Re: Useless nonterminals - what and why?

[Hans Aberg]

At 10:40 +0100 0-11-21, Akim Demaille wrote:
>BTW, I just discovered a feature I was unaware of, which is related to
>the diagnostic you gave on this grammar:
..
>%token element
>%nterm list
>%%
>list : list element {}
>/tmp % LC_ALL=C bis list.y
>list.y contains 1 useless nonterminal and 1 useless rule
>list.y:5: fatal error: Start symbol list does not derive any sentence
>
>
>/tmp % cat list.y
>%token element
>%nterm list
>%%
>list : list element {} | element {}

I gather it is the %nterm declaration, which appears to be undocumented.

Do you know exactly what it means (that is, what is required for Bison to
not complain on such a %nterm declared variable)?

  Hans Aberg