[LinkGrammar4R] We need higer-level API?

Thank Bradford Folkens for reporting the bug that sometime LinkGrammar4R just crashes when Linkage.new is called. It occurs since there is no linkage from parsing result. Thus, in Linkage.new, the index was checked before calling linkage_create. If the index is out of range, the exception will be raised.

However, I feel like LinkGrammar4R need more higher-level API that free us for checking these index. It may be an iterator?

iterateLinkage(sent, opt).each{|linkage| 
    .....
}

or 

parsedSentence.eachLinkage(opt) {|linkage|
   ......
}