Extended Backus-Naur Form (EBNF)

• Use square brackets [] for optional parts.
  BNF:

     <ret-stmnt> -> return  <int-exprn> ;
                     |  return ;
  

  EBNF:

     <ret-stmnt> -> return [ <int-exprn> ] ;
  

• Use braces {} to repeat indefinitely:
  BNF:

     <declist> -> <declaration> , <declist> 
                  | <declaration>
  

  EBNF:

     <declist> -> <declaration> {, <declaration> }
  

  or alternatively, use ellipsis:

     <declist> -> <declaration> [, <declaration> ] ...
  

• Use braces {}⁺ to repeat at least once:
  BNF:

     <block> -> begin  <stmnt-list>  end
     <stmnt-list> -> <stmnt> <stmnt-list>
                     | <stmnt>
  

  EBNF:

     <block> -> begin { <stmnt> }+ end
  

• Use | inside a rule for alternatives:
  BNF:

     <expr> -> <term> * <expr> 
               |  <term> / <expr> 
  

  EBNF:

     <expr> -> <term> (* | /) <expr>