User Token Numbers

[Akim Demaille]

While writing test cases I fell on some weird behaviors: 1.28 (I don't
know for 1.3x, I don't have it at hand, but I'd say it behaves
equally) accepts that you

%token FOO 2

although 2 is used for $undefined.  Nice from it to accept, but it
would be better if the parser knew that.  It does not, and FOO and
$undefined do collide at runtime.

1.5x refuses:

foo.y:32: tokens "1" and $undefined. both assigned number 2

(the message showed up as part of the various clean ups, so they _are_
useful :).


Neither is OK I guess.  But I would like to know more from POSIX, in
particular, I would like to make sure that EOF (= 0) is the only
number that is reserved.


Also, but that's another matter: what does POSIX say about
reduce/reduce conflicts?