On Wed 05 Jun 2013 12:06:30 AM CEST, Adam Smalin wrote:
During my test to get << a difference precedence then < I suspect it is impossible because after expr < expr [<] it has no idea if it will be a << expr or an < expression thus I can't tell it to have a different precedence between < and < <.Because I can't I wrote this test grammar. When I execute `a<b< <cd<e` I get << < < as I wanted. The issue is 2 shift reduce conflicts. I can't understand it. It does exactly what I want (<< before <). Its has %glr-parser at the top. Why isn't it ok shifting and reducing when it can't complete the longer rule (mainElement3). I'm just confused all over I don't see the conflict. How would I rewrite this to not have the conflict? %nonassoc DOLLAR //%left '<' %left '*' PREC %left '.' %% program: mEOS main main: | mainLoop mEOS mainLoop: mainElement | mainLoop mainElement mainElement: mainElement3 | mainElement '<' mainElement3 { printf("<\n"); } mainElement3: mainElement4 | mainElement3 '<' '<' mainElement4 { printf("<<\n"); } mainElement4: '$' VarName %prec DOLLAR { printf("varname\n"); } | mainElement2 //| mainElement '*' mainElement { printf("*\n"); } mainElement2: VAR { printf("var %s\n", yytext); } | Token { printf("token\n"); } Token: '.' VarName: VAR | VarName '.' VAR EOS: '\n' | ';' mEOS: | mEOS EOS %% state 12 6 mainElement: mainElement3 . [$end, VAR, '.', '<', '$', '\n', ';'] 9 mainElement3: mainElement3 . '<' '<' mainElement4 '<' shift, and go to state 22 '<' [reduce using rule 6 (mainElement)] $default reduce using rule 6 (mainElement) state 24 7 mainElement: mainElement '<' mainElement3 . [$end, VAR, '.', '<', '$', '\n', ';'] 9 mainElement3: mainElement3 . '<' '<' mainElement4 '<' shift, and go to state 22 '<' [reduce using rule 7 (mainElement)] $default reduce using rule 7 (mainElement) _______________________________________________ help-bison@gnu.org https://lists.gnu.org/mailman/listinfo/help-bison
If this is a possibility, you could detect a double << at the lexer level, and give the parser a special token corresponding to <<. That would simplify your grammar.
_______________________________________________ help-bison@gnu.org https://lists.gnu.org/mailman/listinfo/help-bison
