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I need to learn lex and yacc (i'm using bison and flex for them) can anybody suggest any good tutorial for them because I only found junk by searching on google. Tutorials that don't seem to be very helpfull.
I'm sorry if I'm not asking in the right place, this being a C forum. I thought that because they are so C related languages somebody here knows how to help me.
Thank you very much!
Moved to Tech.
Or a book perhaps - try a library
http://www.amazon.com/lex-yacc-Doug-...4750571&sr=8-1
I read somewhere in this form that there is an multi threaded alternative.
I think this is a serious drawback did you consider the alternatives.
maybe they are easier to master as well.
I don't know of any good tutorials, but if you have specific questions I can try to answer them.Quote:
Originally Posted by spank
why is this grammar wrong ?Code:%{
void yyerror(char*);
%}
%token NUMAR VARIABILA
%%
operand: NUMAR
| operand '+' NUMAR
;
adunare: operand '+' operand {
printf("%d\n",$1+$3);
}
;
%%
int main()
{
yyparse();
return 0;
}
void yyerror(char *s)
{
printf("Eroare: %s\n",s);
}
A multi-threaded alternative to a parser? I don't really think so. At most, you could build a producer/consumer model with the lexer and parser, but since parsing is largely I/O-bound, the gains would be rather irrelevant.
The grammar is wrong because it is ambiguous.
The expression "1 + 2" could be
NUMAR=operand '+' NUMAR
or
NUMAR=operand=adunare '+' NUMAR=operand=adunare.
why is that ambiguous? please explain in more words because I don't understand.
this is better i belive... but why does it work only for the first sequence i enter ? and for the second it gives me syntax errorCode:instructiune : expresie { printf("%d\n",$1); }
;
expresie : expresie '+' NUMAR { $$=$1+$3;}
| expresie '-' NUMAR { $$=$1-$3;}
| NUMAR { $$=$1; }
;
How can I make it more obvious? There are two ways to resolve the expression with your previous grammar, and neither is preferable to the other, so, since yacc can't decide which to use, it fails.
The new grammar is better. But I don't understand your error.
I should of done this... this is because i wanted to enter expresions one after the other. thank you... more questions coming soon :PCode:instructiune : expresie { printf("%d\n",$1); } instructiune
|;
expresie : expresie '+' NUMAR { $$=$1+$3;}
| expresie '-' NUMAR { $$=$1-$3;}
| NUMAR { $$=$1; }
;