Hi,
The more I study flex/bison, the more confused I got about when to use
what actions and what to put in lexer and what to put in grammar.
For example, for an assignment,
x=10
it can be processed by the lexer,
[[:alpha:]_][[:alnum:]_]=[[:digit:]+] { /* parse yytext to get the
name and value, then do the assignment */ }
or use these lex rules
%x ASSIGNMENT
%%
[[:alpha:]_][[:alnum:]_]= { BEGIN(ASSIGNMENT); /*save varaible name*/ }
<ASSIGNMENT>[[:digit:]]+ {
/* get the value and assign to the saved variable name*/
BEGIN(INITIAL);
}
Alternatively, the lexer can just do
[[:alpha:]_][[:alnum:]_] { /*save name somewhere for bison use */
return TOK_NAME; }
= { return '='; }
[[:digit:]+] { /*save value somwhere for bison
use*/ return TOK_VALUE; }
Then, bison grammar can be something like this.
assignment: TOK_NAME '=' TOK_VALUE { /*do the assignment */}
There just seem to be too many possible ways of implementations. Could
anybody let me know how to decide which implementation to use in
practical scenarios?
--
Regards,
Peng
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