Write an unambiguous BNF grammar, define attributes for the grammar symbols and attach attribute rules and predicates to the BNF productions for assignment statements with arithmetic expressions and follow it strictly. Allow binary operations +, -, *, and / and unary operations + and -. The unary operations should have equal priority which is higher than the priority of * and /; * and / should have equal priority which is higher than the priority of + and -. An expression in parentheses should be possible to use as an operand for any operation. The parentheses have the highest priority. Use as a goal symbol and id as a terminal symbol representing an identifier. Recognize single letters as identifiers. Example sentences:

a = b + a * c;

b = (x + y) * b;

b = ---b;

x = -(a * b) + c;

x = (((a * b))) - + c;