unary negation in parsing java

Question

What I am trying to do is allowing expression like 8 - - - 2 + 3.

program ::= expr:e
            {: RESULT = ...; :}
         ;

expr ::= INTCONST:c
         {: RESULT = ...; :}
      |  binaryExpr:e
         {: RESULT = e;   :}
      |  LPAREN expr:e RPAREN
         {: RESULT = e;   :}
      |  MINUS expr:e               
         {: RESULT = - e; :}
         %prec UMINUS
      ;

binaryExpr ::= expr:e1 PLUS expr:e2
               {: RESULT = ... :}
               expr:e1 MINUS expr:e2
               {: RESULT = ... :}

For the unary negation, I tried this

      |  MINUS expr:e               
         {: RESULT = - e; :}
         %prec UMINUS

, but it says that the negative sign is a bad operand type.

Is there any tips to do unary negation?