Lexical Definitions

The following defines regular expressions for the lexical classes of tokens. The grammatical conventions are:

• All uppercase letters can either be upper or lower case. NESL is case insensitive.
• The brackets ( ) enclose an expression. The brackets [ ] enclose a character set, any one of which must match. The expression 0-9 within square brackets means all digits and the expression A-Z means all letters. The symbol as the first character within square brackets means a compliment character set (all characters excepting the following ones).
• The symbol * means the previous expression can be repeated as many times as needed, the symbol + means the previous expression can be repeated as many times as needed but at least once, and the symbol ? means the previous expression can be matched either once or not at all.