1 files changed, 73 insertions, 0 deletions
diff --git a/decoder/tree_fragment.h b/decoder/tree_fragment.h
index 83cd1c1e..b1dbbae0 100644
--- a/decoder/tree_fragment.h
+++ b/decoder/tree_fragment.h
@@ -1,6 +1,7 @@
 #ifndef TREE_FRAGMENT
 #define TREE_FRAGMENT
 
+#include <queue>
 #include <iostream>
 #include <vector>
 #include <string>
@@ -9,6 +10,8 @@
 
 namespace cdec {
 
+class BreadthFirstIterator;
+
 static const unsigned NT_BIT       = 0x40000000u;
 static const unsigned FRONTIER_BIT = 0x80000000u;
 static const unsigned ALL_MASK     = 0x0FFFFFFFu;
@@ -36,6 +39,15 @@ class TreeFragment {
   // (S (NP a (X b) c d) (VP (V foo) (NP (NN bar))))
   explicit TreeFragment(const std::string& tree, bool allow_frontier_sites = false);
   void DebugRec(unsigned cur, std::ostream* out) const;
+  typedef BreadthFirstIterator iterator;
+  typedef ptrdiff_t difference_type;
+  typedef unsigned value_type;
+  typedef const unsigned * pointer;
+  typedef const unsigned & reference;
+
+  iterator begin() const;
+  iterator end() const;
+
  private:
   // cp is the character index in the tree
   // np keeps track of the nodes (nonterminals) that have been built
@@ -49,6 +61,67 @@ class TreeFragment {
   std::vector<TreeFragmentProduction> nodes;
 };
 
+struct TFIState {
+  TFIState() : node(), rhspos() {}
+  TFIState(unsigned n, unsigned p) : node(n), rhspos(p) {}
+  bool operator==(const TFIState& o) const { return node == o.node && rhspos == o.rhspos; }
+  bool operator!=(const TFIState& o) const { return node != o.node && rhspos != o.rhspos; }
+  unsigned short node;
+  unsigned short rhspos;
+};
+
+class BreadthFirstIterator : public std::iterator<std::forward_iterator_tag, unsigned> {
+  const TreeFragment* tf_;
+  std::queue<TFIState> q_;
+  unsigned sym;
+ public:
+  explicit BreadthFirstIterator(const TreeFragment* tf) : tf_(tf) {
+    q_.push(TFIState(tf->nodes.size() - 1, 0));
+    Stage();
+  }
+  BreadthFirstIterator(const TreeFragment* tf, int) : tf_(tf) {}
+  const unsigned& operator*() const { return sym; }
+  const unsigned* operator->() const { return &sym; }
+  bool operator==(const BreadthFirstIterator& other) const {
+    return (tf_ == other.tf_) && (q_ == other.q_);
+  }
+  bool operator!=(const BreadthFirstIterator& other) const {
+    return (tf_ != other.tf_) || (q_ != other.q_);
+  }
+  void Stage() {
+    if (q_.empty()) return;
+    const TFIState& s = q_.front();
+    if (s.rhspos < 0) {
+      sym = tf_->nodes[s.node].lhs;
+    } else {
+      sym = tf_->nodes[s.node].rhs[s.rhspos];
+      if (IsInternalNT(sym)) {
+        q_.push(TFIState(sym & ALL_MASK, 0));
+        sym = tf_->nodes[sym & ALL_MASK].lhs;
+      }
+    }
+  }
+  const BreadthFirstIterator& operator++() {
+    TFIState& s = q_.front();
+    const unsigned len = tf_->nodes[s.node].rhs.size();
+    s.rhspos++;
+    if (s.rhspos > len) {
+      q_.pop();
+      Stage();
+    } else if (s.rhspos == len) {
+      sym = 0;
+    } else {
+      Stage();
+    }
+    return *this;
+  }
+  BreadthFirstIterator operator++(int) {
+    BreadthFirstIterator res = *this;
+    ++(*this);
+    return res;
+  }
+};
+
 inline std::ostream& operator<<(std::ostream& os, const TreeFragment& x) {
   x.DebugRec(x.nodes.size() - 1, &os);
   return os;