[antlr-interest] Left factor? Syntactic predicates? Or another solution?

[Naveen Chawla]

I am trying to write an English grammar with ANTLR and have simplified a
particular problem to a particular subset for your convenience. (I'm using
ANTLRWorks 1.3)

grammar predicate;


predicate : 'verb' complement?;

      complement: indirectObject? object;

                indirectObject :  nounPhrase;

                object : nounPhrase;

                               nounPhrase : 'the' adjectivePhrase? 'noun';

                                            adjectivePhrase : '<Ving>'
complement?;

gives

"error(211): predicate.g:7:14: [fatal] rule complement has non-LL(*)
decision due to recursive rule invocations reachable from alts 1,2.  Resolve
by left-factoring or using syntactic predicates or using backtrack=true
option."

Is somebody easily able to left-factor this while preserving the grammar? Or
syntactically predicating if better? Sorry if I sound daft! I should say
that taking away the "?" from either adjectivePhrase or indirectObject does
not produce this error, but they are necessary.

Many thanks!
N
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