[Grammatica-users] token priority?

[John Ledbetter]

Hello,

I am working with a grammar for a simple mathematical language, and I am 
having trouble implementing a unary minus sign.

In flex/bison, I would do something like...

%left PLUS MINUS
%nonassoc UNARY

// ....
somerule : expr MINUS expr
             | MINUS expr %prec UNARY


What is the equivalent construct in grammatica?

Thanks,
John.