yacc priorities and reduce-reduce conflicts

Say you have in some lang.y file:
%token PRIORITY_BOTTOM TILDE
(...)
%nonassoc PRIORITY_BOTTOM
%nonassoc TILDE
(...)
a : b %prec PRIORITY_BOTTOM
| TILDE b
;


and say that these 2 rules create a red-red conflict in some state:
a : b_ (n)
a : TILDE b_ (n+1)


I thought that the priority declarations could solve the conflict in
favour of the rule (n+1) because its priority is the priority of
TILDE, wheras the priority of the rule (n) is the one of
PRIORITY_BOTTOM.


But this is wrong. yacc considers that these priorities do not solve
the conflict. This seems to mean that when a rule is reduced, its
priority is not infered from its terminals ---which is surprising.


I did not find any documentation concerning this issue. Neither with
`man yacc`, nor in (my version of) O'Reilly lex&yacc book.


Could anyone help?


Thanks in advance,
--Frederic
[Precedences only solve shift/reduce conflicts. You need to flatten
your grammar, see chapter 8 of our book. -John]




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