Extended BNF

Syntactic Rules

• Use the standard ::= separator
• E.g., <source> ::= <general_term>

Semantic Rules

• Used when only a subset of the syntax makes semantic sense
• Use a :== separator
• E.g., <source> :== <dag_source> | <internal_source> | , etc.
• Extended to rules reachable from only such rules

Token Rules

• Used for rules that produce tokens
• Use a ::- separator
• E.g., <lower_word> ::- <lower_alpha><alpha_numeric>*

Character Macros

• Define character classes with regular expressions
• Use a ::: separator
• E.g., <lower_alpha> ::: [a-z]