On Sun, Jun 8, 2014 at 10:52 AM, Alexander Barrentine < alexander.barrent...@gmail.com> wrote:
> I can’t tell just now if this is the right place to be sending bug reports > for Lemon. I have identified a failing in the handling of nonassoc > precedence with the generated grammars. > Thanks. Fixed here: http://www.sqlite.org/src/info/1925f3a0a2caa709569df015a8e0d26412f1a9ff > > I detailed my findings in this StackOverflow page: > http://stackoverflow.com/questions/24051458/is-lemon-correctly-handling-nonassoc-precedence/24093576#24093576 > > Basically it comes down like this. I took a tiny grammar for example: > %nonassoc EQ. > %left PLUS. > > stmt ::= expr. > > expr ::= expr EQ expr. > expr ::= expr PLUS expr. > expr ::= IDENTIFIER. > And this generated a conflict when handling the second EQ in a series (so > something like x=y=z). The rules for nonassoc state this should be an > error, but the grammar does not detect it as such. Instead, a shift/reduce > conflict gets entered into the grammar. > State 4: > expr ::= expr * EQ expr > (1) expr ::= expr EQ expr * > expr ::= expr * PLUS expr > > EQ shift 2 > EQ reduce 1 ** Parsing conflict ** > PLUS shift 1 > {default} reduce 1 > I have locally modified the source the get around the issue, adding a > branch to the shift/reduce logic like so: > if( apx->type==SHIFT && apy->type==REDUCE ){ > spx = apx->sp; > spy = apy->x.rp->precsym; > if( spy==0 || spx->prec<0 || spy->prec<0 ){ > /* Not enough precedence information. */ > apy->type = SRCONFLICT; > errcnt++; > }else if( spx->prec>spy->prec ){ /* higher precedence > wins */ > apy->type = RD_RESOLVED; > }else if( spx->prec<spy->prec ){ > apx->type = SH_RESOLVED; > }else if( spx->prec==spy->prec && spx->assoc==RIGHT ){ /* > Use operator */ > apy->type = RD_RESOLVED; > /* associativity */ > }else if( spx->prec==spy->prec && spx->assoc==LEFT ){ /* > to break tie */ > apx->type = SH_RESOLVED; > }else if( spx->prec==spy->prec && spx->assoc==NONE) { /* > MY CHANGE HERE */ > apx->type = ERROR; > }else{ > assert( spx->prec==spy->prec && spx->assoc==NONE ); > apy->type = SRCONFLICT; > errcnt++; > } > > I’m hoping this proves useful to you. I am enjoying the tool. It is fast, > straightforward, and easy to use. > > Thank you, > Alexander Barrentine > > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
