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Stanford CoreNLP provides a set of natural language analysis tools which can take raw English language text input and give the base forms of words, their parts of speech, whether they are names of companies, people, etc., normalize dates, times, and numeric quantities, mark up the structure of sentences in terms of phrases and word dependencies, and indicate which noun phrases refer to the same entities. It provides the foundational building blocks for higher level text understanding applications.

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package edu.stanford.nlp.trees.tregex.tsurgeon;

import java.util.List;
import java.util.Map;
import edu.stanford.nlp.trees.Tree;
import edu.stanford.nlp.trees.Trees;
import edu.stanford.nlp.trees.tregex.TregexMatcher;

/**  Pruning differs from deleting in that if a non-terminal node winds up having no children, it is pruned as well.
 * @author Roger Levy ([email protected])
 */
class PruneNode extends TsurgeonPattern {

  public PruneNode(TsurgeonPattern[] children) {
    super("prune", children );
  }

  public PruneNode(List children) {
    this(children.toArray(new TsurgeonPattern[children.size()]));
  }

  @Override
  public TsurgeonMatcher matcher(Map newNodeNames, CoindexationGenerator coindexer) {
    return new Matcher(newNodeNames, coindexer);
  }

  private class Matcher extends TsurgeonMatcher {
    public Matcher(Map newNodeNames, CoindexationGenerator coindexer) {
      super(PruneNode.this, newNodeNames, coindexer);
    }

    @Override
    public Tree evaluate(Tree tree, TregexMatcher tregex) {
      boolean prunedWholeTree = false;
      for(TsurgeonMatcher child : childMatcher) {
        final Tree nodeToPrune = child.evaluate(tree, tregex);
        if(pruneHelper(tree,nodeToPrune) == null)
          prunedWholeTree = true;
      }
      return prunedWholeTree ? null : tree;
    }
  }

  private static Tree pruneHelper(Tree root, Tree nodeToPrune) {
    if(nodeToPrune==root)
      return null;
    Tree parent = nodeToPrune.parent(root);
    parent.removeChild(Trees.objectEqualityIndexOf(parent,nodeToPrune));
    if(parent.children().length==0)
      return pruneHelper(root,parent);
    return root;
  }
}