Grammar for expressions of Assignment 1

Tokens: In the rules below tokens are either named (UPPER case) or in " "

    OPERATOR = any one of + - * / 

    NUMBER = a token that satifies the number? predicate, that is
        any proper racket number

    IDENTIFIER = any token that begins with A-Z or a-z

    DELIMITERS = the ( and ) parentheses

Rules:

    <expression> ::= NUMBER | 
                    IDENTIFIER |
                    "(" <expression> ")" |
                    "(" <expression> OPERATOR <expression> ")"