[antlr-interest] Specifying optional elements in a tree grammar.

[Gavin Lambert]

At 06:12 26/03/2009, Jim Idle wrote:
>>  )? ->^(SELECTCLAUSE selectClause ^(INTOCLAUSE intoClause)? 
>> ^(FROMCLAUSE fromClause)? ^(WHERECLAUSE whereClause)?);
[...]
>>querySpecification :
>>  ^(SELECTCLAUSE selectClause ^(INTOCLAUSE intoClause)? 
>> ^(FROMCLAUSE fromClause)? ^(WHERECLAUSE whereClause)?)
>>  ;
[...]
>  ^(SELECTCLAUSE selectClause (^(INTOCLAUSE intoClause))? 
> (^(FROMCLAUSE fromClause))? (^(WHERECLAUSE whereClause))?)
>
>Because the ^( xxxxx) is a tree specification and needs to be 
>enclosed to make it optional.

Interesting that it seems to work in the rewrite specification, 
though.  Shouldn't they be consistent?  (It's debatable which way 
is "better", but it's just confusing if they're different.)