Editing Extended Backus–Naur form (section)

==Examples==

===Syntax diagram===
[[File:Ebnf-syntax-diagram.png|thumb|alt=One possible EBNF syntax diagram |One possible EBNF [[syntax diagram]]]]

===EBNF===
Even EBNF can be described using EBNF. Consider below grammar (using conventions such as "-" to indicate set disjunction, "+" to indicate one or more matches, and "?" for optionality):

<syntaxhighlight lang="ebnf">
letter = "A" | "B" | "C" | "D" | "E" | "F" | "G"
       | "H" | "I" | "J" | "K" | "L" | "M" | "N"
       | "O" | "P" | "Q" | "R" | "S" | "T" | "U"
       | "V" | "W" | "X" | "Y" | "Z" | "a" | "b"
       | "c" | "d" | "e" | "f" | "g" | "h" | "i"
       | "j" | "k" | "l" | "m" | "n" | "o" | "p"
       | "q" | "r" | "s" | "t" | "u" | "v" | "w"
       | "x" | "y" | "z" ;

digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;

symbol = "[" | "]" | "{" | "}" | "(" | ")" | "<" | ">"
       | "'" | '"' | "=" | "|" | "." | "," | ";" | "-" 
       | "+" | "*" | "?" | "\n" | "\t" | "\r" | "\f" | "\b" ;

character = letter | digit | symbol | "_" | " " ;
identifier = letter , { letter | digit | "_" } ;

S = { " " | "\n" | "\t" | "\r" | "\f" | "\b" } ;

terminal = "'" , character - "'" , { character - "'" } , "'"
         | '"' , character - '"' , { character - '"' } , '"' ;

terminator = ";" | "." ;

term = "(" , S , rhs , S , ")"
     | "[" , S , rhs , S , "]"
     | "{" , S , rhs , S , "}"
     | terminal
     | identifier ;

factor = term , S , "?"
       | term , S , "*"
       | term , S , "+"
       | term , S , "-" , S , term
       | term , S ;

concatenation = ( S , factor , S , "," ? ) + ;
alternation = ( S , concatenation , S , "|" ? ) + ;

rhs = alternation ;
lhs = identifier ;

rule = lhs , S , "=" , S , rhs , S , terminator ;

grammar = ( S , rule , S ) * ;

</syntaxhighlight>

===Pascal===
A [[Pascal (programming language)|Pascal]]-like programming language that allows only assignments can be defined in EBNF as follows:

<syntaxhighlight lang="ebnf">
 (* a simple program syntax in EBNF - Wikipedia *)
 program = 'PROGRAM', white space, identifier, white space, 
            'BEGIN', white space, 
            { assignment, ";", white space },
            'END.' ;
 identifier = alphabetic character, { alphabetic character | digit } ;
 number = [ "-" ], digit, { digit } ;
 string = '"' , { all characters - '"' }, '"' ;
 assignment = identifier , ":=" , ( number | identifier | string ) ;
 alphabetic character = "A" | "B" | "C" | "D" | "E" | "F" | "G"
                      | "H" | "I" | "J" | "K" | "L" | "M" | "N"
                      | "O" | "P" | "Q" | "R" | "S" | "T" | "U"
                      | "V" | "W" | "X" | "Y" | "Z" ;
 digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
 white space = ? white space characters ? ;
 all characters = ? all visible characters ? ;
</syntaxhighlight>

For example, a syntactically correct program then could be:
<syntaxhighlight lang="pascal">
 PROGRAM DEMO1
 BEGIN
   A:=3;
   B:=45;
   H:=-100023;
   C:=A;
   D123:=B34A;
   BABOON:=GIRAFFE;
   TEXT:="Hello world!";
 END.
</syntaxhighlight>

The language can easily be extended with [[control flow]]s, arithmetical expressions, and Input/Output instructions. Then a small, usable programming language would be developed.