Re: How to write the BNF

[Hans Aberg]

On 10 Mar 2008, at 15:55, Sharan Basappa wrote:

> I would like to know how to write BNF for code blocks that have
> optional block enclosing symbols like {}
> For example, the following statements are both valid:
>
> if () $printf();
>
> if()
> {
>   func1;
>   func2;
> }
>
> How to I specify that {} are optional when number of statement is  
> just one.

One way to do it, is to write it as EBNF, and then use rewrite rules  
to BNF. Search for "EBNF" here
  http://lists.gnu.org/pipermail/bug-bison

Or directly
  AorNone:
       /* empty */
    | A
The empty expansion has no token - I just put in a comment for  
clarification. Also see the Bison manual.

> Also, when I write a BNF for a new lanugage, the words that are
> reserved are categorized as keywords.
> What about symbols like {} etc. What are they categorized as?

In Bison, they are called "tokens", "terminals, or "grammar  
constants". This includes also defined variables and such -  
everything that comes directly from the lexer (generated by say  
Flex). Bison parses only tokens.

  Hans Aberg