What is the EBNF grouping in yacc

Question

I am writing a program grammar with lex/yacc. I have an issue about ambiguity of grammar and i need to look EBNF grammar. When I searched semantic of yacc and its declarations, i see grouping({.....}) but i do not know how i can initialize it. For example options([.....]) initialize with |.

%token PROGRAM ID SEMICOLON
    program: 
             PROGRAM ID SEMICOLON
             | PROGRAM ‘,’ ID SEMICOLON

is there any way for grouping like that?

Answer 1

yacc does not support EBNF, so you need to convert the EBNF operators to simple BNF to use in yacc. In general, each such operator will require introducing a new symbol. So

[...] becomes <new-symbol> with

<new-symbol> ::= ε | ...

{...} becomes <new-symbol> with¹

<new-symbol> ::= ε | <new-symbol> ...

(...) becomes <new-symbo> with

<new-symbol> ::= ...

---

¹_{If there are any | operators in ..., you need to insert <new-symbol> after each one in this substitution}