Web References on Lex & Yacc?

Anybody has good technical references about lex & yacc on the Web? Most
resources I found are too introductive and not so technical.


BTW, here is a question I have:


Suppose during paring, you scanned a "id" of value "myvar", and you want
to return the type "ID" AND the value of it, i.e., the pair (ID,
"myvar"). Later on, suppose for the rule "statement: id EQUALS value",
you want the action to print out "$1 $3", then "$1" will generate a
syntax error. See below for the codes.


Thanks.


--Weedlet


-------------------------------------------------


lex:


ID [a-zA-Z]+
INTEGER [0-9]+
...


%%
INTEGER {yylval = atoi(yytext); return(INTEGER);}
ID {return(ID);} //adding "yylval = yytext" gives the same error ...
%%




yacc:


%token ID


statement:
                    ID EQUALS INTEGER
                    {printf("%s %d", $1, $3);}
                    ...
[You need to use %union and %type so the parser knows that ID has a
string value and INTEGER has an int value, sort of like this:


%union {
int ival;
char *sval;
}


%token <ival> INTEGER
%token <sval> ID


In the lexer, you include y.tab.h to get the definition of yylval, and
write code that sets the right union members, e.g.:


INTEGER {yylval.ival = atoi(yytext); return(INTEGER);}
ID { yylval.sval = strdup(yytext); return(ID);}


For more details, you can always take my book out of the library. -John]

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