1 files changed, 24 insertions, 0 deletions
diff --git a/extractor/phrase_builder.cc b/extractor/phrase_builder.cc
index 7f3447e5..c4e0c2ed 100644
--- a/extractor/phrase_builder.cc
+++ b/extractor/phrase_builder.cc
@@ -19,3 +19,27 @@ Phrase PhraseBuilder::Build(const vector<int>& symbols) {
   }
   return phrase;
 }
+
+Phrase PhraseBuilder::Extend(const Phrase& phrase, bool start_x, bool end_x) {
+  vector<int> symbols = phrase.Get();
+  int num_nonterminals = 0;
+  if (start_x) {
+    num_nonterminals = 1;
+    symbols.insert(symbols.begin(),
+        vocabulary->GetNonterminalIndex(num_nonterminals));
+  }
+
+  for (size_t i = start_x; i < symbols.size(); ++i) {
+    if (vocabulary->IsTerminal(symbols[i])) {
+      ++num_nonterminals;
+      symbols[i] = vocabulary->GetNonterminalIndex(num_nonterminals);
+    }
+  }
+
+  if (end_x) {
+    ++num_nonterminals;
+    symbols.push_back(vocabulary->GetNonterminalIndex(num_nonterminals));
+  }
+
+  return Build(symbols);
+}