Re: What does error message "fatal error: start symbol grammar does not derive any sentence" mean?

[Tomas Crhak]

Hi joe,

add another rule to exp, eg

exp: NUMBER { $$ = convert_str_to_int($1); }
   | /* you rules */

otherwise exp cannot be derived as all the other rules involve
exp itself.

-tomas

On Tue, 2009-08-04 at 22:12 +0100, address@hidden wrote:
> Thanks for your help.
> I have attached the latest listing of the program in question.  When I run
> Bison now, then the messages I get from that are...
> parse.y: warning: 8 useless nonterminals and 30 useless rules
> parse.y:52.1-7: fatal error: start symbol grammar does not derive any
> sentence
> 
> I believe that The particular code it refers to is...
> %%
> grammar:  domains
>         constants
>         predicates
>       ;
> 
> My intention is that it reads a set of domains...
> typically each one is to a line of a format...
> D0 11 0 10  // domainName, number_of_values, floor_value, ceil_value
> ...
> Then reads a set of constants...
> typically each one to a line of a format...
> X0 D0 9
> 
> Then reads and processes a set of predicates, each one to a line, which
> may appear as...
> or(lt(mul(X0,X1),X2),ge(abs(sub(X3,X4)),X5))
> 
> However,  I have no precedent or pro-forma for such as 'grammar' above.  I
> think that the domains constants predicates sequence I've written will
> read all the
> domains, then all the constants then all the predicates without allowing
> any regression through any of them (eg a domain in the constants).
> 
> That the start symbol 'grammar' cannot derive any sentence only suggests
> to me that the grammar high level nonTerminal cannot access it's
> subsidiary terminals and non-terminals, but the exact cause is not yet
> clear to me.
> 
> The classic example such as p75  of lex & yacc...[1995 Levine et al]
> statement_list: statement '\n'
>        statement_list  statement '\n'
>     ;
> ...doesn't shed much light on my codes attached below, where I must read a
> group of domains, followed by a group of constants, followed by a group of
> predicates.
> 
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