expression -> term r-expression r-expression -> epsilon | add-term r-expression | subtract-term r-expression * add-term -> "+" term * subtract-term -> "-" term term -> factor r-term r-term -> epsilon | multiply-factor r_term | divide-factor r_term * multiply-factor -> "*" factor * divide-factor -> "/" factor factor -> "(" expression ")" * | integer
Example 9: Grammar for a four-function calculator.