At 01:24 2/10/2009, Naveen Chawla wrote:
>Thanks so much! Yes, I tried complement: object object?
>coincidentally just before I read your message and it worked.
>Good news is that in the real grammar they ARE actually
>equivalent. But is there no way of making 'indirectObject' and
>'object' appear as they are in the end structure if there are 2
>'object's in a row (they have slightly different meanings even
>though syntactically the same)? Would a syntactic predicate solve
>this? For example, complement: (indirectObject
>object)=>indirectObject object | object; Is this the right one?
>(it doesn't seem to work on ANTLRWorks) Many many thanks, N
Which rules it passes through shouldn't have any bearing on the
semantic meaning; the rules should just be concerned with matching
logical units of tokens.
You can assign different meanings to the objects via altering the
output AST, eg:
complement
: (o1=object -> ^(DIRECT $o1))
(o2=object -> ^(INDIRECT_DIRECT $o1 $o2))?
;
(There are lots of other possible tree layouts, of course.)
If you're carrying out some action directly rather than outputting
an AST, you can still use a similar technique (putting some of the
code inside the optional block) to get different behaviour if the
second object is actually present.
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