empty production alternative: Maybe you are missing the "empty" keyword in Letter

[arater]

`
/* Misc ------------------------------------------------------------------*/

Integer ::= Digit | Integer Digit ;
Digit ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" | empty ;

Letters ::= Letter Letters | empty;
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' | empty ;

Char ::= PrintableChar | WhitespaceChar ;
PrintableChar ::= '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' | "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" | OtherSymbols ;

WhitespaceChar ::= Space | Tab | NewLine ;
OtherSymbols ::= '!' | '@' | '#' | '$' | '%' | '^' | '&' | '*' | '(' | ')' | '-' | '+' | '=' | '{' | '}' | '[' | ']' | '|' | '\' | ':' | ';' | '"' | ''' | '<' | '>' | ',' | '.' | '/' | '?' ;
Space ::= ' ' ;
Tab ::= #x9 ;
NewLine ::= CarriageReturn | LineFeed ;

CarriageReturn ::= '\r' ;
LineFeed ::= '\n' ;
`

I am trying to create bnf file for regular expressions grammars but i am getting always this error and i do not understand why it is happening? Can you help me or do you have any regular expressions bnf file that work witc gocc, can you provide me?

[awalterschulze]

You can try single quotes for Digit as in '0' - '9'
And gocc syntax is different it isn't :==, but only :

You could also try 'A' - 'Z' so you don't have to list all alternatives

But I am just providing some random suggestions, think it will help to go in the right direction, but not necessarily fix all issues