rir <rirans@comcast.net> writes:
> On Thu, Oct 07, 2021 at 04:24:16PM -0400, Tom Lane wrote:
>> BTW, as it stands, the diagram is ambiguous
>> because there are two ways to parse
>> FETCH cursor_name
>> ... is <direction> present but empty, or omitted altogether?
> I am confident you know what you mean, but I don't. At the _parsing_
> stage how is any distinction between emptiness and omission?
Bison certainly makes a distinction, because it would have two different
production paths it could follow if the actual grammar looked like this
(which it doesn't). It doesn't care whether the emitted parse tree
would be the same. Indeed, it would be possible for the two cases to
create different parse trees.
regards, tom lane