Calculator, handy recursive descent parser in C#

BNF Grammar used in the project:

exp -> exp "+" term
     | exp "-" term
     | term

term -> term "*" factor
     | term "/" factor
     | factor

factor -> "+" factor
     | "-" factor
     | "(" exp ")"
     | number

number -> [0-9]+ ([.][0-9]+)? ([eE](+|-)?[0-9]+)