammar Rules
file: record file
| record ;
record: NAME EQ AGE {
printf(“%s is now %s years old!, $1, $3);
};
%%

C Function
void main(){
yyparse();
}
int yyerror(char* msg){
printf(“Error: %s encountered \n”, msg);
}

>yacc -d filename.y

4. Lex and Yacc
Take the example in
http://www.ualberta.ca/dept/chemeng/AIX-43/share/man/info/C/a_doc_lib/aixprggd/genprogc/ie_prog_4lex_yacc.htm

I need more time to understand more.

References:
java AST
http://rwl6813021.iteye.com/blog/174666
http://lym6520.iteye.com/blog/747840

go AST
http://golang.org/src/pkg/go/ast/example_test.go
https://github.com/Joinhack/peony/blob/master/mole/gowalker.go
https://github.com/Joinhack/peony/blob/master/mole/comment_expr.y
https://github.com/Joinhack/peony/blob/master/mole/gowalker.go

Yacc
http://www.ibm.com/developerworks/cn/linux/sdk/lex/
http://blog.youkuaiyun.com/yuucyf/article/details/7108590
http://www.360doc.com/content/12/0806/19/532901_228697197.shtml

Yacc and Lex
http://epaperpress.com/lexandyacc/
http://www.ualberta.ca/dept/chemeng/AIX-43/share/man/info/C/a_doc_lib/aixprggd/genprogc/ie_prog_4lex_yacc.htm