We'll use Integer , Char , Real , String
and Id to denote the syntactic classes of
integers, characters, real numbers, strings and identifiers, respectively.
As in C++, characters are quoted with the single quotes ', while
strings are quoted with double quotes ". An identifier is
any sequence of alphanumeric of characters that begins with a letter.
In addition, we'll use the syntactic class
Stmt to denote any valid combination of C++ and Prop
statements.