Re: Empty token sequence

Cesare Zecca wrote:
> ID and GROUP_ID share a common prefix and cause a lookahead problem.

Actually, the problem is that there are two ways to parse an <ID>,
either
   Factor() -> Id() -> <ID>
or
   Factor() -> GroupId() -> <ID>
The parser doesn't know which one to choose.

For the example grammar, this is unnecessary, so the fix is to
eliminate the redundancy.

Approach 1: Eliminate Id() and GroupId() and replace the body of
Factor() with the body of GroupId().  This results in the simplest
grammar.  Then <ID> would be parsed via
   Factor() -> <ID>

Approach 2: Remove <ID> from GroupId(), since it is already covered by
the Id() call in Factor().  Then <ID> would be parsed via
   Factor() -> Id() -> <ID>

Hope this helps!